Janus biomaterials in regenerative medicine: structural asymmetry as a platform for multifunctional tissue repair

1 Introduction

Regenerative medicine aims to restore the structure and function of damaged tissues by coordinating interconnected biological processes, including inflammation, angiogenesis, cell recruitment, extracellular matrix deposition, and tissue remodeling (Sharifi et al., 2025). Achieving this objective requires biomaterials that not only provide structural support but also dynamically regulate cellular behavior, biochemical signaling, and the evolving tissue microenvironment throughout the healing process (Zhou L. et al., 2023). However, conventional biomaterials are generally designed as homogeneous constructs with uniform physicochemical properties, limiting their capacity to simultaneously perform multiple, and often opposing, biological functions, such as promoting tissue regeneration while preventing bacterial colonization or postoperative tissue adhesion (Yang Y. et al., 2025).

This is where the principles of soft matter have proven to be a successful approach to overcoming such limitations by providing the ability of controlling interfaces, phase organization, surface energy, wettability and compartmentalized architectures with precision. In this context, Janus materials have garnered growing interest as anisotropic systems, defined as materials where different chemical, physical or mechanical properties are spatially localized within a single construct (Mulaparthy et al., 2025). Such an asymmetry also facilitates the coexistence of complementary functions while leaving the individual role of each compartment intact, and promotes cooperation between the interfaces, which is especially attractive for the application of regenerative medicine, where different biological responses are required over the same interface (Le et al., 2019).

The Janus concept was first introduced in the field of soft matter in amphiphilic Janus beads that were shown to be able to stabilize an oil–water interface more efficiently than a conventional surfactant (Casagrande et al., 1989). Over the past few decades, Janus architectures have increasingly been scaled up from simple particles to multifunctional platforms, such as nanoparticles, fibers, membranes, thin films, hydrogels, and 3D constructs (Dey et al., 2025; Ganguly et al., 2026). As illustrated in Supplementary Figure S1A, this evolution has extended the application of Janus materials from interfacial engineering to tissue engineering, smart wound dressings, injectable biomaterials, advanced three-dimensional (3D) and four-dimensional (4D) bioprinting, immunomodulatory systems, and artificial intelligence (AI)-assisted biomaterial design.

Although several reviews have described specific Janus materials or individual biomedical applications (Mao H. J. et al., 2026; Mozhdehbakhsh Mofrad et al., 2025; Yang Y. et al., 2025), a comprehensive analysis integrating fabrication strategies, structural asymmetry, multifunctional behavior, and regenerative mechanisms within a unified soft matter framework remains lacking. Specifically, recent developments that include gradient architectures, bioactive glass integration, metabolic regulation, stimuli-responsive systems and 4D bioprinting are not well summarized. Considering these aspects is crucial for setting up structure–property–function relationships and to rational design the next-generation of Janus biomaterials.

Driven by these developments, diverse fabrication technologies, including electrospinning, microfluidics, electrospray, layer-by-layer assembly, and advanced 3D and 4D bioprinting; have enabled increasingly sophisticated Janus architectures with precisely controlled compartmentalization and functionality (Yan et al., 2025). This technological progress is reflected in the continuous growth of scientific publications over the past 2 decades (Supplementary Figure S1B), with a pronounced acceleration after 2015. The expansion parallels greatly the progress of key technologies such as Additive Manufacturing, microfluidic fabrication, precision medicine, stimuli-responsive materials, advanced electrospinning, as well as the more recent AI-assisted biomaterial design, which have significantly expanded the design space of Janus systems.

These technological advances have enabled Janus biomaterials to address diverse regenerative challenges. Guided bone and periodontal regeneration using Janus membranes with asymmetric architectures has been widely studied for its osteogenic, antibacterial and immunomodulatory properties (Li Y. et al., 2025). Likewise, Janus hydrogels have advanced the use of compartmentalized biomaterials in the field of wound healing, hemostasis, tissue sealing, and chronic wound management (Yang Y. et al., 2025). Concurrently, the adoption of bioactive delivery systems, metabolic control and stimuli-responsive capabilities have expanded the potential of Janus platforms in precision regenerative medicine (Priyadharshini and Sabarees, 2026).

Despite these advances, the field remains fragmented across material types, processing methods, and biochemical applications. The relationship between structural design, manufacturing strategies, multifunctional performance, and regenerative outcomes is often treated independently; meanwhile, critical issues such as scalability, long-term design stability, morphological compatibility, and clinical application have not been adequately integrated (Mao H. J. et al., 2026). To address this gap and ensure a representative and reproducible synthesis of the current literature, a structured search strategy was adopted. A literature search was conducted across the PubMed, Web of Science, and Scopus databases, with the search primarily focused on publications from January 2015 to 2026, corresponding to the period of accelerated development and growing interest in Janus biomaterials research. The search combined the following keywords using Boolean operators: (“Janus biomaterial” OR “asymmetric membrane” OR “asymmetric nanoparticle” OR “asymmetric hydrogel”) AND (“tissue regeneration” OR “drug delivery” OR “wound healing” OR “bone regeneration” OR “tendon repair” OR “cartilage regeneration” OR “remote guidance”). Only peer-reviewed original research articles and reviews published in English were considered. Studies unrelated to biomedical or regenerative applications, conference abstracts, and duplicate records were excluded. Reference lists of the selected articles were additionally screened to identify further relevant studies not captured by the initial search.

In this review, we provide a comprehensive and critical overview of functional Janus biomaterials from a soft matter perspective. We first discuss the fundamental principles governing Janus architectures and the principal fabrication technologies. We then examine how structural asymmetry enables advanced functions, including controlled and sequential drug delivery, barrier and bioactive performance, antimicrobial and anti-adhesive activity, exudate management, immunomodulation, remote responsiveness, and metabolic regulation of tissue regeneration. Finally, we summarize current biomedical applications and discuss future opportunities and remaining translational challenges, providing a unified framework for the rational design of next-generation Janus biomaterials for regenerative medicine.

2 Engineering strategies and structural platforms

2.1 Electrospinning-derived Janus nanofibers

Electrospinning is a widely used technique for fabricating fibrous scaffolds that closely mimic the architecture of the native extracellular matrix, making it particularly suitable for tissue engineering applications (Keshvardoostchokami et al., 2020; Zulkifli et al., 2023). A high-voltage field draws the polymer solution into a Taylor cone, from which a charged jet is stretched into continuous micro- or nanoscale fibers (Chen et al., 2023). Beyond monolithic fibers, electrospinning can also generate Janus nanofibers, which combine two chemically or functionally distinct compartments within a single fiber, integrating contrasting properties such as hydrophilicity/hydrophobicity or fast/sustained release into one construct (Abadi et al., 2022). Several configurations achieve Janus or Janus-like morphologies, including side-by-side, uniaxial, coaxial, and multilayer approaches, which differ in fabrication complexity and degree of compartmentalization (Wang P. et al., 2023; Zhang J. Y. et al., 2025).

Side-by-side electrospinning is the primary one-step route to Janus fibers, using dual parallel spinnerets to place two chemically distinct phases adjacently along a partially overlapping interface. The main issue is that the electrostatic force between the identically charged jets tends to separate the fluids prior to fiber formation. These were overcome by using eccentric spinners with round and crescent-shaped Teflon coated outlets which redistribute surface charge and stabilize the Janus Taylor cone (Yu et al., 2016). On this platform, a polyvinylpyrrolidone (PVP)/ethyl cellulose (EC) wound dressing was produced, with ciprofloxacin in the hydrophilic PVP side for rapid bactericidal release and silver nanoparticles (AgNPs) in the hydrophobic EC side for sustained activity against Gram-positive and Gram-negative bacteria (Yang et al., 2020). A related pH-responsive Janus system later co-delivered octenidine and curcumin from separate compartments, releasing them sequentially at the acidic pH of infected wounds for synergistic, pH-dependent antibacterial action against E. coli and Staphylococcus aureus (Amarjargal et al., 2024).

The side-by-side approach can be further extended to the fabrication of three-compartment fibers. A tri-fluid eccentric spinneret segregated beeswax, quercetin, and ketoprofen into separate sections, combining a hydrophobic barrier with antioxidant and anti-inflammatory release to limit adhesion during tendon healing in vivo (Xu L. et al., 2024). The approach has also been extended to regenerative strategies, in which polyvinylpyrrolidone (PVP)/polycaprolactone (PCL) Janus microfragments co-loading magnesium oxide (MgO) and poly-γ-glutamic acid (PGA) gave a synchronized 30-day release of Mg²⁺, O₂, and PGA that suppressed reactive oxygen species (ROS) and inflammatory signalling and drove mesenchymal stem cell chondrogenesis (Chaudhary et al., 2025).

A simpler route to Janus morphology uses monoaxial electrospinning of phase-incompatible polymer blends. As the jet is stretched and the solvent evaporates within milliseconds, the polymers demix into distinct domains and the asymmetric morphology is kinetically arrested before the components can remix. The resulting geometry depends on the polymer pair, blend ratio, and solvent volatility, ranging from cleanly bisected Janus structures to core–sheath or matrix-and-domain architectures. Using a purpose-designed uniaxial spinneret that provided sufficient interfacial contact and residence time to form an interface stable against jet instability, PVP/PCL Janus fibers co-loaded with Rana chensinensis skin peptides (RCSPs) and AgNPs were produced (Figure 1A), showing skin-mimetic mechanics, first-order RCSP release, antibacterial activity, and wound healing in a full-thickness model in vivo (Ji et al., 2021).

The same phase-separation principle has supported biphasic release of Zn²⁺ and an immunomodulatory agent from ZIF-8/FK506 compartments for periodontal regeneration (Sun et al., 2022), while a still simpler implementation relied only on stratification of a PCL/PVP solution within the syringe to confine AgNPs to one compartment, giving activity against Gram-positive and Gram-negative strains (Li et al., 2019). Such single-needle implementations lower the equipment demands of Janus fiber production, making the approach more accessible than multi-fluid spinneret designs.

Coaxial electrospinning primarily produces core–shell fibers, in which a shell encapsulates a core for the protected delivery of sensitive bioactive molecules such as growth factors and peptides. Several studies have shown that it can be reconfigured toward true Janus or Janus-hybrid architectures by combining concentric geometry with parallel fluid arrangements. A three-fluid modification used an outer solvent shell to stabilize two parallel core streams and yield uniform Janus fibers (Yu et al., 2017). In a related co-shell strategy, an unspinnable outer solvent integrated the parallel hydroxypropyl methylcellulose (HPMC)/PVP streams and kept icariin amorphous, improving its dissolution and permeation 11.2- and 16.2-fold, with potential for trans-blood–brain barrier delivery (Figure 1B) (Sun et al., 2024). Extending this toward permanent hybrid structures, a pH-sensitive hydroxypropyl methylcellulose acetate succinate (HPMCAS) shell enclosed two side-by-side cores of 5-fluorouracil-loaded ethyl cellulose and bioadhesive polyethylene oxide, achieving colon-targeted, prolonged drug absorption in vivo beyond that of conventional core–shell or Janus fibers (Zhou J. et al., 2023).

In a further adaptation directed at wound healing, the Janus configuration was generated within the sheath through phase separation of a PCL/PVP blend while corn peptides were carried in the core. The hydrophilic PVP enabled rapid peptide release (∼92% in 80 min) whereas the hydrophobic PCL preserved network integrity, and the resulting groove-like surface promoted fibroblast proliferation and accelerated wound healing through ROS scavenging in vivo (Ji et al., 2020). Coaxial electrospinning therefore remains fundamentally a core–shell method, but its geometric and fluidic variants provide an additional route to compartmentalized Janus and Janus-hybrid architectures.

Whereas the preceding strategies confine the Janus interface within a single fiber, an alternative route relocates the asymmetry to the architectural scale. By sequentially electrospinning distinct fibrous strata onto a common collector, a biphasic or multilayer membrane is produced in which each internally homogeneous stratum contributes a discrete function, so that the Janus character emerges from the assembled stack rather than any single fiber. This addresses a shortcoming of conventional barrier membranes, whose monolithic structure presents the same surface to two biologically opposed compartments, whereas an asymmetric bilayer can satisfy the divergent demands of a soft-tissue- and a hard-tissue- or wound-facing side (Zhang J. Y. et al., 2025). A representative example targets guided tissue regeneration under diabetic conditions. A dual-functional Janus bilayer membrane paired a dense thiolated polyethylene glycol (TPG)/poly (lactic-co-glycolic acid) (PLGA)/polycaprolactone (PCL) barrier side with a nano-hydroxyapatite-modified polyethylene glycol (PEG) hydrogel side. In a diabetic periodontitis model, it reduced oxidative stress, modulated the local inflammatory response under simulated diabetic and inflammatory conditions, and enhanced osteogenic and cementogenic differentiation (Wang F. et al., 2026). The same asymmetric-bilayer logic has been applied to irregular wound healing through in situ deposition. A handheld electrospinning device (Figure 1C) sequentially deposited a hydrophilic poly (L-lactic acid) (PLLA)/gelatin/magnesium oxide (MgO) layer and a hydrophobic PCL outer layer directly onto the wound, so that the outer layer served as a bacterial barrier while MgO in the inner layer modulated inflammation and promoted vascularization and epithelialization in vivo (Zhou T. et al., 2024).

More recent biphasic membranes have shifted from passive bilayers toward stimuli-responsive, environmentally adaptive systems. Several such dressings combine unidirectional exudate transport with added functions, including anthocyanin-based pH-responsive infection sensing and antioxidant activity (Guo K. et al., 2025). Extending single functions toward staged therapy, a bilayer pairing a polyvinylidene fluoride (PVDF) outer barrier with a multi-drug inner layer released its cargo in a programmed sequence for the staged treatment of chronic infected wounds (Qu et al., 2025). The same asymmetric design has been applied to an in situ electrospun dressing that combines ultraviolet (UV) protection with directional fluid management (Lin et al., 2025) and, beyond planar wounds, to a tubular nerve conduit whose heparin-functionalized chitosan inner layer delivered nerve growth factor (NGF) while a piezoelectric PVDF/ZnO outer layer activated the NGF/tropomyosin receptor kinase A (TrkA) pathway, achieving nerve recovery comparable to autograft in a rat sciatic-nerve model (Yi et al., 2025).

The same sequential-deposition logic extends to trilayer architectures, in which an intermediate stratum adds a structural or functional dimension while the asymmetry between the outer faces is preserved. Grading fibre diameter across three strata established a continuous hydrophilic-to-hydrophobic wettability gradient, mimicking the dermis–epidermis transition, that directed exudate away from the wound bed (Gong et al., 2025), while an interposed, hot-pressed polyurethane (PU) layer in a PVDF/PU/cotton dressing stabilized the gradient and enforced rapid unidirectional transport with high resistance to reverse flow (Liu et al., 2023). In a hemostatic variant, an asymmetrically wetted trilayer stacked a hydrophobic, low-adherent polylactic acid (PLA) inner layer facing the wound, a PLA/silk fibroin (P2S8) drainage interlayer, and a superabsorbent outer layer carrying cerium-doped bioactive-glass granules (Ce-BG@PDE) (Figure 1D). The graded increase in hydrophilicity and decrease in pore size from the inner to the outer face set up a self-pumping capillary gradient that drew excess serum away from the wound while resisting backflow, and the bioactive glass outer layer additionally provided hemostatic and antibacterial activity (Wang B. et al., 2026).

The choice of the electrospinning strategy will be determined by the requirement for a desired level of asymmetry, functional compartmentalization, and control of bioactive delivery. Side by side electrospinning is the simplest and most direct method for creating true Janus fibers that allows for distinct compartments with independently tunable loading, wettability, and interfacial properties, ideal for biphasic delivery and spatially differentiated functions (Abadi et al., 2022). The dual jets are susceptible to electrostatic repulsion, which means their geometry, compatibility of solution components, conductivity, viscosity, voltage, and flow rates must be carefully controlled to achieve stable fabrication (Sun et al., 2024). While core–shell fibers can be produced by coaxial electrospinning, this technique is prone to flow-rate and interfacial instabilities and does not naturally result in lateral Janus organization, making it unsuitable for many applications, especially for bioactive encapsulation, protection, and sustained or controlled release (Parhi and Pachuau, 2025). Monoaxial electrospinning offers the simplest and most accessible route but generally requires phase separation or post-assembly to generate Janus-like architectures, limiting structural control (Ji et al., 2021). In contrast, multilayer, triaxial, and multi-axial approaches enable more complex architectures with multiple functional compartments, programmable sequential release, and tunable mechanical and biological functions, but at the expense of greater fabrication complexity, characterization demands, and scalability challenges (Annie Bligh et al., 2023). Overall, side-by-side systems are preferable for exposed, independently functionalized Janus surfaces; coaxial systems for encapsulation and sustained release; monoaxial approaches for simplicity; and multilayer/triaxial systems for advanced multifunctional and sequential therapies (Annie Bligh et al., 2023; Parhi and Pachuau, 2025).

Collectively, electrospinning enables versatile Janus architectures for spatially controlled multifunctional regeneration.

2.2 Microfluidics and electrospray-engineered Janus nanoparticles

2.2.1 Droplet-based microfluidic fabrication

Microfluidic technology provides a highly precise platform for the fabrication of functional Janus biomaterials by manipulating extremely small volumes of liquid, typically at the nanoliter or picoliter scale, within micro-scale channels (Zhao et al., 2020). This method is performed in laminar flow conditions (Reynolds number low, typically less than 1), which will ensure that there is no spontaneous mixing in the system and maintain distinct compositional boundaries between the particle’s compartments (Chen et al., 2025; Yu et al., 2016) (Figure 2). This fabrication technique is based on the combined effect of shear force, surface tension and capillary force, which is quantitatively assessed by the dimensionless Capillary number (Ca) (Chen et al., 2025). Typically, two immiscible precursor solutions are fed into microfluidic channels where they merge under carefully controlled flow conditions to generate biphasic droplets with very reproducible droplet size and morphology. Droplet generation can be performed by T-junction, Y-junction, cross-junction, co-flow, step-T junction or flow-focusing geometries, each with a different hydrodynamics capability of controlling the droplet size, monodispersity and compartmentalization (Chen et al., 2025; Ma Z. et al., 2024; Yu et al., 2016). Within these configurations, flow-focusing devices are especially appealing due to their ability to provide high uniformity of droplets and their common use in Janus micro- and nanoparticles fabrication (Ma L. et al., 2024).

There are mainly two methods to generate droplets: passive and active microfluidic methods (Zhu and Wang, 2016). Passive microfluidics is the most popular method as it produces droplets without any additional energy input, and only involves flow rates and the geometry of the channels, which is simple, robust, and reproducible (Ma L. et al., 2024; Zhu and Wang, 2016). In contrast, active microfluidic systems employ external stimuli, including electric, magnetic, acoustic, optical, or centrifugal forces, to precisely manipulate droplet formation and positioning. While active systems provide more flexibility and dynamic control, their complexity makes their use at large-scale production is currently limited. In a passive microfluidic system, the splitting of droplets occurs in a variety of characteristic flow regimes such as squeezing, dripping, jetting and rarely, tip-streaming (Ma L. et al., 2024; Zhu and Wang, 2016). The relative flow rates of the dispersed and continuous phases are the most important and controlling factors in these regimes, along with the balance between interfacial tension and viscous shear forces. When squeezing is applied, the interfacial forces take over, yielding droplets that are bigger than the channel dimensions (Ma L. et al., 2024). At higher continuous-phase flow rates, the viscous shear is more dominant, and a dripping regime with very monodisperse droplets is obtained, which are ideal for biomedical applications. Jetting is another phenomenon that occurs at higher flow rates resulting in droplet breakup downstream via hydrodynamic instabilities, while tip-streaming allows the creation of ultrafine droplets at high continuous-to-dispersed phase ratio (Fu et al., 2012). Therefore, it is crucial to control flow conditions in order to achieve desired particle diameter, shape of the compartments as well as uniformity of the particles in the structure to achieve the most effective results (Ma L. et al., 2024).

Several template strategies have been developed to fabricate Janus particles using droplet microfluidics (Supplementary Table S1). In single-emulsion systems, Janus architectures can be generated either through phase separation of two incompatible components dissolved in a common solvent or by directly merging two independent precursor streams into biphasic droplets (Chen et al., 2025). Alternatively, double-emulsion templates, such as oil-in-water-in-oil systems, can be used for hierarchical compartmentalization, which can simultaneously encapsulate hydrophilic and hydrophobic therapeutic agents within different compartments, significantly broadening the scope of Janus carriers in regenerative medicine (Chen et al., 2025; Yang et al., 2012). More sophisticated device designs, including vertically aligned polydimethylsiloxane (PDMS) microchannels, have further enabled the fabrication of non-conventional Janus morphologies such as discoid particles, illustrating the remarkable structural flexibility afforded by microfluidic engineering (Zhang et al., 2021). After droplet generation, the rapid stabilization of the biphasic architecture is necessary to maintain the compartmentalization before interfacial diffusion can take place. Depending on the material system, structural fixation is typically achieved through ultraviolet photopolymerization, thermal curing, ionic crosslinking, or solvent evaporation, thereby transforming transient droplets into permanently anisotropic Janus nanoparticles (Chen et al., 2025). For instance, droplet-based microfluidic devices have been demonstrated for the efficient synthesis of magnetically anisotropic TiO₂/Fe₃O₄ Janus particles within a single microreactor. These particles possess dual properties. The TiO₂ content makes them suitable for medical implants, healthcare products, and bioimaging, while the Fe₃O₄ content provides magnetic properties for precise manipulation via an external field (Saqib et al., 2024). Droplet-based microfluidics offers a superior engineering approach to creating structural platforms with microstructures that are more complicated and closer to native biological tissues, as it allows for ultrafine control of particle size, shape and the distribution of functional cues throughout the structure (Yang et al., 2012).

Tunable flow and emulsion templating allows for precise control of Janus biomaterial size, morphology, compartmentalization, and functionality via microfluidic engineering. This spatial control can recapitulate tissue heterogeneity for regenerative applications, but scalability and throughput will be important challenges.

2.2.2 Electrospray-assisted phase separation

Electrospray, also known as electrohydrodynamic atomization (EHDA), utilizes a high electric potential, typically between 5 and 30 kV, to overcome the surface tension of a polymer solution and deform the liquid meniscus into a conical structure called a Taylor cone (Roh et al., 2005). From the apex of this cone, a thin jet is ejected that rapidly destabilizes to form monodisperse micro- or nanoparticles as the solvent evaporates (Bhaskar et al., 2010). Unlike conventional electrospray or electrospinning, which generally produce isotropic fibers or particles from a single needle, the Janus-forming variant of EHDA employs side-by-side, co-axial, or theta-shaped capillaries to introduce multiple incompatible solutions simultaneously (Roh et al., 2005; Yang et al., 2023) (Figure 3). This technique is particularly suitable for the fabrication of Janus nanoparticles because the solutions co-jet under laminar flow at a low Reynolds number, ensuring that the time required for diffusional intermixing between the phases greatly exceeds the time required for particle solidification (Yang et al., 2023). The mechanism of Janus particle formation involves a complex interplay of physical phenomena following the initial atomization of the compound Taylor cone (Jeevanandam et al., 2023). As droplets are ejected, rapid solvent evaporation increases the local concentration of the polymer components, triggering phase separation through mechanisms such as thermodynamic liquid-liquid phase separation (LLPS), driven by the free energy of mixing, or diffusion-induced phase separation (DIPS), caused by concentration gradients (Bhaskar et al., 2010). The final morphology-ranging from core-shell to acorn, snowman, or dumbbell shapes-is determined by interfacial tension-mediated phase partitioning and the competition between the timescales of phase separation and particle solidification. Key factors governing these Janus architectures include polymer concentration and viscosity, which influence jet stability; solution conductivity, which can drive selective migration of charge carriers to reinforce the interface; and processing parameters such as flow rate, applied voltage, and collection distance (Saqib et al., 2024).

Early foundational studies utilized electrohydrodynamic (EHD) co-jetting of synthetic polymers like poly (acrylamide-co-acrylic acid) (P (AAm-co-AA)) and poly (ethylene glycol) diacrylate (PEGDA) to demonstrate the production of biphasic nanoparticles with nanoscale anisotropy (Supplementary Table S2). These platforms were subsequently advanced to create functional biomaterials with differential crosslinking densities using poly (ethylene oxide) (PEO) and dextran, enabling pH-sensitive, decoupled release kinetics where one hemisphere degrades selectively while the other remains stable (Bhaskar et al., 2010). The capacity of spatial segregation has been further utilized for improving the performance of imaging, such as using magnetic iron oxide (Fe₃O₄) and rare-earth fluorophores in Janus poly (lactic-co-glycolic acid) (PLGA) microspheres to enhance fluorescent intensity, which was increased by a factor of 3.2 (Li et al., 2018). Furthermore, asymmetric surface functionalization via copper-click chemistry has allowed for the selective PEGylation of one compartment, significantly improving the circulation time of PLGA-based Janus nanoparticles in murine models for vascular targeting (Rahmani et al., 2015). Recent innovations have integrated electrospray with microfluidic platforms to enhance structural control and the biocompatibility of the process. Using dextran and polyethylene glycol (PEG) together, an all-aqueous three-phase system (A3PS) is developed to generate continuous flow of the solvent-free Janus droplets as a biocompatible template for encapsulating labile biologics, such as liposomes (Song et al., 2021). Gelatin methacryloyl (GelMA) and hyaluronic acid methacryloyl (HAMA) have been used to develop bio-inspired hydrogel microcarriers for bone regeneration, where microcarriers release different drugs in a staggered manner: first, vascular endothelial growth factor (VEGF) for promoting angiogenesis, and, later, bone morphogenetic protein-2 (BMP-2) for promoting osteogenesis (Yang et al., 2023). Alongside, fabrication methods have been tested as well, such as side-by-side electrospinning/electrospraying to obtain bilayer polycaprolactone (PCL) and poly (L-lactic acid) (PLLA) dressings doped with magnesium oxide (MgO) nanoparticles to modulate macrophage polarization and accelerate wound healing (Zhou T. et al., 2024). Moreover, the rational electroformation of block copolymers have resulted in the production of Janus giant unilamellar vesicles (JGUVs) with laterally phase-separated membranes as synthetic cell mimetics (Equy et al., 2025).

Unlike other techniques for fabrication, electrospray-assisted phase separation has several advantages, such as complete compartmental independence, high monodispersity, and mild fabrication conditions that preserve the bioactivity of sensitive growth factors (Yang et al., 2023). However, there are certain limitations such as the low throughput of producing a single droplet, and the instability of the Janus morphology when the interfacial tensions are not well controlled (Saqib et al., 2024). Overall, electrospray offers precise control over Janus particle architecture, enabling versatile biomedical applications.

2.3 Bioactive glass-integrated Janus systems

Bioactive Glass (BG), originally developed by Larry Hench in 1969 with the 45S5 composition, represents a class of surface-reactive inorganic biomaterials that bond to living tissues through the formation of a Hydroxycarbonate Apatite (HCA) layer (Hench et al., 1971; Jones, 2015). These materials are usually made up of a network of silica, phosphate or borate with alkali or alkaline earth oxides such as sodium oxide (Na₂O) and calcium oxide (CaO) (Madival and Rajiv, 2026). In terms of bioactivity, the mechanism is based on the fast exchange of sodium and calcium ions with physiological fluid to form a silanol surface layer that enables the growth of amorphous calcium phosphate (ACP) particles, and eventually on the formation of hydroxycarbonate apatite (HCA) layer similar to that of bone (Thavornyutikarn et al., 2019). In addition to bonding, BGs also promote tissue regeneration at the genetic level by upregulating the genes associated with osteoblast proliferation and differentiation (El-Rashidy et al., 2017). Additionally, the development of Mesoporous Bioactive Glass (MBG) has improved these properties, by offering high specific surface areas and ordered pore structures for the delivery of therapeutic ions and drugs (Vallet-Regí et al., 2022). These glasses are also integrated into Janus biomaterial systems, which are characterized by spatial asymmetry in their morphology, composition, or function, and are used to create “all-in-one” platforms that can meet complex clinical requirements (Liu J. et al., 2026; Mao J. et al., 2026). Unlike traditional homogeneous scaffolds, bioactive glass-integrated Janus systems leverage spatial programming to separate contradictory functions, such as infection control and tissue regeneration (Liu J. et al., 2026). One of the most common fabrication techniques of these systems is sequential or bilayer electrospinning, commonly known as “A-and-B” method, which is used to create membranes with different hydrophilic/hydrophobic gradients (Liu J. et al., 2026) (Table 1). For example, Huang et al. (2025) developed a Janus wound dressing combining an antibacterial hydrophobic PLA/PCL layer with a hydrophilic borosilicate BG-loaded layer that promoted angiogenesis and wound healing. Likewise, Mao J. et al. (2026) fabricated a bilayer membrane for cranial periosteum repair, where a bioactive glass-containing hydrophilic layer stimulated mineralization while a hydrophobic PCL layer enabled directional cerebrospinal fluid transport. Alternative fabrication methods have further expanded BG-based Janus systems. Magnetron sputtering combined with sol–gel processing generated self-propelled Mesoporous Bioactive Glass (MBG)/Platinum (Pt) nanomotors for dentinal tubule therapy (Wu et al., 2023), whereas in situ sol–gel processing with selective surface protection produced temperature-responsive Janus sponges for hemorrhage control. Other approaches, including freeze casting, biomineralization, and pulsed laser deposition, have been used to fabricate multiscale Janus architectures with enhanced osteogenic and epithelial regeneration properties (Li Y. Y. et al., 2026). The biological performance of these systems is strongly influenced by the type of bioactive glass employed. Mesoporous bioactive glasses (MBGs) are particularly attractive because of their high drug-loading capacity and tunable composition. Doping with therapeutic ions, such as Cu²⁺ or Ga³⁺, enhances angiogenesis and antibacterial activity while promoting M2 macrophage polarization and tissue repair (Liu et al., 2025). Overall, BG-integrated Janus membranes provide multifunctional platforms that combine antibacterial activity, immunomodulation, angiogenesis, and osteogenesis, making them highly promising for wound healing and bone regeneration (Liu J. et al., 2026).

TABLE 1. Representative studies on bioactive glass-based Janus particles: composition, fabrication methods, and biomedical applications.

Despite their considerable potential, bioactive glass (BG)-integrated Janus systems face several challenges that may limit their functional reliability and clinical translation. The complexity of manufacturing still poses a significant challenge, especially in terms of obtaining well-defined asymmetry, good bonding between the interfaces, and scalable production with minimal residual solvent contamination (Chen et al., 2026). Interfacial instability may arise from BG dissolution, which can weaken glass–matrix interactions and compromise long-term Janus integrity (Chen et al., 2026). Furthermore, the mechanical mismatch and brittleness of BG with the softer polymeric or hydrogel compartments could limit the use of these materials under mechanical stress (Shendage et al., 2026). Precise control of ion-release kinetics is also critical, as excessive dissolution may cause burst release and local alkalinization, whereas insufficient release may reduce therapeutic efficacy (Moghanian et al., 2026). BG composition, structure, crystallinity, surface area, and processing conditions further influence these release profiles (Moghanian et al., 2026). To ensure the biocompatibility and safety of the device, several parameters need to be considered, including pH-dependent cytotoxicity, hemocompatibility, and dopant toxicokinetics (Kendra et al., 2026). Finally, limited standardized testing, long-term in vivo validation, and regulatory frameworks continue to hinder reliable comparison and clinical translation (Moghanian et al., 2026).

BG-integrated asymmetric architectures can coordinate antibacterial, immunomodulatory, angiogenic, and osteogenic function in space, while manufacturing complexity, interfacial stability, ion-release control, and long-term safety will remain important challenges to translation.

2.4 Layer-by-layer and multilayer self-assembled thin films

2.4.1 Surface-engineered Janus coatings

Surface-engineered Janus coatings represent a conceptually distinct paradigm in biomaterial design, one in which the two opposing faces of a substrate whether a planar membrane, a particulate carrier, or a three-dimensional scaffold are endowed with chemically or biologically disparate properties in a spatially controlled, asymmetric fashion (Rowland et al., 2024) (Figure 4). Unlike conventional homogeneous surface treatments that apply identical functionalities across an entire device, Janus coatings deliberately exploit interfacial asymmetry to simultaneously address conflicting biological demands: osteoinduction on one face while preventing soft-tissue invasion on the other; pro-adhesive topology on the luminal surface of a vascular conduit while an anti-thrombotic chemistry coats the abluminal layer; or cell-instructive topographical cues on one side of a dural patch while anti-adhesive properties prevent fibrotic encapsulation on the contralateral face (Bi et al., 2025).

Layer-by-Layer (LbL) assembly and multilayer self-assembly have emerged as the foundational fabrication strategies underpinning the majority of surface-engineered Janus coatings described in the regenerative medicine literature (Bi et al., 2025; Na et al., 2025). The process of fabrication begins with the preparation and surface activation of the substrate, which must present a charged or chemically reactive interface capable of engaging the first building block through electrostatic attraction, hydrogen bonding, or covalent anchoring (Rowland et al., 2024). The substrate is immersed in, or coated by brushing, spraying, or spin-coating with, a solution containing the first polyelectrolyte or functional material, which adsorbs until surface saturation. After rinsing, the substrate is exposed to a complementary building block, typically oppositely charged in classical polyelectrolyte LbL assembly, reversing the surface charge for the next deposition cycle. Repeating this adsorption–rinsing sequence enables precise control over film thickness, composition, and stratified architecture, with each bilayer typically adding one to tens of nanometres. Janus asymmetry is achieved by selectively coating one face while protecting the opposite side, either through masking strategies, such as Polymer-on-Polymer Stamping (POPS) (Cayre et al., 2003; Li et al., 2005), and Wetting-Engendered Templated Self-Assembly (WETS) (Rowland et al., 2024) or by sequential face-specific deposition on planar membranes, where the substrate geometry confines each coating to a single surface. Once the target multilayer architecture is assembled, an optional crosslinking or annealing step may be applied to stabilise the film against ionic-strength-induced delamination or mechanical fatigue under physiological conditions (Park et al., 2018). The result is a stratified asymmetric construct in which each face possesses a distinct molecular identity, while the thickness, composition, and bioactivity of each layer can be precisely tailored by controlling the deposition cycles and assembly conditions.

LbL assembly offers several advantages, including operational simplicity, low cost, aqueous processing, and the ability to conformally coat substrates with complex geometries. However, its widespread application is limited by time-consuming deposition cycles, scalability issues, and limited mechanical stability (Park et al., 2018). To overcome these limitations, Zhang Y. et al. (2023) combined unidirectional evaporation-induced pore formation with the self-assembly of a metal–phenolic network (MPN) composed of tannic acid and Cu²⁺. Angiogenesis, osteogenic differentiation and M2 macrophage polarization were induced, while simultaneously preserving the barrier role of the dense PLA layer, thus improving the periodontal bone regeneration in vivo. Similarly, Ma Z. et al. (2024) developed a sandwich-structured Janus membrane using shear flow-driven LbL assembly, integrating an antibacterial chitosan (CHI)/poly (acrylic acid) (PAA) layer with an osteogenic calcium phosphate (CaP)@collagen (COL)/polyethylene glycol (PEG) (CaP@COL/PEG) layer. This multifunctional membrane inhibited E. coli and Staphylococcus aureus while significantly improving bone regeneration, highlighting the potential of combining antimicrobial and osteoinductive functions within a single construct. The versatility of post-fabrication face-selective functionalization also extends to soft tissue repair. Bi et al. (2025) engineered a Janus small intestinal submucosa membrane for spinal dural regeneration by combining LbL surface activation with PDMS-templated dual-sided coating. The microgrooved inner surface promoted fibroblast alignment and anti-inflammatory macrophage polarization, whereas the outer HAMA-SilMA coating prevented protein adsorption and epidural fibrosis. Similar concepts have been applied to implantable devices. Cheon et al. (2021) engineered an asymmetric magnesium-alloy Janus stent by combining a sirolimus-loaded poly (ether imide) (PEI) coating with selective tantalum ion implantation on the luminal surface. This dual-functional design promoted endothelialization on the luminal side while inhibiting smooth muscle cell proliferation on the sirolimus-eluting abluminal side.

Likewise, Na et al. (2025) developed a biodegradable urethral stent integrating magnesium ion-mediated tissue regeneration with externally triggered antibacterial drug release, illustrating the potential of Janus coatings to provide spatially and temporally controlled therapeutic functions.

Surface-engineered Janus coatings allow the spatial coupling of complementary and opposing biological functions on each side of a substrate and provide control of interfacial interactions in regenerative and implantable systems. Face-selective assembly of LbL and other approaches offers flexible methods for programming surface chemistry, bioactivity, and architecture. Their ability to functionalize the surface in multiple steps and limited mechanical and manufacturing scalability, however, may limit their wider application, thereby driving the need for alternative strategies to directly include anisotropy into the biomaterial architecture.

2.4.2 Gradient and compartmentalized thin films

Gradient and compartmentalised thin films constitute a sophisticated class of Janus biomaterials specifically engineered to replicate the inherent compositional and structural anisotropy of biological interfaces (Lei et al., 2022). Whereas surface-engineered Janus coatings generate asymmetry through post-fabrication modification of a pre-existing substrate, gradient and compartmentalized architectures intrinsically encode spatial variation during film formation. This is achieved either through continuous gradients in composition, morphology, or physicochemical properties across the membrane thickness, or through a stratified multilayer configuration that enables functional compartmentalization within a single construct. The distinction is not only surface modification, but also a structurally coherent gradient, rather than two distinct surfaces separated by a structural substrate, gradient films provide a continuous, mechanically coherent transition between opposing biological environments, such as mimicking osteochondral interface gradients, bone–skin interface, and skin–water interface (Du et al., 2025). The main benefits of these materials over traditional homogeneous films are their ability to actively direct the behavior of elongated cells, create spatiotemporal control over drug delivery and adjust local mechanotransductive signals via different stiffness and porosity, which make them attractive for guided bone regeneration, wound management, and osteochondral repair (Pan H. et al., 2026). These architecturally complex systems are built with a variety of sophisticated fabricating techniques, that all take advantage of different physicochemical forces to induce spatial asymmetries. Among the most widely adopted is LbL assembly, which affords nanometric control over film thickness and composition through the iterative, electrostatically driven adsorption of complementary building blocks (Sailer and Barrett, 2012). Reactive LbL (rLbL) approaches, such as those employing aza-Michael addition chemistry, extend this precision further, enabling the introduction of mechanical and thickness gradients with covalent interlayer stability that classical physisorption-based multilayers cannot achieve (Özenler et al., 2023). Within the diagnostic extension of this paradigm, Khalid et al. (2025) employed layer-by-layer self-assembled multilayers (LbL-SAMu) to fabricate gradient thin films for molecular magnetic resonance imaging (MRI) imaging. Alternating deposition of positively charged poly (dimethyl diallyl ammonium chloride) (PDADMAC) and negatively charged Janus magnetic-polystyrene colloids coated with amino dextran generated films with a controlled gradient in colloid distribution, surface hydrophilicity, and T2-weighted MRI contrast. Compared with homogeneous colloidal suspensions, the gradient architecture improved colloid dispersion and surface exposure, highlighting its potential as a molecular probe for lab-on-chip and point-of-care MRI diagnostics. Beyond diagnostic applications, sequential layer-by-layer electrospinning has become a widely adopted strategy for fabricating multilayer Janus membranes with tailored wettability gradients and porosity. Using this approach, Qi et al. (2025) developed a multilayer wound dressing that enabled rapid unidirectional exudate transport (24 s) through a self-pumping wettability gradient while providing sustained antibacterial activity against Staphylococcus aureus and E. coli, together with excellent mechanical strength and biocompatibility. An innovative alternative to both layer-by-layer assembly and electrospinning is the electro-sorting approach developed by Lei et al. (2024), in which mild electrical stimulation induces the spontaneous self-organization of a homogeneous chitosan/gelatin mixture into a Janus film with integrated compositional and microstructural gradients in a single fabrication step. This membrane is made of a dense chitosan-rich component that would provide mechanical support and inhibit the invasion of fibroblasts while at the same time allowing the adhesion and differentiation of osteoblasts in a porous gelatin-rich component, making it a promising material for guided bone regeneration. In addition to this approach, vapour-phase deposition is a one-step process to create a strong Janus film without the restriction of pH and ionic strength given by conventional LbL assembly. Ye and Mao, (2017) fabricated mechanically reinforced Janus films via initiated chemical vapour deposition (iCVD), with a hydrophobic and a hydrophilic surface separated by a crosslinked PEGDA core. These films were also found to be very patternable and conformal to complex substrates. Another versatile approach is interface-directed self-assembly at the air–water interface. On the other hand, Zhang et al. (2014) self-assembled ultrathin free-standing Janus films composed of azopyridine derivatives (PDAB) and PAA, while Zhao et al. (2023) compressed PEG-b-PNPE to produce asymmetric films with nanometre-thick membranes of different wettability for drug delivery and biosensing. Recently, multifunctional gradient Janus membranes, which combine antibacterial and regenerative properties, have been developed. To achieve this, Wang et al. (2024) loaded the MB@ZIF-8@HA nanocomposites into a polyurethane membrane, which was then applied to inhibit E. coli and S. aureus and promote periodontal regeneration by simultaneously delivering a photodynamic therapy (PDT) effect and a sustained release of Zn²⁺. Similarly, Song et al. (2024) created a P(VDF-TrFE)/BaTiO₃ Janus membrane that produced ROS via electrical stimulation on the surface, which was effective in inhibiting S. aureus biofilms and promoting the healing of wounds and periodontal tissues.

The following fabrication strategies can produce four major types of functional gradients that have different roles in regenerative medicine. Chemical and wettability gradients can create “liquid diodes”, which allows for unidirectional flow of fluid in the presence of Laplace pressure gradients formed by uneven wettability profiles, thus providing passive, self-pumping exudate management (Zhou et al., 2026). Second, mechanical and stiffness gradients in the membrane, induced by spatial modulation of crosslinking density throughout the thickness, control stem cell behaviour, mechanotransduction and lineage commitment in a manner that is not possible with homogenous substrates (Özenler et al., 2023). Third, topographical gradients, which occur when the pore size distribution on one side of the gradient is greater than the other, both repel the infiltration of unwanted cells and favor the vascularization and colonization by progenitor cells on the other side (Yan et al., 2025). Finally, biological gradients are a particularly advanced form of spatial functionalization, where cells are guided to migrate, angiogenesis, and lineage-specific differentiation is achieved throughout the construct with the incorporation of bioactive molecules and growth factors such as BMP-2 and VEGF in a spatially controlled manner (Du et al., 2025).

Gradient and compartmentalised Janus films provide an excellent strategy to combine spatially programmed chemical, mechanical, topographical and biological cues into one architecture. By controlling these gradients during fabrication, the important properties of heterogeneous tissue interfaces are reproduced and directional transport, cell guidance and targeted therapeutic activity can be achieved. However, achieving such precise and reproducible gradients which are also structurally stable and scalable to manufacturing is still difficult, highlighting the need for more integrated fabrication strategies.

Overall, Janus gradients enable multifunctional and spatially controlled biomaterial interfaces, although their reproducible and scalable fabrication remains challenging.

2.5 Dual-interface regenerative membranes

Dual-interface regenerative membranes are made by preparing two layers with different chemical and structural characteristics and by stabilizing the interface between the two layers so that they do not delaminate, with each of the two layers having a particular function as a regenerative layer. Layer-by-layer or sequential assembly allows for control of the number, thickness and chemistry of the layers, and is usually followed by a dense barrier side and a cell-instructive side (Irawan et al., 2021; Li Y. Y. et al., 2026). The interface can also be precisely arranged as sequentially or simultaneously assembled collagen and hydroxyapatite, which adjusts the mechanical coupling and mass transport of the interface (Irawan et al., 2021). Bioinks and co-printing such as stereolithography (SLA) and digital light processing (DLP) allow for the spatially controlled deposition of different bioinks in specific areas, creating programmed barrier and porous/bioreactive domains that mimic complex tissue transitions (Jamalpour et al., 2022; Zhou et al., 2025). However, electrospinning and subsequent hybridization or postassembly bonding can also be used to construct fibrous layers that can be combined with materials like gelatin, hydroxyapatite, magnesium (Mg), or graphene oxide (GO) to fineshine their mechanical support, cellular infiltration, antibacterial activity, and degradation (dos Santos et al., 2020; Zhang H. et al., 2026). The junction between layers is further strengthened and delamination in hydrated environments can be prevented by using in-situ interfacial crosslinking or coating, such as aminolysis, UV curing, or covalent bonding (Deng et al., 2026; Zhang R. et al., 2024). In general, fabrication is based on the principle of functional zoning that is, a dense layer hinders undesirable soft-tissue infiltration, while a porous or bioactive layer encourages cell adhesion, osteogenesis, nutrient transport, and tissue integration (Bee and Hamid, 2022; Zhang H. et al., 2026). This performance is not only influenced by the material properties of each layer but also by the interfacial strength of the layers, the sequence of the layers, the hydrophilicity and the pore structure and architecture, all of which contribute to the structural integrity and the biological selectivity of the resulting performance (dos Santos et al., 2020; Du et al., 2026; Jamalpour et al., 2022). However, increasing architectural complexity can improve multifunctionality while simultaneously increasing fabrication time, interface defects, and manufacturing challenges (Cheng and Yang, 2019; Zhan et al., 2025). The ultimate goal of the development of dual-interface membranes is to successfully design a stable, functional interface between them that maintains the specific functions of each interface during the dynamic and hydrated environment of tissue healing (Du et al., 2026; Zhang R. et al., 2024).

An asymmetric guided bone regeneration (GBR) membrane composed of a dense hydrophobic PCL layer and a porous osteogenic nHA/PCL/PEG layer was developed to prevent soft-tissue invasion while promoting osteogenic differentiation and new bone formation. The membrane also provided sufficient mechanical strength to stabilize bone grafts (Pan P. et al., 2024). Similarly, Luo et al. (2022) fabricated an electroactive Janus membrane integrating a P(VDF-TrFE) layer with a polymethyl methacrylate (PMMA) substrate. The electroactive surface promoted osteogenesis and M2 macrophage polarization, whereas the PMMA side prevented fibroblast infiltration, illustrating the potential of electrically active Janus membranes for guided tissue regeneration. More recently, Kim et al. (2026) developed a multilayer PCL Janus membrane enabling the spatial delivery of platelet-derived growth factor-BB (PDGF-BB) and BMP-2 from opposite interfaces, thereby promoting soft-tissue integration and bone regeneration through sustained growth factor release. These studies demonstrate the evolution of dual-interface regenerative membranes from passive barrier systems to multifunctional Janus platforms integrating barrier protection, osteogenesis, immunomodulation, antibacterial activity, and controlled therapeutic delivery. By generating spatially distinct biological microenvironments, these membranes represent a promising strategy for regenerating complex tissue interfaces.

2.6 Core–shell and biphasic Janus hydrogels

As shown in Figure 5A, core–shell and biphasic Janus hydrogels achieve spatial compartmentalization through distinct architectures, enabling sustained drug release or dual, independently tailored functionalities, respectively. The production of core-shell and Janus hydrogels relies on specialized techniques that control droplet assembly and chemical cross-linking. Microfluidic systems are frequently employed due to their high degree of control over particle size, shape, and internal organization (Zhu et al., 2024). This scalable approach facilitates the creation of multicompartment, Janus-shaped, and core-shell structures by manipulating emulsion droplets (Cao et al., 2025). By utilizing Aqueous two-phase systems (ATPS) droplets, researchers can achieve spontaneous cross-linking of tetra-PEG macromonomers. Rapid reactions at specific pH levels (7.4–7.8) yield core-shell structures, whereas slower reactions at lower pH (≤7.0) result in a structural shift toward Janus microparticles (Watanabe et al., 2019). Charge-driven processes, such as extruding cationic cellulose nanofibrils into a PAA bath, enable the formation of millimeter-sized core-shell spheroidal hydrogels (Calabrese et al., 2020).

Ding et al. (2025) developed magnetic Janus hydrogel microrobots to promote the regeneration of the gradient structure at the tendon–bone interface (TBI). In their approach, alginate pre-gel solutions were injected through independent coaxial needles, while nitrogen gas flowing through the surrounding annular space generated a shear force that detached pre-gel droplets from the needle tips (Figure 5B). The detached droplets were subsequently collected in a calcium chloride (CaCl₂) bath, where rapid ionic crosslinking resulted in the formation of hydrogel microspheres. The size of the microspheres could be precisely controlled by adjusting the nitrogen gas flow rate. Under an external magnetic field, the Janus hydrogel microrobots exhibited controlled orientation and locomotion, enabling them to align with the native tendon–bone interface and accurately conform to its complex gradient architecture (Figure 5C).

Core-shell structures feature a central component enclosed by a distinct outer layer, while Janus hydrogels are characterized by biphasic or asymmetric architectures (Yan et al., 2025). Core-shell often consist of a liquid-like core protected by a semipermeable, solid-like hydrogel shell. Some designs incorporate hydrophobic magnetic particles within the core to enhance material properties. Janus architectures possess asymmetric surface designs, often featuring two distinct sides or phases (Pan M. et al., 2024). This asymmetry allows for the functionalization of different surfaces, such as a basal surface for tissue integration and an apical surface for anti-fouling or anti-adhesion, mimicking natural biological barriers (Pan M. et al., 2024).

Huang W. et al. (2023) developed a Janus-inspired core–shell hydrogel for the programmed release of melatonin to promote postoperative bone tumor reconstruction. The fabrication process began with the preparation of the hydrogel core by injecting a pre-gel solution containing 5% methacrylated hyaluronic acid (HAMA) and 5% Pluronic F127 diacrylate (F127DA), with or without 5 mM melatonin, into a 3D-printed core–shell mold. The core precursor was subsequently photocrosslinked under 405 nm light for 1 min to obtain a stable hydrogel. The solidified core was then transferred onto a 3D-printed base and surrounded by a fence-shaped mold. A 10% gelatin methacryloyl (GelMA) solution containing 100 mM melatonin was injected into the remaining space to form the shell, followed by a second 1 min photocrosslinking step. After mold removal, the uncovered bottom region was filled with additional GelMA and subjected to a final photocrosslinking process to completely seal the core–shell structure (Figure 6A). The Janus-inspired core–shell hydrogel enabled a programmed, sequential release of melatonin (Figure 6B). The outer GelMA shell degraded rapidly, releasing a high concentration of melatonin during the early stage to induce apoptosis of residual B16 tumor cells. Subsequently, the HAMA/F127DA core provided a sustained low-dose release of melatonin, which promoted the osteogenic differentiation of bone marrow mesenchymal stem cells (BMSCs). This sequential therapeutic strategy effectively shifted from an initial antitumor phase to a bone regeneration phase while simultaneously providing structural support to the bone defect site.

However, though the core–shell or biphasic Janus hydrogels have multiple functional applications, there are still significant challenges in their interface stability, fabrication complexity, scale up and functional long-term reliability. Poor interfacial adhesion can cause delamination, slippage between layers or loss of structural asymmetry during swelling, cyclic stress, or ageing (Ma et al., 2025). Concurrently, various fabrication methods involve complex and multiple processing steps and demand compositional, viscous, flow, or interfacial control, which reduces reproducibility and complexity in production processes (Chellappan et al., 2026). Scalable and standardized fabrication therefore remains a critical unmet need, particularly for preserving precise layer thickness, composition, and asymmetric architecture across batches and production scales (Chellappan et al., 2026). Future efforts should focus on simplified one-step, microfluidic, 3D-printing, and monolithic approaches that combine structural precision with high-throughput manufacturing (Wu et al., 2026). Furthermore, better resistance to swelling, dehydration, thermal/chemical stress, and repeated mechanical loading should be ensured to maintain the structural and functional integrity under realistic conditions (Chao et al., 2025). For biomedical translation, long-term biocompatibility, biodegradation, in vivo stability, and functional retention also require more comprehensive validation (Xue et al., 2025). In conclusion, to make these asymmetric hydrogels a platform for reliable long-term validation and for clinical or industrial use, they must be combined with more powerful interfacial engineering, scalable fabrication, mechanical strength, and rigorous long-term validation (Guo W. et al., 2025).

Within hydrated biomaterials, spatial compartmentalization can be used to separately control biochemical, mechanical and therapeutic properties ranging from specific interactions within tissue to programmed release of drugs. This results in a core–shell and biphasic architecture being ideal for regenerative applications where both complex tissue interfaces and temporally coordinated therapeutic needs are present. There are still challenges to be addressed including interfacial integrity, reproducible compartmentalization, scalability and long term stability, which demand fabrication strategies that integrate architectural precision, mechanical durability and translational feasibility. In general, the principle of spatial compartmentalization is a robust design strategy to engineer biomaterials that have multiple biological and therapeutic functions.

2.7 3D/4D bioprinted Janus constructs

3D printing, also known as additive manufacturing, is an advanced fabrication technology that enables the layer-by-layer construction of three-dimensional objects from computer-aided design (CAD) models (Yang Y. et al., 2025). The 3D printing technology has several significant advantages over traditional manufacturing methods, such as the ability to create custom structures that can be designed for specific functions, the efficient use of materials and reduction in waste, and the precision and accuracy of the manufacturing process when producing geometrically complex structures (Dang et al., 2021; Thiruchandran et al., 2025). The features have made 3D printing a promising platform for the creation of multifunctional biomaterials, especially in the fields of regenerative medicine and tissue engineering.

Over the past few years, 3D printing is gaining a lot of interest in the field of Janus hydrogel systems. Compared to traditional approaches that struggle to create well-defined dual-faced hydrogel structures, 3D printing allows for the precise control of spatial organization of different materials within a single construct. This capability is especially useful if each face of the Janus hydrogels is modified with a different biological or physicochemical function. The 3D-printed Janus hydrogels can combine multiple functionalities on a single platform by selecting or modifying the appropriate bioinks, by incorporating appropriate functional nanoparticles, and by optimizing mechanically robust and biocompatible polymer networks. Their multifunctionality makes them very useful for biomedicine, biosensing, tissue engineering and regenerative therapy (Gao et al., 2022; Guo et al., 2023).

Despite these advantages, several challenges still limit the broader translation of 3D-printed Janus hydrogel systems. These include the relatively high cost of printing equipment and biomaterials, time-consuming post-processing steps, and the limited availability of printable bioinks that simultaneously meet requirements of printability, biocompatibility, mechanical stability, and biological functionality.

In addition, fabrication defects such as delamination, excessive porosity, weak interfacial bonding, and surface roughness may occur during printing, which can affect the structural integrity and reproducibility of the final constructs. These limitations remain important barriers to scalable and clinically applicable production (Liu et al., 2021; Zhou X. X. et al., 2024).

Several recent studies have demonstrated the potential of 3D-printed Janus hydrogel platforms in regenerative medicine (Huang D. et al., 2023). designed a 3D printed Janus piezoelectric hydrogel patch for wound healing applications. As illustrated in Figure 7A, these bilayer design gave complementary therapeutic functions. The top layer was a poly (ethylene glycol) diacrylate hydrogel filled with gold nanoparticle-decorated barium titanate to allow the generation of reactive oxygen species via ultrasound without the leakage of nanomaterials. GelMA loaded with vascular endothelial growth factor was used in the lower layer to promote cell proliferation, angiogenesis and tissue regeneration. The dual-function design emphasizes the importance of Janus design for the simultaneous delivery of antimicrobial protection and regenerative stimulation in a single wound dressing platform.

A significant advance has also been reported in cardiac tissue repair through the development of hierarchical porous Janus hydrogel myocardial patches (JHPMPs) by Liu Z. et al. (2026). This asymmetric patch was designed to address a major clinical challenge in cardiac surgery, achieving strong adhesion to the injured myocardium while preventing postoperative thoracic adhesions. The patch was fabricated by a multimaterial bioprinting approach consisting of a porous GelMA/PEO microgel active adhesive layer with induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs) and a HAMA anti-adhesive layer facing the thoracic cavity. The adhesive bioactive layer supports nutrient diffusion, cell migration, vascularization, and myocardial integration, whereas the anti-adhesive layer limits undesirable tissue attachment. Under beating-heart conditions, this Janus configuration enables suture-free functional integration, reduces therapeutic cell leakage, and decreases infarct size and fibrosis compared with conventional treatments. As shown in Figure 7B, the Janus architecture is therefore essential for targeted, safe, and mechanically stable myocardial repair.

In addition to wound applications and cardiovascular, Janus hydrogel systems are being investigated for soft actuator and surgical repair applications. Wu et al. (2026) proposed a Janus polyelectrolyte hydrogel of modified chitosan and sodium alginate. The hydrogel was synthesized in one pot, via electrohydrodynamic printing, and in situ photopolymerization, with a seamless interface, high mechanical strength, ionic conductivity and efficient electro-actuation. It is characterized by pH-programmable reversible bidirectional bending, which allows it to bend in either direction when it needs to do so due to the acidity/alkalinity of the environment. This platform has been demonstrated in an underwater soft gripper, a biomimetic flower, and has a great potential in the field of soft robotics, bioinspired systems, and biomedical applications.

Similarly, Hao et al. (2026) developed a 3D-printed composite Janus hydrogel patch composed of PVA/SPH for abdominal wall reconstruction. The patch integrates a mechanically strong outer poly (vinyl alcohol) (PVA) layer with a 3D-printed inner SPH layer exhibiting antibacterial activity against S. aureus. This Janus organization simultaneously provides mechanical reinforcement, antibacterial protection, biocompatibility, and anti-adhesion performance. In vivo results showed reduced postoperative adhesions and enhanced tissue regeneration compared with commercial polypropylene meshes, indicating the potential of this strategy for abdominal hernia repair.

In cardiac medicine, Janus-structured patches can provide unilateral adhesiveness, promoting integration with injured myocardial tissue while preventing thoracic adhesions and supporting angiogenesis and cardiomyocyte maturation (Liu Z. et al., 2026). In gynecologic surgery, similar asymmetric constructs may serve as advanced anti-adhesion barriers, provided that they meet strict requirements for biocompatibility, reproductive safety, and long-term tissue compatibility (Fazel Anvari-Yazdi et al., 2025).

In parallel with advances in 3D printing, 4D bioprinting has emerged as a promising evolution of additive manufacturing, introducing time-dependent structural and functional adaptability into printed biomaterials. Unlike conventional 3D-printed constructs, 4D-bioprinted systems incorporate stimulus-responsive materials capable of undergoing programmed changes in shape, physicochemical properties, or biological function in response to environmental cues, including moisture, temperature, pH, light, and enzymatic activity (Faber et al., 2024). This dynamic behavior is particularly attractive for regenerative medicine, where biomaterials must adapt to the evolving biochemical and mechanical conditions of the physiological environment. In this context, combining Janus architecture with 4D bioprinting provides an additional level of spatial and temporal control, enabling distinct responses to be encoded within different regions of the same construct.

Several studies have demonstrated the potential of this strategy for programmable, multi-responsive actuation. Parimita et al. (2025) described a 4D-printed Janus bilayer hydrogel structure exhibiting pH-responsive, bidirectional actuation. The asymmetry between the two solvent-responsive hydrogel layers, fabricated by Direct-Ink Writing (DIW), drives reversible shape morphing upon immersion, with a non-morphing point at pH 7. Strong interlayer adhesion was achieved without chemical surface modification, yielding an interfacial toughness of 71.8 J/m² and no delamination during actuation. Optimal printing was obtained at a speed of 5 mm/s, extrusion pressure of 5–6 bar, nozzle diameter of 0.5 mm, and ink viscosity in the range of 10²–10⁵ Pa s. These results demonstrate a robust, programmable Janus actuator with potential use in smart valves.

Beyond pH responsiveness, Wang et al. (2021) described a 4D-printed PNIPAM–PEGDA hydrogel bilayer exhibiting multi-stimuli-responsive shape morphing, fabricated via 3D printing and made “4D” through its post-printing, time-dependent bending behavior. The Janus-type asymmetry between the two layers, with PNIPAM being thermo- and solvent-responsive (cononsolvency effect in ethanol–water mixtures) while PEGDA remains insensitive to both stimuli, drives directional and angle-dependent bending of the bilayer upon changes in temperature or solvent composition. To add a third stimulus, Fe₃O₄ nanoparticles were selectively incorporated into the PEGDA layer, endowing the structure with magnetic responsiveness and enabling remote-controlled deformation and motion under an external magnetic field. This work demonstrates how compositional asymmetry in a bilayer hydrogel can be engineered to achieve programmable, multi-responsive 4D actuation.

A complementary approach was reported by Narupai et al. (2021) who developed a 3D/4D-printed protein-based hydrogel system designed for biodegradable, multi-stimuli-responsive shape morphing, addressing the poor biodegradability of existing shape-morphing materials. The strategy uses methacrylated bovine serum albumin (MA–BSA) as a biodegradable building block, combined with N-isopropylacrylamide or 2-dimethylaminoethyl methacrylate to form shear-thinning Pickering emulsion gels suitable for direct ink writing (DIW) of multi-layered structures. This introduces a Janus-type functional asymmetry, as poly (N-isopropylacrylamide) confers temperature-responsiveness while poly (dimethylaminoethyl methacrylate) confers pH-responsiveness, enabling reversible shape changes depending on the environment. A distinctive feature is the enzyme-triggered, irreversible transformation driven by BSA network degradation, adding permanent structural change on top of the reversible responses.

In a regenerative medicine context, these developments are especially significant for wound healing, as the local environment is continually changing in terms of moisture, temperature, pH, enzymatic activity and bacterial load (Figure 8). These dynamic cues could be used for 4D printed Janus scaffolds to adapt their shape or adjust their function once in place. The two complementary interfaces, one surface hydrophilic and bioactive with a pro-cell adhesion and tissue integration and angiogenesis effect, while the other surface hydrophobic and antimicrobial, with barrier protection and local drug delivery or stimuli-controlled. This kind of coordinated, spatiotemporally arranged functionality might at the same time foster biointegration, antimicrobial protection, guided tissue regeneration, vascularization and wound closure. Therefore, the coupling of Janus’ spatial asymmetry and 4D temporal responsiveness is a promising design paradigm for next-generation adaptive wound dressings and regenerative scaffolds that can dynamically engage in the evolving wound microenvironment.

3D/4D printing opens up design possibilities for Janus hydrogels as it allows precise spatial organization and, more and more, programming of temporal responses in a single construct. The combination of spatial asymmetry and dynamic adaptability provides new chances to coordinate tissue integration, barrier protection, antimicrobial activity and stimuli-responsive therapeutic functions in evolving biological environments. However, it is still a challenge to obtain reliable interfaces of two or more materials, long-term performance and scaling bioprinting. To take these programmable Janus systems a step closer towards clinically relevant applications, further developments in bioink design, integration at the interfaces, printing accuracy and dynamic functional validation are required. Overall, 3D/4D printing enables programmable Janus hydrogels with spatial and temporal control for dynamic tissue regeneration.

3 Functional properties

3.1 Controlled and sequential drug delivery systems with temporal release and multi-agents delivery strategies

Janus biomaterials are transforming regenerative medicine by enabling the integration of different drugs or various concentrations of the same therapeutic agent in distinct areas of the same scaffold. This physical separation provides important functional and biological advantages by preventing interference between the loaded drugs, reducing the metabolic burden, and enabling the generation of controlled biological gradients that closely mimic complex tissue transitions, such as those found at the tendon–bone interface (Ding et al., 2025; Huang W. et al., 2023; Yang D. et al., 2025).

What is also interesting in this architecture is the temporal release profiles, which enable the biomaterial to communicate with the body in the correct chronological order. Many Janus systems, for example, are intended for sequential or ‘burst/sustained’ drug delivery. With this functionality, the biomaterial can initiate burst release to manage urgent needs, like infection, and then be followed by sustained release for long-term tissue repair (Huang W. et al., 2023). Janus acoustically responsive scaffolds (ARSs) exemplify this phenomenon, where one side of the scaffold can be triggered by ultrasound, resulting in a steady, triphasic release over the period of days, while the other side of the scaffold delivers a rapid, pulsatile dose only when needed. These programmed kinetics guarantee correct medication dosage on time when the body is moving to the next phase of healing (Xiao et al., 2025).

The (Collagen-DCMC@Curcumin/Chlorhexidine, CDCC) membrane in guided bone regeneration is a good example of a multi-agent drug delivery strategy. The Janus structure has a dense layer containing the antibacterial agent chlorhexidine (CHX) that works quickly to protect against bacteria, while curcumin-loaded nanomicelles enable sustained release of curcumin for up to 60 days, thereby supporting prolonged anti-inflammatory activity. At the same time, the porous side filled nano-hydroxyapatite creates a welcoming environment for bone-forming cells (Yang D. et al., 2025). Another example, designed by Huang W. et al. (2023), is the Mel@Gel/Mel@HF hydrogel for bone tumor treatment after surgery, which releases a high dose of melatonin from the fast-degrading shell to destroy cancer cells, while the core provides a sustained release of a low dose of melatonin for 10 weeks to promote bone repair. These systems can also facilitate the regeneration of complex tissue interfaces, in addition to promoting bone regeneration, through ion-mediated biological cues. For example, the Janus hydrogel microrobot developed by Ding et al. (2025), can be magnetically aligned at a rotator cuff tear, with the magnesium-loaded side oriented toward the bone and the zinc-loaded side toward the tendon. This spatially defined mineral gradient is maintained for more than 21 days, thereby synchronously stimulating the regeneration of both bone and tendons tissus. These Janus platforms shift medicine from passive support to active, intelligent instructions, whether it involves delivering growth factors in a timed sequence or through ROS-responsive linkers that only release antioxidants when the inflammation is detected (Pan X. et al., 2026; Xiao et al., 2025).

The advances underscore Janus biomaterials’ capability to fuse spatial localization of drugs with temporal programming of release to coordinate therapeutic functions with the phases of tissue healing. These systems can simultaneously address long-term tissue regeneration needs while meeting acute demands like infection or inflammation by compartmentalizing the agent or concentrations and/or designing release rates. Collectively, Janus biomaterials offer a powerful strategy for synchronizing spatially localized and temporally controlled therapeutic functions with tissue healing.

3.2 Dual-sided functionality: protective vs. regenerative interfaces

The Janus membrane paradigm has become a new all-in-one solution for the development of next-generation biomaterials in the field of tissue engineering with the combination of two fundamentally different interfaces in one structure. The asymmetric design enables simultaneous management of both conflicting clinical needs, a protective interface to prevent external interference at the injury site and a regenerative interface to stimulate tissue repair (Li Y. Y. et al., 2026; Liu J. et al., 2026).

The protective interface of Janus material is usually smooth, dense, and hydrophobic. Which act as a physical and chemical barrier (Liu J. et al., 2026; Pan P. et al., 2024). In guided bone regeneration (GBR), this face serves as an important space-maintainer since the rapid migration of fibroblasts and epithelial cells into the defect site would hinder the slower process of osteogenesis. This layer is often made from bioinert, structurally dense materials like polycaprolactone (PCL) or polylactic acid (PLA) (Liu J. et al., 2026). This interface can also include anti-fouling surface characteristics, such as hydrophobic surfaces or zwitterionic polymer coatings that prevent non-specific protein adsorption and cell attachment. These features are crucial in preventing pathological fibrous connections, such as adhesions of the peritoneum and soft tissue, and in reducing foreign body reactions (Gao et al., 2026).

On the other hand, the interface of regeneration is rough, porous, and hydrophilic, enabling a deep integration with the host tissue (Pan P. et al., 2024). The face is engineered to control cell behaviour by multiple mechanisms and creates a nano-topography similar to the natural extracellular matrix (ECM), which provides essential anchorage points for osteoblasts and mesenchymal stem cells (MSCs). This side can act as a reservoir for bioactive substances including hydroxyapatite (Hap), collagen, or growth factors, including bone morphogenetic protein (BMP-2) and vascular endothelial growth factor (VEGF) that can stimulate key signaling pathways, promoting the deposition of mineralized matrix and the development of angiogenesis (Liu J. et al., 2026). Moreover, in a sutureless repair, the regeneration interface can utilize immediate bioadhesive mechanisms that involve rapid incorporation of water into the interface, thus forming physical crosslinks, followed by covalent bonding with the tissue surface (Gao et al., 2026).

Spatially directing bioactivity to support regeneration and reducing undesirable interactions, Janus membranes replicate the protective–regenerative architecture of the periosteum to provide an integrated solution for complex and infection-prone defects.

3.3 Antimicrobial and anti-adhesive properties

Infection remains a major challenge in regenerative medicine, particularly in orthopedic implants and chronic wounds. At the biomaterial–tissue interface, bacterial colonization, host immune responses, and material degradation can interact and contribute to persistent inflammation and device failure (Arciola et al., 2026). These interconnected processes highlight the limitations of conventional single-function antimicrobial coatings, which primarily target bacterial infection without simultaneously addressing biofilm formation, immune-mediated inflammation, or material stability. Janus biomaterials offer a promising alternative by spatially integrating distinct functions, such as antimicrobial activity and anti-adhesive properties, while preserving cell compatibility on the tissue-facing side (Guo W. et al., 2025) (Figure 9).

3.3.1 Infection control strategies

The antimicrobial face of Janus biomaterials can be obtained by adding biocidal agents such as AgNPs, antimicrobial peptides (AMPs), quaternary ammonium compounds (QACs) or antibiotic loaded nanocarriers (Zhang R. et al., 2025). Of these, AgNPs are the most commonly used, due to their activity against Gram-positive as well as Gram-negative bacteria and their low level of toxicity at low concentrations (Frippiat et al., 2025; Hosny et al., 2026). The methods and approaches used for embedding AgNPs in Janus architectures, however, differ significantly from the latest studies, depending on the focus of the design. Passive AgNP coatings are not always present, but Wang X. et al. (2025) incorporated Ag-armed iron oxide nanoparticles within a magnetically responsive Janus system, allowing for on-demand disruption of biofilms in the presence of an external magnetic field. In contrast, Zhang J. et al. (2026) focused on multifunctionality rather than actuation by incorporating AgNPs with curcumin that was “green synthesized” to provide not only antibacterial activity, but also antioxidant and biofluid-management properties. The difference in design/controllable release versus multifunctional synergy, implies that the course taken by the development of AgNP-based Janus systems are different and the clinical advantages of the two are yet to be conclusively determined, this will require a direct head-to-head comparison (Rai et al., 2022; Xu J. et al., 2024).

AMPs represent an alternative antimicrobial strategy based primarily on membrane disruption, which may reduce the likelihood of resistance compared with conventional antibiotics (Yuan et al., 2025; Zhu et al., 2022). A common barrier with the use of earlier AMP-functionalized materials was the leaching of peptides and their short-term antimicrobial effectiveness, which was overcome by Wang et al. with covalent binding of AMPs onto electrospun nanofiber mats, resulting in durable antimicrobial surfaces with minimal cytotoxicity toward mammalian cells (Wang Z. et al., 2022). In Janus architectures, spatial localization of AMPs can further restrict their activity to the bacteria-facing surface, potentially preserving the biocompatibility of the tissue-facing side (Frippiat et al., 2025).

A third strategy is neither of the AgNP nor AMP-based, instead using an external trigger, not constitutive, for antimicrobial activity. Photothermal and photodynamic Janus designs feature photosensitizers or plasmonic nanostructures on one side that create reactive oxygen species or local heat when excited by light (Meng et al., 2023; Ren et al., 2025). This on-demand activation may reduce prolonged antimicrobial exposure and associated resistance pressure (Singh et al., 2023). However, its clinical translation remains dependent on the feasibility of light delivery, particularly for deep-tissue and internal applications.

Localization of antimicrobial activity can decrease the off-target effects in regenerating tissues. Differences in mechanism of action, release and tissue compatibility still matter, though, for the choice of the appropriate strategy. As a whole, this method provides a potential balance between infection control and tissue repair.

3.3.2 Prevention of biofilm formation

Biofilm formation represents a major challenge in biomaterial-associated infections because biofilm-embedded bacteria exhibit increased resistance to antimicrobial agents and host immune responses (Raouan et al., 2023). Preventing the initial bacterial attachment through surface modification therefore provides a complementary strategy to bacterial killing and may reduce the selective pressure associated with continuous antimicrobial exposure (Belay et al., 2024; Hu et al., 2024).

Zwitterionic polymers, including polysulfobetaine methacrylate (pSBMA) and polycarboxybetaine (pCB), are widely investigated for their anti-adhesive properties. Their highly hydrated surfaces reduce protein adsorption and bacterial attachment through steric and electrostatic mechanisms (He et al., 2025; Sun et al., 2020). In Janus membranes, zwitterionic functionalization can be localized to the bacteria-facing surface while maintaining a cell-adhesive tissue-facing side, thereby combining infection resistance with tissue integration (Han J. et al., 2024). PEG-based coatings provide another anti-fouling strategy, although zwitterionic materials may offer greater chemical stability for certain long-term applications (Xu et al., 2025).

A key advantage of Janus architectures is therefore the spatial separation of anti-adhesive and cell-adhesive functions, overcoming the trade-off commonly observed in homogeneous anti-fouling coatings (Meng et al., 2024). More recently, the combination of anti-adhesive surfaces with low-level antimicrobial agents has enabled synergistic Janus systems capable of both preventing bacterial attachment and eliminating bacteria that remain adherent (Chelu et al., 2025).

Janus anti-biofilm strategies therefore spatially separate bacterial anti-adhesion from tissue integration, while combining antifouling and antimicrobial functions to limit both bacterial colonization and biofilm establishment.

3.4 Fluid and exudate management

Effective exudate management is essential for wound healing, as both excessive and insufficient moisture can impair tissue repair (Malone and Schultz, 2022). Excessive fluid accumulation may cause periwound maceration and promote bacterial growth, whereas insufficient moisture can hinder keratinocyte migration, enzymatic debridement, and growth factor signaling (Mirhaj et al., 2022). Conventional wound dressings often rely on uniform wettability, which limits their ability to simultaneously maintain an optimal moist environment, remove excess exudate, and protect the wound from external contamination. This limitation arises from the mismatch between the homogeneous properties of conventional materials and the spatially dynamic requirements of the wound microenvironment (Mirhaj et al., 2022).

However, this incompatibility can be overcome by designing Janus biomaterials that have opposing wettability gradients in a single platform, allowing for both moisture control and directional fluid transport and selective permeability in a single, integrated structure (Wang X. et al., 2026).

3.4.1 Moisture regulation

Moisture regulation in Janus biomaterials is primarily achieved through differences in wettability between the two surfaces (Ranatunga et al., 2026). A common design is one that includes a hydrophilic inner surface that absorbs exudate and provides a moist healing environment and a hydrophobic outer surface that prevents evaporative loss and contamination from the outside (Cui et al., 2026). Several fabrication strategies have been explored to generate such asymmetry, including electrospinning of bilayer fiber mats, surface modification of preformed membranes, and self-assembly of amphiphilic block copolymers (Tian et al., 2023). These approaches offer different advantages and limitations. Electrospinning provides control over fiber and layer architecture but presents scalability challenges; surface modification is more readily scalable but may result in heterogeneous or unstable functionalization; and block copolymer self-assembly enables molecular-level asymmetry but offers less control over macroscopic pore architecture. Thus, fabrication strategy can directly influence both functional performance and translational feasibility.

These strategies include electrospun Janus membranes, which have been the most experimentally explored. Hydrophilic poly (vinyl alcohol) (PVA) or poly (acrylic acid) (PAA) with a water absorbing property on the wound side has been used with hydrophobic polycaprolactone (PCL) or polyvinylidene fluoride (PVDF) on the outer side showed an excellent moisture balance in wound healing models (Chang Y. et al., 2026). The hydrophilic component could absorb the exudates at a rapid rate, while the hydrophobic one would act both as a moisture barrier and as a physical barrier against external pathogens. Dynamic contact angle measurements, in vitro fluid uptake assays have been proven to show asymmetric wettability of these systems, and animal studies have shown improved rates for wound closure compared to traditional dressings. However, the long-term stability of bilayer structures under repeated hydration–dehydration cycles remain insufficiently investigated.

An alternative strategy to regulate moisture has been developed by attaching thermoresponsive polymers like poly (N-isopropylacrylamide) (pNIPAM) to one side of a Janus dressing. When below its lower critical solution temperature (LCST, ∼32 °C), pNIPAM exists in a hydrophilic and swollen conformation, absorbing fluids, while above this temperature, it collapses into a hydrophobic conformation, further inhibiting fluid uptake in the wound. The thermoresponsive switching mechanism adds a level of self-regulation to the fluid uptake which is something that the static wettability designs do not naturally provide, and could allow the dressing to automatically respond to the changing microenvironment within a wound through its own fluid uptake rather than relying on an external agent (Ahmad, 2023).

Moisture regulation in Janus biomaterials relies on spatially controlled wettability to balance exudate management, hydration, and external protection. Static hydrophilic–hydrophobic designs provide effective moisture partitioning, whereas thermoresponsive systems introduce adaptive control of fluid uptake. However, long-term interfacial stability and reliable switching under physiological conditions remain critical considerations for clinical translation.

3.4.2 Selective permeability

In addition to moisture control, Janus biomaterials can be designed to selectively let certain molecules pass through, such as oxygen, growth factors, or small metabolites, while preventing the passage of other molecules, including bacteria, large proteins, or toxins (Yin et al., 2024). Most importantly, the selectivity is not a single property but rather the composite effect of at least three design parameters that can be independently tunable, which are the pore size, the surface charge and the chemical functionality in each layer of the Janus structure (Zhang J. Y. et al., 2025). This separation is important since optimizing one of these parameters often leads to compromises in others: decreasing pore size to exclude bacteria, for example, may also decrease oxygen diffusion or growth factor transport, while optimizing these other parameters may increase pore size and thus increase the risk of bacteria invading into the pores (Zhang J. Y. et al., 2025).

Gas permeability, particularly oxygen transport, is among the most investigated selective transport properties of Janus wound dressings. Oxygen is essential for cellular respiration, collagen synthesis, and angiogenesis during wound healing (Zhou W. et al., 2024). Janus systems combining gas-permeable silicone or porous hydrophobic outer layers with hydrogel-based inner layers can facilitate oxygen diffusion while maintaining a moist wound interface and limiting external fluid penetration (Nasra et al., 2023; Ye et al., 2024). This bilayer design (gas permeable outer layer and moisture retentive inner layer) is often referred to as simulating the barrier and transport properties of normal skin (Yao et al., 2025). This is a very conceptually attractive analogy, but needs careful consideration: native skin is hierarchically structured, dynamic and metabolically active, and none of the currently existing Janus membranes can reproduce all these characteristics.

One such new and complementary mechanism of permeability control is added by charge selective Janus membranes, which work at the molecular scale (Ge et al., 2023). Such materials can electrostatically anchor and effect-controlled release of negative growth factors such as VEGF and bFGF, with the net surface being positively charged, which directs the growth factor towards the wound bed, while the other surface being neutral or negative, which minimizes the growth factor’s loss to the outside environment (Kharkar et al., 2013). This spatial directionality of bioactive molecule delivery represents a significant conceptual advancement over isotropic delivery systems that rely on growth factors that diffuse uniformly in all directions and have a high percentage of biofactor waste (Hu et al., 2025).

Janus biomaterials serve as a delivery vehicle for the transport of oxygen and biofactors, while preventing unwanted penetration or loss, through their controlled pore architecture, surface charge and interfacial chemistry, and, as such, provide a platform for spatially selective transport. Optimizing the selection, transport efficiency and structural stability is critical to physiological performance.

3.5 Guidance of cellular behavior

The interaction of the implanted biomaterials and host tissues is highly dependent on the interaction of the cells at the interface of the material and the host tissue, which is not passive and one-way (Rompen et al., 2006). The cells not only interact with a passive material surface, but actively remodel, deposit extracellular matrix on, and transfer mechanical forces through the surface, as well as provide physical and chemical signals to direct cell fate. This two-way communication implies that cell adhesion, cell migration, cell proliferation and cell differentiation are not sequential and independent processes but are tightly coupled and highly regulated by the interplay of signals from the extracellular environment (ten Brink et al., 2024). For example, it is important to remember that a surface that promotes optimal adhesion of cells may paradoxically hinder directed cell migration and vice versa; a surface optimized to promote directed cell migration might optimize adhesion too little to support long-term survival of the cells and tissues (Chen et al., 2024). While these intrinsic problems associated with the design of multiple concurrent cellular functions are not always explicitly recognized in the primary literature, they constitute the fundamental problem of biomaterial-guided tissue regeneration.

The key challenge in which Janus biomaterials excel is the distribution of contrasting and complementary signals on opposing sides of the material, rather than the resolution of a tension between one uniform surface and another (ten Brink et al., 2024). Instead of trying to reconcile different requirements on one side, Janus designs integrate each requirement on one side of the material where it is required most, with a different requirement integrated on the other side of the material, such as a tissue-contacting side with cell-adhesive, pro-migratory or induction cues, and a bacterial-repelling or fluid-handling side (Li X. et al., 2026). This spatial programming of cellular signals is a conceptual move from the traditional design of biomaterials where surface properties must be averaged over the material (Han M. et al., 2024).

3.5.1 Cell adhesion, migration, and differentiation

In the case of cell adhesion, integrin-ligand interactions between cell surface receptors and adhesive proteins, which have been deposited on or embedded in the biomaterial surface, mediate the adhesion (Karimi et al., 2018). Adhesion-promoting peptides, like RGD (Arg-Gly-Asp), IKVAV, and YIGSR, can be attached to the surface of the material on the cell-contacting face in order to direct cells to specific integrins and improve cell adhesion. These three peptide sequences, however, are not functionally interchangeable and by clustering them in the biomaterials literature important differences exist in the biological specificity of the peptides: RGD, found in fibronectin, promotes adhesion of multiple cell types by engaging different integrin subtypes, while IKVAV and YIGSR, found in laminin, respectively promote adhesion of neural and epithelial cells through different integrin subtypes. This specificity will have direct impact on Janus scaffold design, as the selection of the adhesion peptide on the cell-contacting face should be tailored to the specific cell population being targeted and not chosen in a generic manner. In the case of skeletal muscle stem cells, Leblanc et al. (2026) showed that adhesion motifs could be discovered in a peptide array screen, which were not predicted using the traditional design logic of RGD-based peptides, suggesting that the assumption that a small number of well-known peptide sequences is enough to be utilized in all tissue engineering applications is incorrect. These adhesive cues are localized to the desired surface by creating a non-adhesive side of the Janus scaffold using anti-fouling chemistry to maintain the functional asymmetry of the Janus architecture.

In addition to the surface design challenge of static adhesion, there is the challenge of cells moving in and out of the surface, a dynamic process unlike static adhesion, which requires that cells not only adhere, but detach and re-adhere in an ordered sequence in a coordinated manner (Cui et al., 2021). To overcome this, Janus scaffolds have been developed that contain asymmetric topographical or chemical gradients that can guide migration in a particular direction, with the migratory cues only on the side where directed cell migration is desired (Lei et al., 2019). Preliminary studies have shown that cells select grooves, ridges, or channels over flat and rough surfaces via contact guidance as a mechanosensitive response, in which cells concentrate their cytoskeletal tension along the grooves, ridges, or channels, thereby biasing lamellipodia extension (Leclech and Villard, 2020). This principle was later expanded by Li et al. to develop bioinspired hierarchical microtextured surfaces that allow both programmed fluid guidance and cell migration to be incorporated into the same topographical design (Li L. et al., 2026).

Perhaps the most challenging use of Janus biomaterial-mediated cellular guidance involves stem cell differentiation, where signals that must be provided to encourage stem cells to differentiate into a specific lineage are context-dependent, and are simultaneously affected by soluble factors, surface chemistry, topography, and substrate stiffness (Keung et al., 2010). Janus biomaterials have been developed to provide lineage specific differentiation signals on one face (stiff, mineralized) and a neutral or supportive face (soft, hydrogel-like, and/or neurogenic, stiff/ECM-coated) (Park et al., 2021). The clinical potential of this strategy is that it can steer mesenchymal stem cells (MSCs) differentiation toward a desired lineage without the addition of exogenous soluble factors, which minimizes the complexity of regulating stem cell therapy and the costs (Liu et al., 2024). This statement, however, is qualified because most of the studies done to support factor-free differentiation on Janus substrates have been done in idealized in vitro settings where adjacent cells, immune factors or system hormones can be controlled in the absence of competing soluble signals (Steward and Kelly, 2015). The relative importance of cues mediated by the substrate in the in vivo environment, where MSCs are simultaneously subjected to a complex mixture of endogenous biochemical cues, is likely to be significantly reduced (Etzenberger and Hernandez, 2026).

Spatially programmed adhesive, migratory, and differentiation cues therefore enable Janus biomaterials to guide cell–material interactions and cell fate while highlighting the need for tissue-specific design and validation under physiologically complex conditions.

3.5.2 Topographical and biochemical cues

Mechanotransduction pathways regulate cell behavior in response to topographical cues, whereby physical surface features such as grooves, pillars, pores, and aligned fibers are translated into intracellular biochemical signals through modulation of cytoskeletal organization and gene expression, ultimately influencing cell fate (Harvey et al., 2013). Topographical anisotropy is achieved in Janus biomaterials by electrospinning aligned nanofibers or patterning the surface with grooves in a direction that causes the cells to align and elongate in a desired direction, whereas the other face has a random or smooth topography which performs an orthogonal function, such as repelling bacterial growth or fluid management (Wang M. L. et al., 2023). This spatial separation of topographical functions is not just a design consideration, but a functional requirement because the topographical features which guide the alignment of cells (sub-micron to micron-scale anisotropic grooves or aligned fibers) cannot be co-localized on a single surface without compromise, as they are structurally incompatible with the isotropic porous architectures used to optimize anti-adhesion of bacteria or fluid transport. The Janus architecture tackles this incompatibility not by compromising on the topography but by dedicating each function to the face on which it is applied, avoiding the interference of other functions (Li Y. Y. et al., 2026).

The most extensively studied nanofiber Janus scaffolds for tissue regeneration have been those of anisotropic tissues, including tendons, ligaments, nerves, and myocardium, whose native architecture is characterized by highly organized cell and matrix arrangements that are directionally oriented and are not readily duplicated by isotropic scaffolds (Zhang J. Y. et al., 2025). Cells grown on aligned nanofiber surfaces develop elongated cells and align parallel to the direction of the nanofibers, which resemble the organization of cells in native anisotropic tissues (Wang et al., 2015). This contact guidance effect has been observed to improve cell alignment as well as the mechanical anisotropy of the tissue engineered as a result, with animal models of nerve repair and tendon regeneration showing enhanced functional outcomes compared to random fiber controls (Wang et al., 2015).

In contrast to topographical signals, biochemical signals that are immobilized in Janus biomaterials trigger one of several receptor-mediated intracellular signaling pathways, not mechanosensitive pathways (Tu and Gao, 2021). The recent development of surface chemistry methods has made it possible to attach multiple bioactives to various faces of a Janus scaffold, thereby generating a spatially defined biochemical landscape that stimulates a coordinated spatial sequence of vascular ingrowth and mineral matrix deposition, particularly in the context of vascularized bone regeneration (Wang J. F. et al., 2025). In particular, heparin affinity binding growth factor delivery platforms stand out as promising tools for achieving sustained and controlled release of both VEGF and BMP-2 from opposing Janus faces with minimal cross-diffusion between sides (Wang J. F. et al., 2025).

Janus architectures therefore spatially decouple anisotropic topographical guidance from localized biochemical signaling, enabling coordinated control of cell organization and tissue-specific regeneration.

3.6 Remote guidance and spatially controlled regeneration

Unlike conventional biomaterials, Janus systems can convert external physical stimuli into localized biological responses, enabling remote activation, targeted positioning, and precise regulation of cellular behavior (Latiyan et al., 2021). Remote localization and activation are primarily achieved by combining structural asymmetry with stimuli-responsive components, including magnetic nanoparticles, piezoelectric materials, or ultrasound-sensitive elements. While most Janus biomaterials rely on their asymmetric compartmentalization to spatially confine biological cues, an increasing number of advanced systems enable non-invasive external control through magnetic fields, ultrasound, or electric fields, allowing therapeutic functions to be activated only at the desired anatomical site (Wang L. et al., 2022). Among these approaches, ultrasound-responsive Janus scaffolds represent one of the most compelling examples of remotely controlled regenerative biomaterials. Camarero-Espinosa and Moroni (2021) developed a 3D-printed piezoelectric Janus scaffold capable of converting externally applied ultrasound into nanoscale mechanical vibrations. This remotely generated nanovibration significantly enhanced the proliferation, extracellular matrix deposition, and osteogenic differentiation of human bone marrow mesenchymal stem cells (hBMSCs) through activation of voltage-gated calcium channels, demonstrating that mechanical stimulation can be delivered non-invasively without direct physical contact.

Similarly, Liang et al. (2026) developed a bilayer Janus electrospun scaffold (KZP@PS/PSPM) for tendon-to-bone regeneration after rotator cuff injury. The piezoelectric PSPM layer converts ultrasound-induced mechanical energy into electrical stimulation, promoting osteogenic differentiation of bone marrow mesenchymal stem cells, while the KZP@PS layer enables stress-responsive release of kartogenin (KGN) and Zn²⁺ ions. This synergistic system enhances immunomodulation, chondrogenesis, and osteogenesis via the ERK1 and PI3K/Akt signaling pathways. In vivo, it reduced early inflammation and significantly improved tendon-to-bone healing, demonstrating the potential of integrating piezoelectric stimulation with spatially controlled drug delivery. Magnetic-field-responsive Janus biomaterials constitute another major strategy for remote guidance. Superparamagnetic components enable scaffolds or particles to align with externally applied magnetic fields, assemble into field-driven superstructures, or migrate along magnetic gradients toward specific anatomical targets (Ding et al., 2025). Beyond localization, magnetic guidance can also regulate scaffold architecture and cellular organization. For example, Wang L. et al. (2022) developed an injectable magnetic nanofiber-hydrogel scaffold whose anisotropic microstructure could be remotely controlled by a magnetic field, promoting three-dimensional cellular alignment and significantly enhancing functional muscle regeneration in volumetric muscle loss models. At the microscale, electrically driven Janus microbots have also demonstrated higher propulsion velocities than magnetically actuated counterparts, resulting in improved intracellular delivery efficiency (Latiyan et al., 2021).

Nevertheless, this is still a small fraction of current regenerative systems based on remotely actuated Janus biomaterials. Although several recent reviews have outlined ultrasound-, magnetic-, electric-, and other stimuli-responsive Janus platforms as an emerging area of research in which external physical addressing is coupled with compartmentalized therapeutic functions, most reported Janus biomaterials still utilize their intrinsic structural asymmetry to a large degree (Mao H. J. et al., 2026).

A major emerging advantage of Janus biomaterials is their potential to combine spatially asymmetric functionality with remote guidance, enabling therapeutic components to be positioned, oriented, or activated at specific anatomical sites without direct manipulation. The two faces of a Janus device in this context are not only structurally different, but their different physicochemical properties can be used in the determination of the response of the material to an external stimulus and of its therapeutic functions spatially presented. This is especially appealing in complex regenerative environments where precise localization and targeting of interactions with tissues are required, and it is implemented remotely.

This concept is highly relevant to GBR, where asymmetric membranes provide complementary barrier and osteogenic functions. A dense layer limits fibroblast infiltration and soft-tissue invasion, whereas the opposite porous and bioactive surface promotes osteoblast adhesion, proliferation, differentiation, and bone ingrowth (Lei et al., 2024).

This architecture is mostly based on the intrinsic structural asymmetry, but its compartmentalised organisation is ideal to incorporate externally-controlled elements, so that the regenerative interface can be placed or orientated in the desired location/positionality relative to the target tissue. Likewise, metal–phenolic acid coated PLA Janus membranes have been endowed with barrier properties, as well as immunomodulatory and angiogenic functions, highlighting the possibility of spatially confined activities to be coordinated within a single asymmetric construct (Zhang Y. et al., 2023).

The relevance of this strategy extends beyond bone regeneration. Janus tendon patches, for instance, integrate an adhesive antioxidative inner surface with an anti-adhesive external layer, thereby establishing directional tissue interactions that can potentially be spatially controlled at the injury site (Zhang Q. et al., 2023). In cartilage regeneration, the spatial confinement of transforming growth factor-β1 (TGF-β1) within an inner Janus nanomatrix creates a localized chondrogenic microenvironment, illustrating how asymmetric compartmentalization can translate spatial positioning into selective biological stimulation (Landolina et al., 2022). Likewise, the sequential antibacterial and regenerative functions of Janus skin dressings and the compartmentalized delivery of hydrophilic and hydrophobic therapeutics in spinal cord nanoplatforms highlight the value of spatially controlled therapeutic presentation (Song et al., 2026). Importantly, these examples indicate that remote guidance should not be viewed as an isolated actuation mechanism, but as a means of controlling where, how, and which Janus face interacts with the target tissue. When combined with magnetic, optical, acoustic, or other externally responsive components, the inherent asymmetry of Janus biomaterials can therefore transform passive compartmentalization into actively directed and spatially programmable regeneration. This convergence between structural anisotropy and remote control offers a particularly promising route toward minimally invasive targeting, site-specific drug delivery, and dynamic regulation of regenerative microenvironments in anatomically complex tissues.

Stimuli-responsive components extend Janus asymmetry from passive spatial compartmentalization to remotely programmable biological control. By integrating the directional architecture and magnetic, acoustic, electrical or other external stimuli, these systems can be used to control the interaction of therapeutic functions with target tissues in time, place and manner. Their broader translation will depend on precise actuation, safety, spatial selectivity, and reliable performance under physiological conditions.

3.7 Metabolic modulation of tissue regeneration

Although Janus biomaterials were initially designed to provide spatially separated multifunctionality, increasing evidence indicates that their regenerative efficacy is fundamentally mediated by metabolic reprogramming. These asymmetric biomaterials actively shape the bioenergetics, redox homeostasis and immunometabolism of cells to establish a regenerative microenvironment that facilitates tissue repair, as opposed to merely being scaffolds or localized drug delivery systems (Wang F. et al., 2026). A growing body of evidence demonstrates that Janus biomaterials can directly regulate the metabolism of stem and progenitor cells to promote tissue regeneration. In bone tissue engineering, Cheng X. et al. (2025) showed that a Janus bone membrane enhances oxidative phosphorylation (OXPHOS) in bone marrow mesenchymal stem cells (BMSCs), identifying this metabolic shift as the key mechanism driving osteogenic differentiation. The membrane maintains high levels of mitochondrial respiration, not glycolytic metabolism, thus assuring adequate bioenergetic support for bone formation and affirms the importance of oxidative metabolism in determining stem cell fate.

In addition to stem-cell metabolism, Janus biomaterials also modulate regeneration by controlling macrophage immunometabolism, a key role in orchestrating inflammation and tissue repair. Chang D. et al. (2026) created a collagen-based Janus membrane which can regulate the glucose metabolism and mitophagy in macrophages for the treatment of infected diabetic bone defects. This metabolic activation results in a decrease in intracellular reactive oxygen species (ROS), in the restoration of mitochondrial function and in a polarization toward the pro-regenerative M2 phenotype, setting the immunological conditions for bone repair.

Similarly, Tao et al. (2025) showed that a Janus exosome patch for soft-tissue regeneration simultaneously activates multiple energy-producing signaling pathways, such as those of the adenosine monophosphate-activated protein kinase (AMPK) and the tricarboxylic acid (TCA) cycle, and other mitochondrial metabolic pathways, while inhibiting inflammatory pathways. The coordinated metabolic activation drives polarization to M2 macrophages and profoundly boosts tissue reconstruction, highlighting the tight links between metabolic activities and immune regulation in regeneration. In recent studies, it is also shown that the metabolic modulation can be combined with a multifunctional structural design. Yang D. et al. (2025) developed a multifunctional Janus CDCC membrane for guided bone regeneration with a biomimetic asymmetric architecture and sequential drug release. The dense outer layer prevents bacterial invasion and soft-tissue infiltration, while the porous nHAP-enriched inner layer promotes osteoblast adhesion, proliferation, and differentiation. DCMC crosslinking improves mechanical strength, whereas chlorhexidine (CHX) provides rapid antibacterial activity. Sustained curcumin release modulates macrophage polarization toward the pro-regenerative M2 phenotype via Interleukin-1 (IL-1) and TGF-β signaling, creating an osteoimmunomodulatory microenvironment that supports mesenchymal stem cell osteogenesis even under infectious conditions. This strategy demonstrates how structural asymmetry, antimicrobial protection, and immune modulation synergistically enhance bone regeneration.

Another approach is to tap the dynamic metabolic regulation using environmentally responsive catalytic systems. Han et al. (2026) developed pH-responsive Janus high-entropy alloy (HEA) nanozymes that adapt their catalytic activities to the wound microenvironment. Under acidic infectious conditions, they generate ROS through oxidase- and peroxidase-like activities, effectively eradicating multidrug-resistant bacteria and disrupting biofilms. As physiological pH is restored, they switch to catalase- and superoxide dismutase-like activities, scavenging excess ROS, restoring redox homeostasis, and promoting 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase 3 (PFKFB3)-mediated glycolysis. This transition promotes remodeling of the extracellular matrix, polarization of M2 macrophages, angiogenesis, collagen deposition, and chronic wound healing and indicates that Janus nanozymes could be used as multifunctional candidates for antimicrobial therapy, metabolic regulation and immune modulation.

Metabolic modulation has also emerged as a promising strategy for repairing highly energy-demanding tissues such as the myocardium. Lv et al. (2026) developed a Janus cardiac patch that delivers functional mitochondria to infarcted myocardium, restoring mitochondrial respiration, adenosine triphosphate (ATP) production, and cellular bioenergetics. This metabolic reprogramming enhances myocardial regeneration, while the asymmetric architecture prevents postoperative tissue adhesions, highlighting the potential of metabolism-centered Janus biomaterials for cardiac repair. Collectively, these studies demonstrate that Janus biomaterials promote tissue regeneration through complementary metabolic mechanisms, including mitochondrial bioenergetics, macrophage immunometabolism, glycolytic regulation, and redox homeostasis. In addition, Janus platforms can incorporate metabolic regulators through controlled ion delivery (e.g., Mg²⁺, Zn²⁺, Cu²⁺, Ca²⁺, and phosphate), oxygen-generating or oxygen-releasing components that alleviate hypoxia, and ROS-responsive systems that dynamically balance oxidative stress during tissue repair (Chang D. et al., 2026; Li Z. et al., 2025). Their asymmetric architecture also enables temporal compartmentalization of biological signals, allowing immunomodulatory cues to precede osteogenic or regenerative signals, thereby reproducing the natural sequence of tissue healing events (Cheng X. et al., 2025). While the hallmark of Janus biomaterials remains their asymmetric multifunctional architecture, recent advances clearly demonstrate that metabolic reprogramming constitutes the mechanistic foundation underlying their regenerative performance. By integrating spatially controlled bioactive functions with precise regulation of cellular metabolism, Janus biomaterials are evolving from conventional multifunctional scaffolds into intelligent metabolism-driven regenerative platforms, offering new opportunities for engineering complex tissue repair across bone, soft tissue, skin, and cardiac applications (Wang F. et al., 2026).

By coordinating mitochondrial bioenergetics, glycolysis, redox balance, and immunometabolism with spatially and temporally confined cues, Janus systems can actively shape the regenerative microenvironment. This shift toward metabolism-directed design positions cellular bioenergetics as a key mechanistic dimension of next-generation regenerative biomaterials.

4 Applications in regenerative medicine

The asymmetric, compartmentalized structure of Janus biomaterials is not an aesthetic curiosity of materials engineering; it is a direct structural solution to a problem that plagues almost every tissue-repair scenario in the clinic: namely, that the two faces of an implanted material are almost never asked to do the same job. A wound dressing needs to repel bacteria from the outside, while wicking exudate and delivering bioactive cues from the inside. A bone-regeneration membrane must prevent fibrous connective tissue from growing in one surface and allow osteoprogenitor cells to grow on the other. A tendon patch must glide without friction against the surrounding sheath while tightly adhering to the injured fiber bundle underneath. Janus platforms, in contrast, spatially separate the demands, with each function being assigned to the layer, phase, or compartment best suited to deliver it. Conventional, chemically homogeneous scaffolds are forced into an unsatisfying compromise between these opposite demands. Here we will discuss how that design logic has been translated into measurable regenerative outcomes across six clinical domains including cutaneous wound healing, guided bone regeneration, periodontal and guided tissue regeneration, tendon and ligament repair, postoperative bone tumor reconstruction and the direct modulation of stem cell fate synthesizing the mechanistic rationale, representative platforms and translational hurdles that define the current state of the field. Representative examples of these Janus biomaterial platforms, together with their compositions, fabrication strategies, asymmetric functionalities, and regenerative medicine applications, are summarized in Supplementary Table S3.

4.1 Cutaneous wound healing

4.1.1 Acute and chronic wounds

The skin restoration research provides perhaps the most mature demonstration of Janus design logic, partly because the wound bed itself is inherently asymmetric: a moist, protein-rich interior to be kept hydrated and biologically active, and an exterior to be sealed against desiccation, mechanical insult, and microbial ingress. This duality is directly exploited in electrospun bilayer and multilayer nanofiber membranes where a hydrophobic, mechanically protective outer layer is combined with a hydrophilic, bioactive inner layer that imbibes exudate and promotes keratinocyte attachment. A transparent Janus nanofiber membrane with one side of hydrophobic polycaprolactone and the other of hydrophilic ethylene–vinyl alcohol has been demonstrated to provide high optical transparency for visual wound monitoring, fast fluid absorption, chitosan-mediated antimicrobial activity, and enhanced keratinocyte migration and clotting in vitro (Kuddushi et al., 2024). Related cellular bilayer constructs consisting of bioactive calcium silicate promote directional cell migration and upregulate angiogenic and myofibroblast markers in vivo associated with faster epidermal closure (Wang J. et al., 2025). Amphiphilic Janus membranes have been designed to go beyond a passive barrier and to deliver two pharmacologically distinct agents, an antibacterial and an anti-inflammatory drug, along a controllable gradient from opposite faces, treating infection control and inflammatory resolution as sequential rather than competing objectives (Shi et al., 2023). In-depth analyses of the field now list Janus electrospun membranes for skin, bone, abdominal wall, tendon, and uterus repair, demonstrating how the asymmetric-membrane concept has evolved from a one-off design to a generalizable platform.

Chronic and difficult-to-heal wounds, burns, pressure ulcers, and diabetic foot ulcers impose an additional requirement: sustained, self-regulated management of excess exudate without frequent dressing changes. Biomimetic gradient wettability Janus membranes derived from cactus-thorn structure provide unidirectional “water-diode” drainage, removing fluid from the wound bed while simultaneously enabling light-triggered photothermal and photodynamic sterilization at the exposed face, a synergy that was shown to dramatically enhance healing in diabetic wound models where persistent exudate and infection usually hinder repair (Wen et al., 2026; Zhang et al., 2022). Similar photothermal and photodynamic antibacterial strategies have also been incorporated in Janus membranes consisting of a hydrophilic bacteriostatic inner layer and a hydrophobic near-infrared-responsive outer layer to produce synergistic bactericidal effects on resistant bacteria while maintaining a moist healing microenvironment underneath (Cheng Y. et al., 2025). Unidirectional water-transport membranes with pH-responsive color-changing indicators extend this logic further, allowing the dressing itself to signal infection status non-invasively, a feature of particular value for chronic wounds that are monitored infrequently (Guo K. et al., 2025).

Skin regeneration exemplifies how Janus asymmetry can integrate moisture regulation, antimicrobial protection, directional transport, and tissue repair within a single dressing. The incorporation of responsive and self-monitoring functions further enables adaptation to the dynamic wound microenvironment.

4.1.2 Infection-associated wounds

Where infection is the dominant clinical concern, contaminated burns, ulcerated diabetic wounds, and surgical site infections. Janus architectures allow antimicrobial payloads to be concentrated at the tissue environment interface without diffusing into, and disrupting, the regenerative layer beneath. Drug-eluting Janus nanofibers combining ciprofloxacin with AgNPs have demonstrated rapid, near-complete drug release and superior antibacterial performance against both Gram-positive and Gram-negative pathogens relative to single-layer analogues (Kotteeswaran et al., 2024). This spatial separation of antimicrobial and regenerative function is a recurring theme across the wound-healing literature and anticipates the same design principle seen later in periodontal and tendon applications, where infection control and tissue ingrowth must likewise be decoupled rather than superimposed. Janus architectures therefore offer a versatile platform for coordinating effective infection control with localized tissue regeneration, addressing the complex therapeutic demands of wounds in which antimicrobial activity and tissue repair must occur in a carefully balanced manner.

4.2 Bone regeneration and guided bone regeneration (GBR)

4.2.1 Critical-size bone defects

Guided bone regeneration relies on a barrier membrane that performs two mutually exclusive tasks at once: excluding fast-migrating fibroblasts and epithelial cells from the defect while leaving space and biochemical support for the comparatively slow process of osteogenesis. Conventional collagen membranes such as Bio-Gide® satisfy the barrier requirement adequately but lack the bioactivity and immunomodulatory capacity to accelerate healing in compromised defects. Janus collagen-based membranes address this gap by combining a dense, soft-tissue-facing barrier layer with a porous, bone-facing layer that promotes mesenchymal stem cell infiltration, proliferation, and osteogenic differentiation through active regulation of the local immune microenvironment; in direct comparison, such membranes have outperformed Bio-Gide® in rat calvarial defect models (Yang D. et al., 2025). In infected or pathologically compromised defects, the clinically relevant “worst case” for GBR asymmetric bacterial cellulose/MXene membranes maintain a dense cell-exclusion layer alongside a porous osteogenic layer while conferring the mechanical robustness needed for surgical handling and a degradation rate matched to the bone-repair timeline (Wang B. et al., 2023). Electrodeposited collagen Janus membranes extend this concept to diabetic and infected calvarial models, where an electrodeposited dense barrier is paired with a porous repair layer that modulates macrophage metabolism toward an anti-inflammatory M2 phenotype, sustaining barrier integrity and pro-regenerative signaling simultaneously under adverse physiological conditions (Chang D. et al., 2026).

Functionally graded Janus membranes assembled via layer-by-layer self-assembly for example, a smooth, hydrophobic polycaprolactone isolation layer bonded to a rough, hydrophilic nanohydroxyapatite/polycaprolactone/polyethylene glycol osteogenic layer have demonstrated the capacity to resist soft-tissue invasion on one face while upregulating alkaline phosphatase expression, RUNX2 signaling, and matrix mineralization on the other, translating into superior new bone formation and long-term space maintenance in vivo (Pan P. et al., 2024). The most recent generation of these platforms incorporates hierarchical, biologically inspired architectures including Bouligand-patterned compact layers reinforced with amorphous calcium phosphate to reconcile mechanical strength with osteoconductivity within a single continuous membrane, reporting simultaneous gains in barrier performance and bone regeneration in cranial defect models (Li Y. Y. et al., 2026). Analogous asymmetric strategies have been adapted for anatomically demanding, non-load-bearing applications such as skull-base reconstruction after transsphenoidal surgery, where a hydrophilic, polydopamine-functionalized osteogenic layer is paired with a hydrophobic polycaprolactone layer to simultaneously seal against cerebrospinal fluid leakage and promote local bone formation (Xia et al., 2023).

Janus GBR membranes reconcile barrier protection with osteogenic regeneration by spatially assigning complementary functions to opposing interfaces within a single construct.

4.2.2 Sequential growth factor delivery strategies

Because bone healing proceeds through overlapping but temporally distinct phases, inflammation, matrix deposition, and mineralization of several Janus platforms have been engineered to decouple degradation kinetics from bioactivity so that barrier protection persists even as the interior compartment resorbs and releases its regenerative cargo. A spatiotemporally layered Janus hydrogel produced by sequential photocuring maintains a dense, fully protective outer phase while its loose inner phase supports sustained osteoconductivity; metabolomic analysis of this system has linked its regenerative effect to reprogramming of lipid metabolism in bone marrow mesenchymal stem cells, offering a mechanistic account for why compartmentalized delivery outperforms bolus dosing of osteogenic cues (Lu et al., 2025).

In sum, these results suggest that the power of Janus architecture in the GBR is not just to perform two functions within a single material, but to control the temporal evolution of each function independently.

Janus architecture thus moves the concept of GBR beyond the spatial functional separation, enabling barrier protection and regeneration to take place on separate, tunable timelines. This spatiotemporal decoupling is more suitable to the sequential requirements of bone healing than are the established synchronized or bolus delivery systems.

4.3 Periodontal and guided tissue regeneration (GTR)

Periodontal defects present a spatially compact but functionally complex regenerative challenge, requiring simultaneous exclusion of rapidly proliferating gingival epithelium and fibroblasts, promotion of periodontal ligament and alveolar bone regeneration, and control of a bacterially dense oral microenvironment, three demands that Janus GTR membranes have been specifically engineered to separate across a single bilayer. Bioinspired polyurethane membranes fabricated by spontaneous microphase separation position an antibacterial Gemini quaternary ammonium salt at the air-contact surface while enriching the tissue-contact surface with bioactive dopamine, yielding a smooth, cell-repellent outer face that suppresses fibroblast migration alongside a rough, mineral-promoting inner face that supports osteoblast adhesion and antibacterial protection against common oral pathogens such as Staphylococcus aureus and Staphylococcus mutans (He et al., 2022). A related electrospun bilayer polyurethane fibrous membrane applies the same dopamine/quaternary-ammonium-salt pairing and confirms, in a rat periodontal defect model, that the dopamine-enriched face accelerates mesenchymal stem cell growth and mineralization while the antibacterial face limits fibroblast adhesion, together producing significantly improved periodontal defect regeneration in vivo (Lin et al., 2023).

Metal–phenolic and mineralized nanointerfaces have further expanded the bioactivity achievable on the bone-facing side of periodontal Janus membranes. A Janus porous polylactic acid membrane bearing a versatile metal–phenolic nanocoating on its porous face has been shown to suppress the pro-inflammatory activation of macrophages, promote endothelial angiogenesis, and enhance osteogenic differentiation of human periodontal ligament stem cells, while its dense face preserves conventional barrier function; a combination validated in a rat periodontal bone defect model (Zhang Y. et al., 2023). Gradient-pore membranes loaded with methylene-blue-functionalized zeolitic imidazolate frameworks (MB@ZIF-8) alongside hydroxyapatite have coupled a rough, cell-supportive layer with a smooth, tissue-isolating layer to deliver early reactive-oxygen-species-mediated antibacterial action and sustained zinc-ion release, reporting antibacterial rates above 80% against common periodontal pathogens together with favorable surgical handling (Wang et al., 2024). Chitin-based Janus hydrogels functionalized with copper ions and polydopamine on the antibacterial face and gelatin–hydroxyapatite on the osteogenic face have outperformed Bio-Gide® on cement-enamel junction outcomes in rodent models, while dual-functional immunomodulatory Janus nanofibrous membranes have been purpose-built to address the more hostile microenvironment of diabetic periodontitis, where persistent inflammation and impaired osteogenesis routinely blunt the efficacy of conventional GTR membranes (Huang et al., 2024; Wang F. et al., 2026). Taken together, this body of work has recently consolidated the dual-function Janus membranes for periodontal and bone regeneration which illustrates a maturing consensus that the future of GTR lies in membranes that actively regulate the local immune and osteogenic environment rather than merely occlude it (Li Y. et al., 2025).

Periodontal regeneration highlights the ability of Janus membranes to spatially coordinate barrier exclusion, antimicrobial defense, and osteogenic–immunomodulatory activity within the confined periodontal defect. This shift from passive exclusion toward active microenvironmental regulation represents a key advance in GTR design.

4.4 Tendon and ligament repair

Tendon and ligament healing confronts a design problem distinct from bone or skin: the repaired tissue must glide, under load, past adjacent structures without forming the peritendinous adhesions that are the leading cause of poor functional outcomes after tendon surgery. Janus patches resolve this by pairing an anti-adhesive, low-friction outer face presented to the surrounding sheath and soft tissue with an adhesive, bioactive inner face applied directly to the repaired tendon (Xu L. et al., 2024). A dual-layer Janus patch combining a lubricated, antifouling poly (2-methylacryloxyethyl phosphocholine)-modified nanomembrane with a fibrin-loaded chemotactic fiber layer reduced in vitro cell adhesion by over 92% and motion friction by nearly 80%, and in vivo, suppressed adhesion formation via the TGF-β/Smad signaling axis while simultaneously promoting tendon maturation, a demonstration that inhibiting exogenous (adhesion-forming) healing and promoting endogenous (intrinsic tendon) healing can be pursued as complementary, spatially separated goals within one device (Xie et al., 2024). Mechanically adaptive Janus hydrogels built for tendons subjected to large, repetitive strain pair a bio-repelling polyurethane outer layer, which resists adhesion and reduces reoperation risk, with an inner catechol-functionalized layer that suppresses local inflammation and inhibits synechia formation while withstanding cyclic mechanical loading through strain-induced crystallization (Zhang Q. et al., 2023).

Multi-compartment fiber architectures have pushed this concept beyond a simple bilayer. Tri-section Janus nanofibers produced by three-fluid side-by-side electrospinning distribute beeswax, quercetin, and ketoprofen into three discrete, eccentrically arranged compartments, each with an independently tunable release profile, enhancing anti-adhesive performance in proportion to the hydrophobic beeswax content while preserving the mechanical properties needed to support the healing tendon (Tan et al., 2025). Complementary designs pair a mechanically robust, anti-adhesive poly-l-lactic acid outer layer with an inner electrospun hydrogel functionalized with zinc oxide nanoparticles and tannic acid, delivering combined antioxidative, anti-inflammatory, and antibacterial action directly at the repair site thus addressing the early postoperative inflammatory cascade increasingly recognized as a driver of subsequent adhesion (Huang W. et al., 2023). A parallel line of work on Janus Tough Adhesives applies unilateral tissue adhesion chemistry such that the patch bonds firmly to the tendon on one face while remaining non-adhesive on the other, targeting both mechanical fixation and controlled, spatially confined drug delivery in a single construct (Tang et al., 2022). Broader reviews of tendon and ligament tissue-engineering biomaterials now identify Janus and core–shell architectures as a distinguishing feature separating next-generation constructs from earlier, functionally homogeneous scaffolds, particularly for their ability to reconcile anti-adhesive and pro-regenerative demands that were previously treated as mutually exclusive design goals (Wang S. et al., 2025).

Tendon and ligament repair illustrates the distinctive value of Janus asymmetry in reconciling low-friction protection with localized tissue adhesion and regeneration. By spatially separating these otherwise competing functions, Janus patches can simultaneously limit peritendinous adhesion and support tendon maturation under repetitive mechanical loading.

4.5 Postoperative bone tumor reconstruction

Reconstruction after resection of osteosarcoma and other primary bone tumors poses a uniquely adversarial design problem: the implanted material must eliminate any residual malignant cells in the immediate postoperative period while, over a longer time course, supporting the same osteogenic processes that chemotherapy and radiotherapy tend to suppress. Sequencing these two objectives rather than superimposing them has become the defining strategy of Janus-inspired bone-tumor scaffolds. A Janus-inspired core–shell hydrogel scaffold has been designed to release melatonin at two distinct concentrations from spatially separated compartments: a high initial dose sufficient to suppress residual tumor cell growth in the shell, followed by a lower, sustained dose from the core that instead promotes osteogenic differentiation once the tumoricidal window has passed, illustrating how a single molecule can be repurposed for opposing therapeutic goals purely through differential, compartmentalized dosing (Zhang H. et al., 2024). Some other works on bioactive and drug-eluting scaffolds for osteosarcoma have also emphasize that effective postoperative reconstruction depends on scaffolds capable of an initial burst release of chemotherapeutic or cytotoxic agents to clear residual disease, followed by a sustained release of osteogenic ions or growth factors timed to avoid suppressing the very mesenchymal stem cells and osteoblasts responsible for subsequent bone repair (Baron et al., 2023; Zhao et al., 2021).

This temporal decoupling matters clinically because chemotherapeutic agents such as cisplatin, doxorubicin, and methotrexate while necessary to control local and metastatic recurrence are directly cytotoxic to the osteoprogenitor populations needed for defect repair, and mesenchymal stem/stromal cells introduced to accelerate bone regeneration after tumor excision must therefore be shielded from residual drug exposure or introduced only after the antitumor phase has concluded (Xu et al., 2026). A work on bifunctional scaffold frame this challenge explicitly as a balancing act between oncotherapy and regeneration, and increasingly point to compartmentalized, Janus-type release architectures capable of running an antitumor and a pro-osteogenic program on independent schedules within the same implant as the most promising route toward scaffolds that serve simultaneously as local cancer therapeutics and functional bone grafts (Zhao et al., 2021).

Temporally programmed Janus architectures offer a means to coordinate tumor eradication with subsequent bone regeneration while minimizing interference between these opposing therapeutic requirements.

4.6 Stem cell modulation and tissue engineering

Across each of the applications above, the regenerative benefit of a Janus scaffold is ultimately mediated by how it reshapes the local stem cell microenvironment: stem cells interpret topographical, chemical, and mechanical cues presented by a biomaterial and translate them into differentiation decisions, and asymmetric materials are, in effect, a means of presenting two different instructional environments to the same cell population within a single, spatially continuous device (Fisher et al., 2010; Jang and Kim, 2010). Extending this principle deliberately rather than as a byproduct of barrier design represents an emerging Frontier for the field. In the GBR literature, the osteoconductive Janus hydrogel described earlier has been shown to reprogram lipid metabolism in bone marrow mesenchymal stem cells as its dominant mechanistic pathway to enhanced osteogenic differentiation, a finding that moves beyond descriptive accounts of “improved bone formation” toward a defined molecular route by which compartmentalized materials steer stem cell fate (Lu et al., 2025). More broadly, biomaterial-based control of stem cell differentiation has been shown to operate through soluble growth factor gradients, adhesion-ligand density, and substrate mechanics, all of which can, in principle, be spatially patterned across the two faces of a Janus construct to drive distinct lineage commitments, for example, osteogenic differentiation on one face and a complementary phenotype, such as an immunomodulatory or vascular-supportive state, on the other within a single implanted device (Shi et al., 2023).

The stem cell niche itself is a naturally asymmetric structure, with mesenchymal stromal cells showing graded differentiation behavior according to their proximity to the endosteal surface and comparable positional gradients documented in other adult stem cell compartments, which lends direct biological precedent to engineering asymmetry into synthetic regenerative materials rather than treating it as an incidental structural feature (Shi et al., 2023). As Janus platforms continue to mature from passive bilayer barriers toward actively instructive, metabolically engaged materials, the explicit design of dual, spatially segregated stem cell microenvironments rather than simply dual mechanical or antibacterial functions is likely to define the next-generation of regenerative constructs across all of the tissue systems discussed in this section. Thus, spatially programmed stem cell microenvironments represent a key mechanism through which Janus biomaterials regulate cell fate and enhance tissue regeneration.

5 Current limitations and barriers to clinical translation

The clinical translation of Janus biomaterials in regenerative medicine remains constrained by a convergence of manufacturing, reproducibility, interfacial, biological, regulatory, and economic barriers. While many of the aforementioned approaches are complex, low-throughput and not suitable for Good Manufacturing Practice (GMP) conditions, scalable production of Janus membranes, hydrogels, particles, microneedles and nanofibers and maintaining their asymmetric architecture and compartment-specific functions are considered fundamental bottlenecks (Omidian et al., 2025; Zhao et al., 2025). This is compounded by the lack of batch-to-batch reproducibility and the absence of standardization in fabrication, characterization and quality control procedures that are essential to guarantee the therapeutic performance and the identity of the material at the interfaces.

Unlike homogeneous biomaterials, Janus constructs require the preservation of structural asymmetry and interfacial integrity throughout fabrication, sterilization, storage, and scale-up (Mao H. J. et al., 2026). Mechanical loading, micromotion, and cyclic deformation can cause defects or delamination at the interface, especially in load-bearing applications, and traditional methods of sterilization, like ethylene oxide or gamma radiation, can also have differential effects on the constituent phases and on the functional asymmetry of the construct (Mao H. J. et al., 2026). These challenges are closely linked to the need for coordinated degradation across separate compartments where the differences in the material composition and degradation rates can continue to degrade the original architecture, weaken mechanical integrity, or produce degradation products that can cause a negative inflammatory response (Del Gaudio et al., 2026). Moreover, the multidimensional nature of Janus architectures, including unilateral adhesion, directional mechanical properties, gradient degradation, and compartment-specific drug release, is not adequately captured by conventional biomaterial testing methods, highlighting the need for standardized face-specific evaluation frameworks and clinically relevant performance metrics (Zhang J. Y. et al., 2025). From a biological perspective, long-term biocompatibility, biodegradation, immune responses, bioaccumulation, and the biological consequences of surface and structural anisotropy remain insufficiently understood, particularly for nanoscale Janus systems (Del Gaudio et al., 2026). Fundamental knowledge gaps concerning cell–material interactions, biofluid effects, adaptive tissue conformability, and the mechanisms governing asymmetric biological responses further limit rational optimization and reliable prediction of in vivo performance (Wong and Jang, 2025).

Regulatory translation presents an additional challenge because Janus platforms may simultaneously integrate structural, pharmaceutical, biological, and nanomaterial components, creating uncertainty regarding product classification, testing requirements, and harmonized regulatory pathways across jurisdictions (Qian et al., 2023). It is more complicated when creating patient-specific or adaptive Janus constructs, as manufacturing parameters, sterilization methods, and quality controls may differ among individual patients (Zhuo et al., 2024). Moreover, most evidence currently available is from in vitro studies or from relatively simple animal models, which may not adequately replicate the complex and dynamic microenvironments found in human tissue repair, and thus may not capture the predictive value of the outcomes of preclinical studies (Duan et al., 2021). Lastly, asymmetric architectures that are produced in a multistep process, require special equipment, quality control, and have limited production yields can significantly drive up manufacturing costs and pose questions about their cost-effectiveness and commercial scalability (Hrapović et al., 2026). These interconnected barriers indicate that successful clinical translation will require more than demonstrating superior regenerative efficacy. It will depend on the development of scalable and reproducible manufacturing platforms, robust strategies for preserving interfacial integrity and synchronized degradation, standardized dual-face characterization methods, comprehensive long-term safety assessment, human-relevant preclinical models, clearly defined regulatory pathways, and economically viable production strategies capable of accommodating the intrinsic complexity of Janus biomaterials.

6 Conclusion and future perspectives

Janus biomaterials are emerging as a distinctive class of next-generation regenerative platforms that move beyond the limitations of conventional homogeneous biomaterials toward spatiotemporally programmed and multifunctional systems. By integrating complementary biological, physicochemical, and therapeutic functions within a single asymmetric architecture, these platforms can more closely recapitulate the heterogeneous nature of native tissue microenvironments while coordinating key regenerative processes, including infection control, inflammation, angiogenesis, stem cell fate, and tissue remodeling. The diverse architectures reviewed here, ranging from electrospun nanofibers and asymmetric nanoparticles to multilayer membranes, biphasic hydrogels, and 3D/4D-bioprinted constructs, illustrate a progressive shift from passive structural support toward precision bioinstructive engineering. Importantly, the regenerative potential of Janus systems extends beyond structural asymmetry. Their spatially defined physicochemical cues have been shown to positively regulate cellular metabolism, immune responses and mechanobiological signaling, which suggests a new mechanistic dimension for Janus-mediated regeneration, namely, metabolic reprogramming. At the same time, the integration of ultrasound-, magnetic-, and piezoelectric-responsive components, together with advanced multilayer and personalized 3D/4D-printed architectures, is enabling on-demand therapeutic delivery, dynamic tissue modulation, and increasingly sophisticated sensing–feedback–actuation functions. These advances suggest a transition from multifunctional scaffolds toward adaptive platforms capable of responding dynamically to changes in the tissue microenvironment. While significant progress is being made, these achievements have been limited by the challenges of manufacturing at scale, manufacturing reproducibility, long-term structural and functional stability, characterization standardization, biosafety, and strict preclinical and clinical validation. Such barriers will need to be overcome through an integrated approach involving materials science, bioengineering, regenerative medicine, manufacturing, and regulatory science. In the future, Janus biomaterials can be combined with AI, personalized 3D/4D bioprinting, organ-on-chip models and smart biosensing technologies to allow for increasingly precise control of spatial and temporal therapeutic functions. Ultimately, future Janus platforms may evolve into intelligent bioinstructive interfaces that sense, interpret, and dynamically regulate the tissue microenvironment rather than merely supporting tissue repair. This paradigm shift positions Janus biomaterials as a compelling Frontier in precision regenerative medicine and a promising route toward clinically translatable, adaptive biomaterial therapies.

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Supplementary material

The Supplementary Material for this article can be found online at: https://www.frontiersin.org/articles/10.3389/frsfm.2026.1955040/full#supplementary-material

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Footnotes

Edited by: Sugam Kumar, Bhabha Atomic Research Centre (BARC), India

Reviewed by: Babak Mikaeeli Kangarshahi, Royan Institute, Iran

Mahsa Sedighi, Shahid Beheshti University, Iran