Smart hydrogel-based anticancer strategies for postoperative osteosarcoma management

1 Introduction

Osteosarcoma (OS) is a fast-growing malignant bone cancer that develops within bone and other musculoskeletal tissues (Marina et al., 2004; Wang X. et al., 2020). OS cells resemble premature bone-forming cells but produce mechanically weak bone; and it remains the most common primary malignant bone tumor (Guillon et al., 2011). Despite advances in multimodal treatment, OS remains a highly aggressive malignancy with a strong propensity for pulmonary metastasis, which is the leading cause of disease-related mortality. While patients with localized disease achieve 5-year survival rates of 60%–75%, outcomes decline sharply to 20%–30% once metastatic spread occurs (Jaffe et al., 2013; Lu et al., 2020). Current management relies on neoadjuvant chemotherapy, surgical resection and postoperative chemotherapy to control micro-metastatic disease and reduce recurrence risk (Carina et al., 2019). Standard regimens based on doxorubicin, cisplatin, methotrexate and ifosfamide have improved survival in localized disease; however, their clinical benefit is frequently limited by systemic toxicity, multidrug resistance and heterogeneous therapeutic responses (Zhang et al., 2018b; Liu et al., 2023; Wang S.-Y. et al., 2020). Radiotherapy has limited effectiveness in OS relying on emerging clinical advances (Machak et al., 2003; Shanmugavadivu et al., 2024). Following surgical resection, the affected bone region is left mechanically unstable, increasing fracture susceptibility and creating critical-sized defects that cannot heal spontaneously (Zhao et al., 2020). Conventional metallic implants provide immediate structural support but remain bioinert and may suffer from poor osteointegration, stress shielding or chronic inflammatory complications. In addition, residual malignant cells can persist after surgery, increasing the risk of local recurrence or distant metastasis (Zhang et al., 2019). Therefore, the development of advanced biomaterials that can effectively eliminate residual tumor cells, reduce systemic toxicity and simultaneously facilitate regeneration of critical-sized bone defects post-surgery is of paramount importance (Ma et al., 2016).

Hydrogels have emerged as promising candidates for this purpose owing to their high-water content, biocompatibility, tunable mechanics and extracellular matrix (ECM) mimetic architecture. Unlike rigid implants, hydrogels can conform to irregular resection cavities and act as localized depots for sustained delivery of chemotherapeutics, bioactive ions, proteins or immunomodulators while supporting cell infiltration and tissue repair (Cui et al., 2019; Han and Wang, 2022). Under normal physiological conditions, bone homeostasis is maintained through a balanced interplay between osteoblast-mediated bone formation and osteoclast-driven bone resorption. However, in OS, this balance becomes disrupted due to uncontrolled tumor growth, altered osteoclast activity and progressive bone degradation, ultimately leading to severe bone destruction and impaired regeneration. To address these challenges, advanced hydrogel-based systems have emerged as promising therapeutic platforms for OS management. Moreover, the OS microenvironment is characterized by acidity, oxidative stress, enzymatic dysregulation and inflammatory signalling, providing opportunities for the development of stimuli-responsive smart hydrogels with on-demand therapeutic activation (Chen et al., 2021; Lui et al., 2019; Su et al., 2020). Such materials can undergo reversible or irreversible changes in their physical properties or chemical structure in response to external physical stimuli (e.g., light, electric or magnetic fields, ultrasound and mechanical forces), endogenous pathological cues (e.g., elevated reactive oxygen species (ROS), mildly acidic conditions, endogenous electrical fields, altered ion concentrations, secreted enzymes or distinct immune microenvironments), or combinations of these triggers (Chen et al., 2020). Various strategies, including drug-eluting, biomolecule-loaded, photo-responsive, pH-responsive, temperature-responsive, ROS-responsive, functionalized and cell-laden hydrogels, have been developed to provide localized and stimuli-responsive therapeutic delivery as shown in Figure 1. In addition to suppressing tumor progression, these multifunctional hydrogel systems also support bone regeneration and postoperative defect repair following tumor resection.

However, despite these advances, current hydrogel systems face several critical limitations that hinder their clinical translation. Most studies rely on subcutaneous tumor models, which fail to recapitulate the complex bone tumor microenvironment (TME) and post-resection conditions, thereby limiting translational relevance. Additionally, there remains a significant gap between material design and spatiotemporal biological response, as therapeutic release profiles are not synchronized with the sequential requirements of post tumor resection and subsequent bone regeneration. Another major challenge is the insufficient mechanical stability of hydrogels, particularly in bone which is a load-bearing tissue, where inadequate structural integrity compromises their ability to support bone repair. Furthermore, many systems exhibit functional imbalance, achieving either effective tumor suppression or osteogenesis, but rarely both simultaneously. The increasing complexity of multifunctional hydrogels also raises concerns regarding reproducibility, scalability and regulatory feasibility. These challenges underscore the need for next-generation smart hydrogel systems that combine enhanced mechanical robustness, precise spatiotemporal control and improved translational relevance. In this review, we focus on recent advances in smart hydrogel platforms for postoperative OS management, emphasizing their potential to integrate localized tumor therapy with functional bone regeneration while addressing current limitations in design and translational clinical applicability.

2 Review methodology

This review evaluates recent advances in smart hydrogel strategies used for managing postoperative OS management, focusing on localized tumor therapy, bone regeneration, preclinical evaluation and clinical application. A thorough literature search was conducted using PubMed, Scopus and Web of Science to find relevant studies published between 2015 and June 2026. The search terms included combinations of osteosarcoma, smart hydrogel, stimuli-responsive hydrogel, injectable hydrogel, drug delivery, bone regeneration, bioactive ions, 3D bioprinting, 4D bioprinting, cell-laden hydrogel, photothermal therapy, immunotherapy, ferroptosis and animal models. Priority was given to original research articles reporting experimental evidence on hydrogel-based therapeutic strategies, whereas selected review articles were used to provide scientific context and identify emerging research trends. Studies were included whether they explored hydrogel-based biomaterials for OS treatment, reported In-vitro or In-vivo experimental findings, evaluated therapeutic or regenerative outcomes, or described innovative biomaterial design strategies with potential for real-world application. The chosen studies were evaluated according to hydrogel composition, fabrication strategy, therapeutic mechanism, stimuli responsiveness, drug delivery characteristics, regenerative performance, preclinical validation, and translational feasibility. Instead of providing a descriptive overview, this review compared the benefits and drawbacks of different hydrogel platforms, highlights currents challenges in translation, and outlines future directions for developing clinically applicable theranostic biomaterials for postoperative OS management.

3 Hydrogels for preventing OS recurrence

Hydrogel-based systems have emerged as a transformative strategy for OS management by addressing two critical and interrelated clinical challenges: postoperative tumor recurrence and large bone defect regeneration (Tharakan et al., 2023). Unlike systemic chemotherapy, which is limited by rapid clearance, poor tumor accumulation and off-target toxicity, hydrogel systems enable localized, sustained and stimuli-responsive drug delivery at the post-operative site. This is particularly beneficial in OS, where residual tumor cells in the poorly vascularized bone microenvironment are not effectively targeted by systemic treatments (Tian et al., 2022). Early drug-eluting hydrogels, including PLK1 shRNA/doxorubicin-loaded thermosensitive PLGA–PEG–PLGA and CPP-modified chitosan gene–chemotherapy systems, enhanced tumor suppression through prolonged local retention and reduced systemic toxicity (Cao Z. et al., 2024). Building on these systems, ion-releasing hydrogels containing bioactive ions (e.g., Mg²⁺, Sr²⁺ and Cu²⁺) offer dual functionality by promoting osteogenesis while exerting intrinsic antitumor effects through ROS generation, angiogenesis modulation and TMEregulation (Liu C. et al., 2024; Wu J. et al., 2025). In parallel, advanced platforms integrating gene delivery and immunomodulatory strategies, including miR-29b delivery and immune checkpoint blockade (e.g., PD-1/PD-L1 inhibition), further expand therapeutic potential by targeting tumor progression at molecular and immune levels (Freeman et al., 2023; Liu J. et al., 2021). More recently, theragenerative hydrogels have emerged as next-generation platforms integrating tumor eradication with bone regeneration. They provide spatiotemporal control, enabling early tumor ablation through chemotherapeutic, ion-mediated or external stimuli-responsive approaches, followed by sustained osteogenic repair. By overcoming limitations of intravenous therapy such as systemic toxicity, poor local bioavailability and inability to repair postoperative defects these multifunctional systems show strong promise for improving postoperative OS management, reducing recurrence and restoring bone function (Si et al., 2022; Dong Y. et al., 2025). With the rapid evolution of hydrogel platforms from passive drug carriers to multifunctional therapeutic systems, recent studies have proposed functional and mechanism-oriented classifications to better reflect their roles in OS management. These categorizations are primarily based on therapeutic modality, biological function and microenvironmental responsiveness, rather than solely on material composition.

3.1 Current clinical standard and unmet needs

Despite advances in multimodal therapy, postoperative management remains the greatest challenge in OS treatment. The current standard of care combines neoadjuvant chemotherapy, wide surgical resection, and adjuvant chemotherapy, most commonly the methotrexate–doxorubicin–cisplatin (MAP) regimen, resulting in improved survival for patients with localized disease (Isakoff et al., 2015; Bielack et al., 2002). Nevertheless, surgical excision frequently leaves critical-sized load-bearing bone defects and residual microscopic tumor cells that increase the risk of local recurrence, while pulmonary metastasis remains one of the major cause of OS related mortality (Albergo et al., 2017). However, tumor excision frequently results in critical-sized load-bearing bone defects while residual microscopic remains at the surgical margin predisposes patients to local recurrence. In addition, pulmonary metastasis continues to be the leading cause of OS related mortality, underscoring the limitations of local treatment alone (Yanhua et al., 2016). The hydrogel systems in this review represent a wide range of treatment strategies, including drug-loaded, ion-releasing, natural product-based, multifunctional, and cell based formulations. These platforms have been created to tackle specific challenges in postoperative OS care, such as local tumor control, immune response, bone regeneration, and tissue reconstruction that mimics natural conditions. While promising results have been achieved, most research is still in the early preclinical phase and depends on experimental models that do not accurately reflect post surgery, metastatic, or load bearing clinical situations. As a result this review evaluates hydrogel platforms based on their antitumor and osteogenic performance and their potential for real clinical use. This includes considerations for manufacturing scalability, integration into current clinical practices, regulatory issues and long-term safety (Qian et al., 2025).

3.2 Drug eluting hydrogels

Drug-eluting hydrogels play an important role in OS management by allowing localized and sustained delivery of therapeutic agents. This helps improve tumor control while reducing systemic side effects. In particular, injectable hydrogels can easily fill irregular post-surgical defects, ensuring better drug retention at the target site and enhancing treatment effectiveness (Hyun et al., 2018; Sun et al., 2020). These hydrogels can be further categorized based on the type of therapeutic agents they deliver, broadly into synthetic drugs and natural compounds. Synthetic chemotherapeutics such as doxorubicin and cisplatin offer potent anticancer activity; however, their clinical use is often limited by systemic toxicity as observed in conventional treatment approaches (Yoon et al., 2025). In contrast, natural compounds such as resveratrol and curcumin exhibit improved biocompatibility and offer additional benefits, including antioxidant activity and modulation of the TME, as reported in recent studies (Wei et al., 2021). Notably, these hydrogel systems are considered “smart” due to their ability to provide localized, controlled and often stimuli-responsive release of therapeutic agents within the TME. In this context, it is useful to consider these two categories separately. Overall, this classification points toward an increasing preference for drug-eluting hydrogels to balance efficacy and safety in OS management. Evaluating these differences helps guide the design of more effective and well-balanced hydrogel-based therapeutic systems.

3.2.1 Synthetic drugs

Synthetic drug-loaded hydrogels represent the earliest biomaterial platforms investigated for postoperative OS management, demonstrating localized chemotherapy to suppress residual tumor cells while minimizing systemic toxicity. By maintaining therapeutic drug concentrations within the resection cavity, these systems established the basis for local postoperative treatment and illustrated the advantages of hydrogel-mediated delivery over conventional systemic administration (Onaciu et al., 2019). A recent study reported galactose-based hydrogels functionalized with Imatinib, with or without nanohydroxyapatite, for localized OS therapy. Nanohydroxyapatite enhanced surface roughness and cell adhesion, while the hydrogel enabled controlled release. The Imatinib-loaded hydrogels showed concentration-dependent cytotoxicity and greater efficacy than free drug, supporting their potential for localized chemotherapy with reduced systemic toxicity (Sobierajska et al., 2023). Earlier systems primarily focused on sustained chemotherapy release. Galactose-based imatinib hydrogels and visible light-cured glycol chitosan platforms co-loaded with doxorubicin and cisplatin demonstrated that matrix-mediated retention can improve antitumor efficacy relative to free drug administration while reducing systemic toxicity (Chen et al., 2022; Yoon et al., 2019). Recent advances in injectable smart hydrogels highlight their potential as multifunctional platforms for localized OS therapy by integrating controlled drug delivery with adjunct regenerative or stimuli-responsive functions. A sodium alginate hydrogel incorporating Ti₃C₂T_x nanosheets, doxorubicin and icariin combined chemotherapy with near-infrared (NIR) photothermal therapy, achieving sustained release, efficient tumor ablation, reduced systemic toxicity and preservation of osteogenesis through mitigation of doxorubicin-induced impairment (Fu et al., 2025).

Similarly, pH responsive hydrogels take advantage of the acidic TME to release drugs selectively. In contrast, thermosensitive platforms blend chemotherapy with immunotherapy or photothermal therapy to slow tumor growth while promoting osteogenesis (Zhu et al., 2023; Yang et al., 2020; Li K. et al., 2022).

Similarly, a thermosensitive photothermal hydrogel containing ZnO microspheres and polydopamine provided sustained Zn²⁺ release with mild NIR-triggered heating, promoting osteogenic differentiation and improving in vivo bone regeneration (Ge et al., 2023). In parallel, magnetically responsive hydrogels and magnetic mesoporous bioactive glass scaffolds have emerged as promising platforms for combined tumor ablation and skeletal repair. Owing to the superior tissue penetration and non-invasive controllability of alternating magnetic fields, magnetothermal systems may be particularly advantageous for deep-seated bone lesions (Wei et al., 2022; Wu et al., 2011). Extending the scope of magnetic-responsive platforms, magnetically actuated microrobots fabricated from biodegradable hydrogels have recently emerged as precision systems for targeted OS therapy. Guided by external magnetic fields, these microrobots enable spatially controlled navigation and sustained co-delivery of anlotinib and MET inhibitor SCR1481B1 to overcome therapeutic resistance. In vitro, the combination produced pronounced synergistic cytotoxicity, markedly reducing cell viability and colony formation in both 2D and 3D tumor models, while unloaded carriers remained biocompatible. Their uniform size (∼150 μm) and controllable motility (∼3.5 μm/s) further confirmed their efficient directional movement. Collectively, this strategy highlights the translational promise of magnetically guided hydrogel microrobots for localized combination therapy and precision drug delivery in OS (Wang H. et al., 2024).

Despite these advances, convincing evidence that stimulus-responsive hydrogels can simultaneously achieve durable tumor control and functional bone regeneration under clinically relevant postoperative conditions remains limited. Future studies should therefore prioritize validation in orthotopic and post-resection models to determine whether their adaptive properties translate into meaningful therapeutic benefits beyond proof-of-concept demonstrations. As a result, achieving a balance between eliminating residual tumor cells and supporting tissue repair remains a key challenge with synthetic therapeutics. These concerns have driven a shift toward exploring natural bioactive compounds as alternative therapeutic agents. Natural compounds generally exhibit lower toxicity and possess multiple biological activities, such as anticancer, anti-inflammatory and regenerative effects. This makes them well-suited for incorporation into hydrogel systems designed for post-operative OS management. By offering a more balanced interaction with the biological environment, natural drug-based hydrogels provide a promising direction for developing safer and more effective theragenerative strategies.

3.2.2 Natural phytochemicals

Naturally derived anticancer compounds have gained considerable attention for OS management because of their multi-targeted biological activity and comparatively low toxicity (Liang et al., 2012). Nevertheless, many of these agents suffer from poor solubility, limited stability and rapid clearance, which restrict their therapeutic effectiveness. Smart hydrogel-based delivery systems offer a practical solution by acting as localized reservoirs that provide sustained and controllable release of natural drugs at the tumor site. Such platforms can improve drug bioavailability, reduce systemic exposure and create a favorable microenvironment for bone repair after tumor removal. Consequently, increasing research efforts are directed toward incorporating phytochemicals into smart hydrogels to achieve combined tumor suppression and bone regeneration, highlighting their potential for postoperative OS management (Sarkar and Bose, 2019). Recent studies demonstrate that the therapeutic outcome of phytochemical-loaded hydrogels depends on both the incorporated bioactive molecule and the material design. For example, recent study showed an acid-responsive hydrogel co-delivering gambogic acid and Ca²⁺ promoting mitochondrial apoptosis through calcium overload while preserving bone architecture and reducing pulmonary metastasis (Yang L. et al., 2025). In contrast, a shikonin-loaded nanocomposite hydrogel inhibited tumor progression through CDK1 suppression while enhancing immunotherapy by downregulating PD-L1 expression. Although both platforms use pH-responsive release, their distinct molecular mechanisms and regenerative outcomes emphasize that phytochemical selection should be tailored for specific therapeutic objectives rather than treating natural compounds as a uniform class (Chen X. Y. et al., 2025). Although both platforms use pH-responsive release, their distinct molecular mechanisms and regenerative outcomes emphasize that phytochemical selection should be tailored for specific therapeutic objectives rather than treating natural compounds as a uniform class (Dai et al., 2024). Similarly an injectable copper-coordinated Tremella fuciformis polysaccharide (TFP–Cu) hydrogel was developed as a cuproptosis-inducing platform for OS therapy. The system showed pH-responsive Cu²⁺ release, good injectability and selective cytotoxicity toward K7M2 cells by triggering cell-cycle arrest, apoptosis and mitochondrial dysfunction, while sparing normal cells. It also promoted M1 macrophage polarization and enhanced CD8⁺ T-cell responses, achieving ∼80% tumor inhibition in vivo. Additionally, the hydrogel upregulated osteogenic markers (ALP, OPN, OCN and Runx2), indicating its potential to support bone regeneration (Xie et al., 2024). Despite the promising therapeutic potential of natural drug-loaded hydrogels, several limitations still need to be addressed for effective OS management. Many phytochemicals exhibit variability in loading efficiency and stability within hydrogel matrices, which can influence release profiles and therapeutic consistency. In addition, achieving precise control over drug release kinetics remains challenging, particularly in complex TME where pH, enzymes and degradation behavior can vary significantly. Some systems also face limitations in achieving sufficient drug concentrations at deeper tumor sites, especially within dense bone tissues. Furthermore, while these hydrogels improve localized delivery, their standalone use may not fully address the need for simultaneous mechanical support and long-term bone regeneration in post-resection defects. To overcome these challenges, recent efforts have increasingly focused on multifunctional composite hydrogel systems that integrate drug delivery with structural reinforcement and bioactive components. Such approaches aim to enhance therapeutic efficacy while simultaneously supporting bone repair, providing a more comprehensive strategy for postoperative OS treatment.

Despite their promise, natural drug-loaded hydrogels face challenges in OS management, including variable drug loading, limited stability and inconsistent release in heterogeneous microenvironments. Their penetration in dense bone tissue and ability to provide sustained mechanical support and long-term regeneration also remain limited. To address this, recent strategies focus on multifunctional composite hydrogels that integrate drug delivery with structural and bioactive features. However, many systems remain preclinical, prioritizing tumor suppression over regeneration and raising concerns about safety, scalability and reproducibility. Future smart hydrogels should evolve into adaptive, patient-specific platforms capable of responding to dynamic post-operative cues while ensuring clinical feasibility and long-term performance. Key studies on drug-eluting smart hydrogels for OS therapy are summarized in Table 1.

TABLE 1. Therapeutic drug-releasing smart hydrogels for osteosarcoma management.

3.3 Micro/nanogel therapeutic hydrogels

Microgels and nanogels are three-dimensional, crosslinked polymer networks with dimensions in the micro to nanoscale that possess high water content, large surface area and tunable physicochemical properties (Sutradhar et al., 2025). Compared with bulk hydrogels, micro/nanogels offer superior injectability, enhanced tissue penetration and more precise control over drug loading and release behavior. Their small size and adaptable surface chemistry enable efficient encapsulation of chemotherapeutics, phytochemicals, nucleic acids and therapeutic ions, making them attractive carriers for localized OS therapy (Xuan et al., 2024). At present, micro/nanogels are frequently engineered to respond to defined internal or external stimuli, enabling spatiotemporally controlled drug release at tumor sites while reducing systemic exposure. Among these strategies, pH responsive micro/nanogels are especially promising for OS therapy (Miyata, 2026). These systems utilize the mildly acidic TME to trigger drug release through changes in polymer ionization, network swelling or cleavage of acid-sensitive bonds. Variations in pH alter polymer charge and intermolecular interactions, weakening forces that retain drugs within the hydrogel matrix and promoting release specifically at tumor sites. This targeted behavior is particularly beneficial in OS, where the local TME is acidic in nature, allowing controlled drug delivery with enhanced efficacy and no effects on non-targeted organs.

Collagen hydrolysate is a zwitterionic biomolecule containing pH-responsive groups such as hydroxyl and carboxyl moieties, enabling the formation of composite micro/nanogels through electrostatic interactions with other polymers. In addition to these interactions, drug release can be regulated by pH sensitive Schiff base linkages. Under physiological conditions, amine groups in gelatin react with aldehyde-containing polysaccharides to form stable imine bonds within the hydrogel network. In acidic TME, these bonds become unstable, leading to network breakdown and controlled release of encapsulated drugs, thereby enhancing targeted delivery (Du et al., 2025).

In line with this strategy, Nisha et al. developed a bio/nanocomposite hydrogel using oxidized catalpa gum, gelatin and Fe₃O₄ nanoparticles for co-delivery of doxorubicin hydrochloride and gentamicin sulfate. The network was formed via Schiff base crosslinking between the oxidized polysaccharide and gelatin. The presence of pH-sensitive imine bonds and ionizable groups enabled faster drug release under acidic conditions, driven by electrostatic repulsion between protonated carboxyl groups and doxorubicin. This system shows strong potential for localized, pH-responsive OS therapy (Rana and Sharma, 2024). Collagen-based materials are susceptible to enzymatic degradation by collagenase in bone tissue, enabling gradual matrix breakdown and sustained drug release. This property allows collagen-derived micro/nanogels to function as injectable depots for continuous delivery at defect sites, supporting bone repair Representative examples include dexamethasone-loaded gelatin nanoparticles that promoted prolonged drug release and enhanced expression of osteogenic markers, and collagen peptide–chitosan nanogels that improved doxorubicin-mediated apoptosis compared with the free drug (Qi et al., 2018; Anandhakumar et al., 2017).

Recent developments have further integrated multiple biological functions into nanogel platforms. Selenide-functionalized gelatin nanogels combine dual pH and glutathione-responsive release with reduced toxicity towards normal cells while maintaining effective tumour suppression (Das et al., 2024). In parallel, biomimetic nanogels and self-degradable hyaluronic acid nanogels have extended this concept by enhancing tumor targeting and tissue penetration through cancer cell membrane camouflage or enzyme-mediated ECM remodelling, resulting in improved intratumoral drug accumulation and therapeutic efficacy (Liu X. L. et al., 2021). In a research study Wang et al. developed a doxorubicin-loaded cancer cell–mimicking nanogel with enhanced tumor-targeting ability. In a 4T1 xenograft model, tumor fluorescence was ∼1.47-fold higher than non-mimetic nanogels at 12 h, indicating improved accumulation. The system achieved ∼70% tumor inhibition after 14 days, outperforming free doxorubicin and highlighting its potential for targeted anticancer therapy (Wang Y. et al., 2024). A hyaluronic acid–based self-degradable nanogel was designed for systemic delivery of anticancer proteins via an acid-triggered cascade mechanism. In acidic tumor conditions, the nanogel swelled and partially degraded, releasing hyaluronidase to break down the ECM and enhance tumor penetration, followed by intracellular release of DNase I to induce cell death. It showed higher tumor accumulation than free DNase I and achieved ∼62% tumor inhibition with reduced Ki-67 expression and minimal toxicity in vivo, highlighting its potential for targeted protein delivery (Zhu et al., 2018). While these hydrogel systems offer clear advantages in terms of injectability, controlled release and improved tumor targeting, certain limitations still constrain their practical application in OS therapy (Sutradhar et al., 2025; Kim et al., 2025). Their inherently soft structure and small size limit their mechanical strength, making them less suitable for supporting load-bearing bone defects following tumor resection. In addition, maintaining sustained retention at the target site can be challenging due to diffusion-related losses and potential burst release (Bose et al., 2012).

Issues related to scalability, reproducibility and consistent performance under complex physiological conditions further complicate their translation (Langer and Peppas, 2003). Despite the advantages of these hydrogel systems in achieving precise drug delivery and enhanced tumor penetration, their limited mechanical strength, retention and standalone regenerative capacity restrict their effectiveness in OS treatment. To address these challenges, recent strategies have shifted toward hydrogel-loaded composite systems. This approach enables the combination of targeted delivery precision with enhanced structural stability and osteogenic support, thereby providing a more comprehensive platform for simultaneous tumor suppression and bone defect repair.

3.4 Hydrogel-loaded composites

To address the limitations of microgel and nanogel based systems, recent studies have tried to address the mechanical robustness of hydrogel system for load bearing and regenerative capacity. Incorporating bioactive nanoparticles, therapeutic ions, or other functional fillers into hydrogel matrices to enhance their structural stability while preserving localized and controlled drug release. These composite platforms combine localized tumor control with bone regeneration, offering an integrated approach to the management of postoperative osteosarcoma (Yang et al., 2021; Zhao et al., 2022; Kortam et al., 2024). Bioactive ion-containing composite hydrogels illustrate both combined mechanical and therapeutic functionality. Chitosan–polyacrylamide (CS/PAM) hydrogels are biocompatible and mechanically stable but lack inherent osteogenic activity. Incorporation of magnesium-based nanoparticles introduces this functionality, as Mg²⁺ promotes mineralization, osteogenesis and angiogenesis. A nanoparticle-reinforced system (5NP/CMP@PAM) demonstrated stable NIR-induced heating, induced strong apoptosis in 143B OS cells, and completely prevented tumor recurrence in vivo. Concurrently, sustained Mg²⁺ release enhanced MC3T3-E1 osteogenic activity and improved bone regeneration, with increased bone volume, BMD and BMP-2/VEGF expression. These findings highlight such nanocomposite hydrogels as effective platforms for combined tumor ablation and bone repair (Li C. et al., 2022). However, the therapeutic outcome still remains a translational challenge prior to its long-term safety of nanoparticle incorporation requires further investigation before clinical application. Among these, bioactive ion-based composites have demonstrated the therapeutic value of combining localized tumor therapy with skeletal repair. For example, a magnesium nanoparticle-reinforced chitosan–polyacrylamide hydrogel promoted NIR-mediated tumor ablation while sustained Mg²⁺ release enhanced angiogenesis, osteogenic differentiation, and bone regeneration, illustrating the dual role of therapeutic ions in postoperative treatment (Onaciu et al., 2019).

OS treatment is challenged by recurrence, drug resistance and bone defects, driving interest in multimodal strategies such as chemodynamic therapy (CDT). More recently, composite hydrogels have been engineered to integrate multiple therapeutic mechanisms within a single biomaterial. For example, GelMA composites incorporating nHA/FePS₃ nanosheets combine photothermal, photodynamic, and chemodynamic therapies to target multiple oncogenic pathways along side osteogenic repair (Ye et al., 2025). Magnetically responsive and dual-responsive composite hydrogels offer an alternative to NIR-based platforms by enabling externally controlled therapeutic activation and stimuli-responsive drug release. Their ability to overcome the limited penetration of light makes them well suited for treating deep-seated bone tumors (Li Y. et al., 2022; Su et al., 2025; Sheng et al., 2022).

More recently, composite hydrogels have evolved from multifunctional therapeutic systems into platforms capable of providing spatially and temporally controlled therapeutic responses following tumor resection. A multifunctional hydrogel incorporating mineralized magnetic fibers was developed for OS therapy, demonstrating strong antitumor activity via NIR-induced photothermal effects that enabled localized tumor ablation and volume reduction in vivo. The system also exhibited antioxidative properties, protecting stem cells from oxidative stress and supporting their survival post-treatment. Additionally, calcium phosphate components promoted osteogenic differentiation, with increased expression of RUNX2, OPN and OCN, along with sustained mineralization. In vivo, the hydrogel enhanced bone formation and supported the development of mature, mineralized tissue. Overall, this platform highlights the potential of multifunctional hydrogels for simultaneous tumor ablation and bone regeneration (Byun et al., 2025). Three-dimensional (3D)-printed composite scaffolds have further expanded the horizons of hydrogel-based systems by enabling spatial and temporal separation of therapeutic and regenerative functions within a single construct. For example, an acid-responsive nano-hydroxyapatite/PLA scaffold incorporating a copper nanoparticle-loaded hydrogel delivered sequential chemodynamic therapy, induced cuproptosis, and subsequently released osteogenic ions to support bone regeneration (Xie et al., 2025) while a core–shell construct combining doxorubicin-loaded gelatin with a β-TCP/SrCuSi₄O₁₀ bioceramic shell integrated localized chemotherapy with therapeutic ion delivery to enhance bone repair (Zhang et al., 2023).

Despite their multifunctional advantages, hydrogel-loaded composite systems still face several challenges that may limit their clinical translation in OS management. The incorporation of multiple components, such as nanoparticles, therapeutic ions and drugs, can increase system complexity, making precise control over composition, reproducibility and scalability more difficult. In addition, achieving a balance between mechanical strength and degradation remains challenging, as excessive reinforcement may hinder biodegradability, while rapid degradation can compromise structural support (Li B. et al., 2025). Potential long-term biosafety concerns associated with inorganic additives and nanomaterials also require careful evaluation. Furthermore, the heterogeneity of the tumor–bone microenvironment can influence therapeutic performance, leading to variability in treatment outcomes (Tian et al., 2022). To address these limitations, current research is moving toward more precisely engineered and functionally tailored hydrogel systems, including surface-functionalized and cell-interactive platforms. These next-generation approaches aim to improve targeting specificity, biological integration and therapeutic efficiency, thereby advancing the development of more clinically viable solutions for postoperative OS management. An overview of hydrogel-loaded composite smart hydrogel approaches developed for OS treatment is provided in Table 2.

TABLE 2. Classification of composite hydrogels and their functional impact in osteosarcoma management.

3.5 Sustained ion release hydrogels

Building on advances in combination therapy, sustained therapeutic ion release has emerged as a powerful strategy for postoperative OS management, particularly within smart hydrogels. Unlike conventional drug-based systems, ion-mediated platforms use bioactive ions such as Zn²⁺, Sr²⁺, Mg²⁺, Ca²⁺, Cu²⁺, Fe²⁺/Fe³⁺ and Mn²⁺ to provide dual therapeutic action by suppressing tumor progression while promoting bone regeneration. As illustrated in Figure 2, sustained ion-releasing smart hydrogels can provide localized and prolonged therapeutic delivery within the OS microenvironment. The gradual release of bioactive ions contributes to multiple therapeutic functions, including tumor suppression, modulation of oxidative stress and immune responses, as well as stimulation of osteogenesis and tissue regeneration, thereby supporting simultaneous anticancer therapy and bone repair.

This unique capacity to simultaneously modulate cancer cells and restore the skeletal microenvironment has positioned sustained ion delivery as an increasingly important approach in OS therapy. Smart hydrogels provide a suitable platform for this approach by enabling controlled and sustained release of these ions at the target site. Recent work has shown that such systems can regulate key biological processes, including induction of apoptosis, generation of ROS, modulation of angiogenesis and promotion of osteogenic differentiation. Importantly, localized ion delivery minimizes systemic toxicity while maintaining therapeutic effectiveness. As research continues to expand, ion-releasing hydrogels are being increasingly recognized as a promising direction in OS management, offering a more integrated and biologically responsive alternative to conventional treatment strategies. (Bose et al., 2012; Hoppe et al., 2011; Wang et al., 2023; Qian et al., 2025). A comprehensive summary of recent advances in sustained ion release hydrogel for OS management, including their design strategies, therapeutic mechanisms and biological validation models is presented in Table 3.

TABLE 3. Therapeutic ion releasing hydrogels for osteosarcoma management.

Yao et al. developed a dual-ion-doped injectable organic–inorganic hydrogel designed for simultaneous tumor suppression and bone regeneration. The system combines a sericin-based dynamic network with selenium and magnesium-doped hydroxyapatite nanorods and polydopamine-coated CaO₂ nanospheres. It exhibits multimodal activity, where mild photothermal effects work synergistically with released selenite ions to induce tumor cell death. In parallel, sustained release of Ca²⁺, Mg²⁺ and PO₄ ^3- ions promotes osteogenic differentiation and supports bone repair. The hydrogel degradation is aligned with the healing process, enabling continuous bioactive support. Notably, the platform achieved complete tumor inhibition within 18 days and full bone regeneration over 12 weeks, highlighting its potential as a multifunctional theragenerative system for OS management (Yao J. et al., 2024). Recent studies further highlight the versatility of sustained ion-release systems in postoperative OS therapy. A magnesium oxide nanoparticle–reinforced chitosan hydrogel combined NIR-triggered photothermal ablation with sustained Mg²⁺ release, enabling effective tumor suppression while enhancing osteogenesis and bone repair (Li C. et al., 2022). Similarly, layered double hydroxide–modified bioactive glass scaffolds releasing Mg²⁺ and Zn²⁺ ions integrated photodynamic therapy with improved tumor inhibition and bone regeneration (Wang et al., 2026). Beyond direct cytotoxicity, ion-releasing systems can also modulate antitumor immunity. Injectable fibrin hydrogels containing ZIF-8 nanoparticles promoted localized chemo-immunotherapy, where Zn²⁺ release activated the STING pathway to reduce recurrence and metastasis. Likewise, alginate–gelatin hydrogels loaded with zinc-doped hydroxyapatite and 5-Fluorouracil combined sustained Zn²⁺ release with controlled chemotherapy for enhanced tumor killing (Elsayed et al., 2023). Copper-based hydrogels have also emerged as potent multifunctional platforms. An injectable Cu²⁺/rhein hydrogel combined sonodynamic therapy, ROS generation and cuproptosis for synergistic tumor inhibition (Zhang Y. et al., 2024). In parallel, MgO-based oxygen-generating hydrogels alleviated hypoxia while releasing Mg²⁺ to sequentially promote tumor suppression and bone regeneration after resection (Yu et al., 2026). In another study, a self-adaptive RPSH hydrogel was developed by incorporating RRx-001/ICG-loaded di-selenide nanoparticles into a PAAm/SA/HA dual-network matrix. The system initially modulates the post-operative inflammatory environment by promoting macrophage polarization, followed by dual-responsive anticancer activity through enhanced ROS/RNS generation, resulting in significant tumor inhibition. In addition, the hydrogel supports bone regeneration by maintaining osteogenic balance and promoting new bone formation. Sustained release of selenium ions prolongs therapeutic activity within the TME. The nanoparticles further exhibit redox-responsive behavior along with photothermal and photodynamic effects, enabling efficient tumor ablation under NIR irradiation. Overall, the integration of controlled ion release with multi-modal therapeutic mechanisms contributes to improved tumor suppression and regenerative outcomes (Lin et al., 2025).

Overall, these studies highlight the potential of ion-releasing hydrogels and scaffolds as multifunctional platforms for OS management. By combining sustained ion delivery with chemotherapy, phototherapy, immunomodulation and osteogenic cues, these systems can concurrently suppress tumor recurrence and promote bone regeneration. Such integrated strategies position ion-based biomaterials as promising candidates for next-generation therapies aimed at both OS management and post-resection bone repair. Although ion-releasing hydrogels offer clear advantages in OS management, several challenges still limit their full potential. Controlling ion dosage remains a critical concern, as excessive release can lead to toxicity and negatively affect surrounding healthy cells. In addition, maintaining consistent and predictable release behavior in complex biological environments is difficult, which can impact treatment reliability. The long-term effects of ion accumulation and their interactions with non-target tissues are also not yet fully understood. Moreover, while many ion-releasing systems have demonstrated efficacy against primary tumors, their ability to prevent or treat pulmonary metastasis—the leading cause of mortality in patients with OS—has not been adequately evaluated in preclinical studies and remains unexplored in clinical settings. Although these systems can support bone regeneration and exhibit anticancer activity, they lack the ability to fully reproduce the cellular complexity and dynamic interactions present in native bone tissue. These limitations suggest that further advancements are needed beyond ion-based, acellular platforms. As a result, recent research is increasingly shifting toward functionalized hydrogels to better replicate physiological conditions and enhance both regenerative and therapeutic outcomes.

3.6 Functionalized hydrogels

In recent years, hydrogel functionalization has gained significant momentum as an important direction in advanced OS research, because it allows the incorporation of multiple therapeutic functions within a single system. These engineered platforms integrate stimulus-responsive linkages, nanoparticles, bioactive agents and targeting moieties to improve therapeutic precision and efficacy. Functionalized hydrogels incorporate chemotherapeutics, ions and responsive elements within a single system to achieve controlled local delivery, enhanced tumor suppression and concurrent bone regeneration. Hydrogel-based systems also enhance local drug retention while reducing systemic exposure, thereby improving safety and treatment outcomes (Tharakan et al., 2023). Recent advances include oxidative stress-responsive platforms for targeted therapy (Salama et al., 2025; Zhu et al., 2025) and photothermally activated hydrogels that synergistically combine tumor ablation with tissue repair (Zhang et al., 2026; Phan et al., 2021). The expanding research in this field highlights the flexibility of functionalized hydrogels as dynamic and responsive biomaterials for OS therapy. Their ability to provide controlled spatial delivery, respond to environmental cues and integrate diverse treatment modalities positions them as a strong candidate for improving post-operative outcomes.

Functionalized smart hydrogels have shown strong potential for postoperative OS management by integrating localized therapy with bone regeneration. Li et al. developed a nanocomposite chitosan hydrogel containing polydopamine-modified magnesium nanoparticles that served as crosslinkers, photothermal agents and Mg²⁺ reservoirs. Under NIR irradiation, the system ablated 143B tumor cells, prevented recurrence and simultaneously promoted osteogenesis and bone repair (Li C. et al., 2022). Similarly, Chu et al. reported a magnesium-based hydrogel enabling sustained co-delivery of Mg²⁺, anti-PD-L1 antibody and vismodegib, which synergistically enhanced antitumor immunity, inhibited tumor growth and stimulated osteogenic differentiation (Chu et al., 2025). Injectable systems have further expanded translational relevance through minimally invasive delivery and conformity to irregular resection defects. A catechol-functionalized silk fibroin/sericin hydrogel exhibited injectability, self-healing, tissue adhesion and effective photothermal ablation of tumor cells while supporting pre-osteoblast proliferation (Chen S. et al., 2025). Likewise, CAP-treated alginate hydrogels sustaining reactive oxygen and nitrogen species release induced oxidative tumor killing and immunogenic cell death, thereby enhancing dendritic cell activation (Živanić et al., 2024). Similarly in order to address mechanical performance in load-bearing defects, reinforced scaffold-forming hydrogels such as HEMA/PNIPAM hybrids have been developed with enhanced strength, tunable swelling, pH-responsive doxorubicin release and osteogenic mineralization (Sreeja et al., 2021). These studies demonstrate that functionalization can be tailored to address distinct therapeutic challenges, including immune activation, mechanical reinforcement and stimulus-responsive drug delivery, rather than relying on a single therapeutic mechanism. Nevertheless, their therapeutic performance remains largely dependent on biomaterial-mediated biochemical cues and cannot fully recapitulate the cellular heterogeneity, immune interactions, and dynamic remodelling of the native OS microenvironment. Consequently, current research is increasingly shifting toward cell-laden hydrogels, where living cells are incorporated into engineered matrices to create more physiologically relevant platforms for investigating tumor biology, evaluating therapeutics, and supporting tissue regeneration.

3.7 Cell-laden hydrogels

Cell-laden hydrogels have emerged as a transformative strategy in OS management, enabling the integration of living cells within biomimetic matrices to simultaneously address tumor pathology enabling proper therapeutic screening and bone regeneration. For instance, Loessner et al., developed GelMA-based tumor models that demonstrated enhanced cell proliferation and drug resistance, highlighting the importance of matrix stiffness and architecture in regulating cancer cell behaviour (Weng et al., 2025). Similarly, Zhu et al., reported that bioprinted GelMA hydrogels encapsulating MG63 cells exhibited more clinically relevant responses to chemotherapeutics such as doxorubicin compared to 2D cultures. These findings are consistent with broader observations that 3D hydrogel systems better reproduce hypoxic gradients and diffusion limitations characteristic of solid tumors (Lin et al., 2022). In parallel, co-culture systems have gained increasing attention, where cancer cells are encapsulated alongside stromal or bone-related cells such as mesenchymal stem cells (BMSCs) or pre-osteoblasts. Further, Xu et al., demonstrated that co-culturing MG63 cells with BMSCs in hydrogel matrices enhanced tumor invasiveness and altered cytokine secretion, emphasizing the critical role of tumor–stroma interactions (Bassi et al., 2026). Cell-laden hydrogels have emerged as advanced biomimetic platforms that closely replicate the OS TME while supporting both therapeutic and regenerative applications. By incorporating cancer, stromal and stem cells within tunable matrices, these systems enable more realistic tumor modelling, drug screening and tissue regeneration studies. Notably, stromal cell inclusion has been shown to influence drug resistance and tumor progression, underscoring the importance of microenvironmental complexity. In this context, Mi et al. developed an integrated gradient biomechanical OS model using embedded bioprinting to better mimic the heterogeneous tumor environment. The system incorporated calcium-mediated mechanical gradients within fibrin-based bioinks and a self-healing ECM, enabling spatial variation in stiffness. This design successfully recreated key features of native tumors, including enhanced stemness, proliferation, migration and characteristic nest-like structures. Overall, such gradient cell-laden hydrogels provide a more physiologically relevant platform for studying tumor behavior, drug response and metastasis, offering clear advantages over conventional models (Mi et al., 2025). Recent advances in cell-laden hydrogels have focused on bioprintable multicomponent systems that better replicate the structural and dynamic features of the OS microenvironment. Jaiswal et al. developed a dual-extrusion 3D bioprinted model incorporating tumor and stromal cells within optimized bioinks, enabling precise spatial organization, high viability and stable constructs. Integration with a microfluidic bioreactor introduced perfusion and shear stress, resulting in greater tumor aggressiveness, enhanced cellular interactions and improved sensitivity to doxorubicin, cisplatin and sorafenib compared with static models (Jaiswal et al., 2025). Similarly, dECM-enriched hydrogels have improved biochemical fidelity by incorporating tumor-specific ECM signals.MG63-derived dECM integrated into GelMA–alginate–methylcellulose bioinks supported high printability, viability and spheroid formation, while inducing increased chemoresistance and upregulation of invasive markers relative to 2D cultures (Domingues et al., 2026). Complementing this, GelMA/HAMA-based 3D bioprinted models revealed multi-omics changes in metabolic, cell-cycle and epigenetic pathways, together with enhanced sensitivity to autophagy-targeted therapies (Lin et al., 2022). Collectively, cell-laden hydrogels bridge the gap between conventional in vitro assays and clinically relevant tumor models by more accurately recapitulating tumor architecture, cell–matrix interactions and therapeutic response, thereby strengthening their translational value for OS research and drug screening (Rijal and Li, 2017). Moreover, these systems offer opportunities to integrate therapeutic and regenerative functions, supporting both tumor suppression and bone repair. Recent advances incorporating mechanical gradients and dynamic culture conditions have further highlighted the importance of biomechanical and fluidic cues in regulating tumor behavior.

Building on these developments, 4D bioprinting has emerged as an extension of conventional bioprinting by enabling the fabrication of stimuli-responsive constructs that can change their shape or function over time (Figure 3). Most applications have been directed toward cartilage and vascular tissue engineering. For example, functionally modified silk methacrylate (SilMA)-based bioinks have been used to produce rapidly self-morphing hollow tubular structures through controlled swelling and visible-light crosslinking, achieving programmable structural transformations while preserving cell viability and mechanical stability. Likewise, photo-crosslinkable sodium alginate glycidyl methacrylate (SAGMA) bioinks exhibit reversible shape-morphing behaviour and structural adaptability in response to environmental stimuli, underscoring their potential as programmable 4D biomaterials. Although these systems have not yet been explored in osteosarcoma (OS) models, they offer a promising framework for designing smart hydrogels that can respond to pathological cues within the postoperative TME, such as acidic pH, thereby enabling self-fitting constructs, adaptation to irregular bone defects, and on-demand therapeutic release (Lv et al., 2025; Díaz-Payno et al., 2023; Kim et al., 2020; Sitarski et al., 2017).

Despite these promising advances, several translational challenges remain unresolved, including limited mechanical performance in load-bearing defects, inadequate evaluation of pulmonary metastasis, insufficient spatiotemporal control of therapeutic responses, manufacturing and scalability concerns, and the lack of standardized clinically relevant post-resection models. These limitations, together with the relative advantages and disadvantages of the various hydrogel platforms, are comparatively summarized in Table 4, highlighting the remaining barriers that must be addressed for the clinical translation of smart hydrogel systems in postoperative osteosarcoma management.

TABLE 4. Comparative analysis of hydrogel platforms for osteosarcoma management, highlighting their advantages, limitations, regenerative potential, and metastasis assessment.

4 Animal models in osteosarcoma: bridging preclinical research and clinical translation

Preclinical animal models play a pivotal role in OS research by enabling the translation of smart hydrogel-based strategies from controlled laboratory settings to clinically relevant therapeutic applications. Despite significant progress in the development of smart hydrogel systems for OS, successful clinical translation remains a major challenge. A critical step in this process is the use of appropriate animal models that can accurately predict therapeutic performance in humans. While small animal models, particularly murine systems, provide valuable insights into tumor biology and enable rapid evaluation of therapeutic efficacy, they often fail to replicate the complex anatomical, mechanical load bearing and immunological TME (Guijarro et al., 2014; Pu et al., 2023). In contrast, large animal models offer greater physiological and clinical relevance, allowing assessment under load-bearing conditions and more realistic surgical settings, but are limited by cost, scalability and experimental variability (Withrow and Wilkins, 2010; Yao M. et al., 2024). Therefore, a translational gap persists between early-stage preclinical findings and clinical application. Bridging this gap requires a strategic integration of small, intermediate and large animal models, enabling stepwise validation of hydrogel systems from mechanistic understanding to functional and clinically relevant performance. Such an approach is essential to advance smart hydrogel-based therapies toward safe and effective clinical use in OS management.

As illustrated in Figure 4, the preclinical evaluation of smart hydrogels for osteosarcoma (OS) encompasses both in vitro and in vivo studies, each addressing distinct aspects of therapeutic performance and translational potential. In vitro studies provide a controlled environment to investigate fundamental material and biological properties, including cytocompatibility, drug release kinetics, antitumor efficacy, osteogenic potential, and underlying cellular mechanisms. In contrast, in vivo studies evaluate hydrogel performance within a complex physiological milieu, enabling the assessment of postoperative bone defect repair, localized tumor suppression, biodegradation, host tissue interactions, and mechanical functionality. Together, these complementary approaches provide a comprehensive framework for translating smart hydrogel systems from bench to preclinical application.

4.1 Small animal models: mechanistic insights and limitations

Small animal models, particularly murine systems, are widely used for preclinical evaluation of hydrogel-based therapies in OS due to their controllability and rapid tumor establishment. Tumor induction is commonly achieved through xenografting, either subcutaneously using human OS cell lines such as MG63 or SaOS-2 for reproducibility, or orthotopically via intratibial or intrafemoral injection to better mimic tumor–bone interactions, osteolysis and metastasis. Although orthotopic models offer improved physiological relevance, both approaches rely on artificial tumor induction and therefore do not fully recapitulate natural disease progression (Zhang Q. et al., 2025). Within these models, hydrogel systems have demonstrated promising therapeutic outcomes. A comprehensive overview of preclinical animal models used in OS research, highlighting model type, tumor establishment methods and therapeutic evaluation outcomes is presented in Table 4.

Murine models have demonstrated effective tumor regression, metastasis suppression and bone regeneration, supporting their utility for early therapeutic validation (Yang Q. et al., 2025; Tharakan et al., 2023). However, their translational relevance remains limited due to differences in scale, immune deficiency and altered material behaviour, which can lead to exaggerated therapeutic outcomes (Kansara et al., 2014; Isakoff et al., 2015; Khanna and Hunter, 2005). Furthermore, mechanical limitations necessitate integration with rigid scaffolds, highlighting challenges in translating these systems to clinically relevant, load-bearing conditions (Yao J. et al., 2024; Peng et al., 2026; Zhang Y. et al., 2025; Xiao C. et al., 2024). Within this context, murine models have been widely employed in OS research to establish reproducible platforms for studying tumor implantation, progression and therapeutic response under controlled conditions. Tumor models are typically generated through subcutaneous (ectopic) or intratibial/intrafemoral (orthotopic) implantation of osteosarcoma cells, enabling evaluation of tumor growth dynamics, local invasion, and response to therapeutic interventions (Yao M. et al., 2024; Pu et al., 2023). Subcutaneous xenograft models are commonly used for rapid assessment of tumor regression and preliminary efficacy due to their ease of establishment and monitoring, whereas orthotopic models more closely recapitulate the native bone microenvironment, allowing investigation of tumor–bone interactions, osteolysis and metastatic potential (Khamarudin et al., 2024; Marques Da Costa et al., 2023). For example, an orthotopic OS model was established through a stepwise in vivo selection approach, wherein UMR-106 cells were initially implanted into the marrow cavity of Balb/C nude mice, followed by serial transplantation of tumor fragments into the marrow cavities of cyclosporine A–immunosuppressed SD rats. Through multiple rounds of in vivo selection and acclimatization, immune-tolerant osteosarcoma cell lines were generated, enabling the successful establishment of orthotopic tumors in SD rats with intact immune systems. Micro-CT imaging confirmed tumor-induced osteolysis and progressive bone destruction, closely mimicking clinical disease pathology. Importantly, this strategy was further translated to medium-sized animal models, wherein VX2 tumor fragments were implanted into the distal femur and radius of New Zealand white rabbits, resulting in consistent orthotopic tumor formation under load-bearing conditions. These rabbit models provide enhanced anatomical and biomechanical relevance compared to murine systems, enabling evaluation of tumor progression, bone destruction and therapeutic performance in a more clinically representative environment (Yao M. et al., 2024). In contrast, conventional small-animal models, particularly murine systems, often fail to fully recapitulate the clinical complexity of postoperative OS. Reproducing local tumor recurrence following intratibial resection and the spontaneous development of pulmonary metastasis remains challenging due to the limited anatomical dimensions and differences in biomechanical loading, thereby restricting their translational relevance for evaluating post-resection therapeutic strategies. As illustrated in Figure 5, preclinical OS animal models provide varying degrees of translational relevance for evaluating multifunctional smart hydrogels, which can enable localized therapeutic delivery, postoperative defect restoration and enhanced bone regeneration.

4.2 Intermediate animal models: translational bridge between murine and large animal models

Intermediate animal models, particularly rabbit systems, serve as an important translational bridge between murine studies and clinically relevant large animal models in OS research (Table 5). While murine models are essential for early validation, they fail to capture the anatomical scale, biomechanical loading and surgical complexity of human disease. In contrast, rat and rabbit models enable evaluation of biomaterial-based therapies under more physiologically relevant and mechanically demanding conditions. In rabbit models, OS is commonly established through orthotopic implantation of VX2 tumor fragments into long bones such as the femur or radius, resulting in reproducible tumor formation within the native bone microenvironment. These models effectively recapitulate key pathological hallmarks of osteosarcoma, including progressive osteolysis, cortical bone destruction, neoplastic calcification and pulmonary metastasis under load-bearing conditions. Consequently, rabbit systems provide enhanced relevance for investigating tumor–bone interactions, disease progression and therapeutic response compared with murine models (Yao M. et al., 2024). In a representative study, a spontaneous case of OS in a domestic rabbit (Oryctolagus cuniculus) underscores the pathological relevance of rabbit models in osteosarcoma research. The tumor originated in the tarsal joint region, involving the distal tibia and exhibited pulmonary micro metastases, reflecting a key clinical feature of disease progression. Histologically, the neoplasm comprised a heterogeneous population of ovoid to short spindle-shaped tumor cells interspersed with multinucleated giant cells, with prominent formation of irregular osteoid islands indicative of osteogenic activity. Immunohistochemical analysis revealed strong osteocalcin expression, confirming the osteoblastic origin of the tumor cells. Notably, a review of reported cases suggests that productive osteoblastic OS is the most prevalent bone tumor subtype in rabbits, frequently affecting craniofacial regions. Collectively, these findings highlight the capacity of rabbit models to recapitulate critical histopathological and metastatic features of OS, reinforcing their value in translational and preclinical research (Ishikawa et al., 2012). In intermediate animal systems, OS is commonly induced via intraosseous injection or orthotopic tumor implantation, followed by the creation of critical-sized bone defects to simulate post-resection conditions. These models enable simultaneous evaluation of tumor control and bone regeneration within a more physiologically relevant and load-bearing environment. Composite scaffolds incorporating bioactive ceramics or calcium phosphate phases have demonstrated enhanced osteointegration, vascularization and structural stability in rabbit long bone defects (Rezwan et al., 2006). In OS-specific studies, similar composite strategies integrating therapeutic functionality have shown effective tumor suppression alongside bone repair (Zhang Y. et al., 2025). Despite these advantages, intermediate models retain certain limitations. They do not fully replicate the genetic heterogeneity, metastatic behavior and immune complexity of human OS (Haney and Holstein, 2025) and tumor induction methods still bypass natural disease evolution. Practical challenges such as higher cost, surgical complexity and variability also limit widespread use. Notably, these models reveal a critical limitation of hydrogel systems; while structurally adequate in murine models, hydrogels often fail under increased mechanical demands, highlighting their insufficient load-bearing capacity (Table 6). This has driven a shift toward composite and reinforced systems, which better meet clinical requirements. Overall, rat and rabbit models function as key decision-making platforms in the translational pipeline, enabling selection of biomaterials that can withstand physiological, mechanical and surgical constraints before advancing to large animal studies and clinical application.

TABLE 5. Translational animal models for osteosarcoma therapeutics.

TABLE 6. Comparative overview of preclinical animal models for the evaluation of hydrogel-based OS therapeutics.

4.3 Large animal models: toward clinical translation and remaining gaps

Large animal models represent the final and most clinically relevant stage of preclinical OS research, offering a level of biological and anatomical fidelity not achievable in smaller animal models. Among these, spontaneous tumor in dogs is widely regarded as the most representative model, closely mirroring human disease in terms of tumor heterogeneity, genetic complexity, metastatic progression and therapeutic response. Unlike induced rodent models, canine OS arises naturally within the bone microenvironment, preserving critical interactions between tumor cells, immune components and bone remodelling processes (Fan et al., 2020). A key advantage of canine models is their compatibility with clinically relevant interventions, including limb-sparing surgery, implant placement and evaluation of adjuvant therapies. Biomaterial-based strategies, such as drug-loaded implants and bioactive scaffolds, have been assessed in canine patients to achieve localized tumor control while supporting bone regeneration (Gordon et al., 2009). In addition, these models have enabled evaluation of immunotherapeutic approaches, including immune checkpoint inhibitors and cancer vaccines, providing insights not accessible in immunodeficient rodent systems (Tawbi et al., 2017). Despite these strengths, the application of hydrogel-based systems in large animal models remains limited, highlighting a key translational gap. While hydrogels show strong performance in small animal studies, their clinical translation is constrained by insufficient mechanical strength, scale-up challenges and handling limitations. In load-bearing bones such as the femur or humerus, hydrogels alone cannot withstand physiological stresses and therefore require integration with rigid scaffolds or implants (Simpson et al., 2017). Consequently, most large animal studies prioritize composite systems over standalone hydrogels, underscoring a disconnect between early-stage material design and clinical applicability. Practical and ethical considerations, including cost, variability and limited standardization, further restrict the use of canine models. Alternative large animal systems, such as sheep and porcine bone defect models, provide advantages in terms of size and mechanical loading for evaluating implant performance.

However, they do not naturally develop OS, limiting their ability to capture tumor biology and immune interactions. Overall, large animal models reveal a critical translational bottleneck; while hydrogels are extensively optimized for multifunctionality in early-stage studies, their role in clinically relevant settings is often reduced to supportive components within composite systems. Bridging this gap will require the development of mechanically robust, scalable and surgically compatible hydrogel-based platforms, along with integrated multi-scale validation strategies aligned with clinical needs.

5 Integration with advanced technologies

Despite significant progress, the clinical translation of hydrogel-based therapies for osteosarcoma remains challenging. Most preclinical studies fail to bridge the gap between subcutaneous tumor models and post-resection models that more closely address the post-operative tumor recurrence challenge (Xiao et al., 2021; Liu G. et al., 2021; Dong H. et al., 2025). Furthermore, there remains a disconnect between therapeutic design and spatiotemporal biological response, where drug or ion release profiles are not precisely synchronized with tumor eradication and regeneration (Lai et al., 2026). Importantly, translational efficacy remains limited due to challenges in reproducibility, scalability and regulatory feasibility and metastasis to other organs (Wang et al., 2025). Addressing these limitations will require a transition toward next-generation smart hydrogels that are adaptive, multifunctional and clinically integrated. Rather than serving solely as passive depots, future hydrogels are expected to function as a multifunctional system capable of dynamically responding to pH, ROS, enzymes, hypoxia, inflammatory signals and mechanical changes within the postoperative microenvironment. Recent studies already exemplify this evolution. A pH responsive peptide hydrogel enabled localized drug release under acidic tumor conditions, while an aptamer-decorated DNA hydrogel fabricated by rolling circle amplification achieved receptor-specific targeting with combined chemotherapy and nucleic acid delivery (Zhu et al., 2023; Jin et al., 2022). Likewise, a gelatin–genipin hydrogel incorporating mineralized magnetic fibers combined NIR-triggered photothermal tumor ablation and osteogenic regeneration (Byun et al., 2025). Complementing these systems, an enzyme-responsive supramolecular hydrogel exploited alkaline phosphatase overexpression to trigger selective tumor-surface self-assembly and biomineralization-mediated cytotoxicity, thereby overcoming conventional multidrug resistance (Yang et al., 2023). Together, these examples highlight the shift from conventional carriers toward precision theragenerative biomaterials.

A major future driver of this field will be Artificial Intelligence (AI) and data-enabled biomaterials engineering. AI and machine learning can accelerate optimization of hydrogel composition, crosslink density, nanoparticle loading, degradation behaviour, mechanical performance and spatiotemporal release profiles by correlating formulation parameters with therapeutic outcomes. Predictive models may also support personalized treatment planning by integrating tumor phenotype, imaging signatures, chemoresistance patterns or metastatic risk, thereby reducing empirical trial-and-error development. Although still emerging, such approaches could substantially shorten the path from laboratory design to clinically optimized hydrogel systems. In parallel, image-guided and patient-specific fabrication strategies are likely to transform postoperative OS management. However, successful clinical translation will require robust use of machine learning and standardized datasets and closer integration of biomaterials research, computational modelling, and clinical validation. In parallel, image-guided fabrication using computed tomography (CT), magnetic resonance imaging (MRI), and optical imaging are expected to play an important role in improving anatomical conformity of customised hydrogel implants and bioprinted scaffolds by accurately defining tumor margins and post-resection defects (Isakoff et al., 2015; Dawson and Sharpe, 2006; Igrec and Fuchsjäger, 2021). This is particularly critical in OS, where incomplete resection or undetected residual cells can result in recurrence and poor clinical outcomes (Roessner et al., 2021). Recent advances have further enabled the development of multifunctional, image-guided nanoplatforms. For example, a biomimetic system incorporating Fe-MOF, polydopamine and erastin, coated with cancer cell membranes, has demonstrated effective targeted therapy (Liu Y.-J. et al., 2024).

In parallel, personalized hydrogel therapy is emerging as a promising strategy to design biomaterial similar to the OS TME and patient-specific clinical needs. Combined with 3D bioprinting, stimuli-responsive hydrogels enable localized therapeutic delivery and the fabrication of patient-specific constructs that fit to irregular post-resection bone defects. However, reproducible fabrication, sufficient mechanical stability, and long-term structural integrity still remain major challenges, particularly for load-bearing applications. Notably, the majority of recently reported hydrogel systems primarily focus on local tumor suppression and bone regeneration, whereas the evaluation of metastatic progression, particularly pulmonary metastasis, remains largely underexplored. Given that metastasis is the principal cause of mortality in patients with OS, future studies should prioritize the integration of advanced technologies and clinically relevant models to enable comprehensive assessment of both local therapeutic efficacy and metastatic outcomes (Han et al., 2025; Li Z. et al., 2025). In practice, these hydrogels often serve a dual role functioning as drug delivery systems while also acting as ECM-like scaffolds that support osteogenic differentiation and bone regeneration (Tian et al., 2022). Incorporation of nanoparticles, bioactive ions and natural compounds further enables multimodal therapy, although controlling interactions among components remains complex (Kortam et al., 2024). The addition of imaging functionality has further expanded hydrogel utility. By integrating contrast agents or fluorescent probes, hydrogels can be monitored using MRI, CT or optical imaging, allowing real-time tracking of localization and therapeutic progression particularly valuable in OS, where residual disease may drive recurrence. Nevertheless, long-term safety and agent accumulation require careful evaluation (Qian et al., 2025). Recent theranostic hydrogels integrating diagnostics with therapy exemplify this trend. Photothermal systems enable NIR-triggered tumor ablation while sustained release of bioactive cues supports bone repair; notably, copper-based nanoparticle hydrogels have shown simultaneous tumor destruction and osteogenesis (Wu F. et al., 2025). Although these platforms reflect a shift toward precision postoperative care, clinical translation remains limited by fabrication, complexity and scalability (Tharakan et al., 2023). As shown in Figure 6, the integration of AI and data-driven approaches offers new opportunities to optimize hydrogel design. Predictive models capable of correlating material composition with drug release and therapeutic outcomes may accelerate the development of next-generation systems. However, the reliability of such approaches depends heavily on the availability of robust experimental datasets. Overall, while personalized and image-guided hydrogels represent a promising direction in OS therapy, their successful clinical implementation will require continued efforts to balance multifunctionality with safety and scalability.

6 Conclusion & future perspectives

Smart hydrogels have evolved into a multifaceted platform for OS management, extending beyond conventional drug delivery toward integrated therapeutic systems. The diverse strategies discussed in this review including drug-eluting hydrogels, sustained ion-releasing hydrogels, micro/nanogel-based hydrogels, surface-functionalized hydrogels and cell-laden hydrogels highlight the capacity of these materials to achieve localized, controlled and stimuli-responsive delivery within the TME. Such approaches improve drug retention and therapeutic specificity while reducing systemic toxicity. In addition, bioactive ion incorporation and surface functionalization provide opportunities to modulate cellular responses, supporting both anticancer activity and tissue regeneration. Recent advances further demonstrate the potential of hydrogel-loaded composites and 3D/4D constructs to address the dual requirements of tumor eradication and bone defect repair. These systems offer enhanced structural support and spatiotemporal control over therapeutic release, making them more suitable for the functional demands of bone tissue. Similarly, cell-laden hydrogels have contributed to the development of more physiologically relevant models by recapitulating tumor–stromal interactions, angiogenesis and drug response. However, their integration into clinically applicable therapeutic platforms remains limited, indicating a gap between experimental innovation and translational utility. Despite these promising developments, several critical challenges remain. In the context of OS, clinical translation is constrained by the inherently low mechanical strength of hydrogels in load-bearing bone environments. In addition, their limited penetration within the dense tumor–bone microenvironment can result in heterogeneous drug distribution, while variability in degradation behavior may lead to inconsistent release kinetics. Most current systems primarily target localized tumors and often fail to adequately address metastatic progression, particularly to the lungs. Furthermore, incomplete understanding of hydrogel–immune system interactions, potential long-term toxicity of incorporated functional agents and difficulties in achieving reproducible large-scale fabrication present additional barriers. The widespread reliance on subcutaneous or low-load-bearing models further limits the predictive value of preclinical findings. Furthermore, few investigations have simultaneously assessed tumor eradication, prevention of metastasis, and functional bone regeneration within a single platform. The lack of standardized protocols for mechanical characterization, degradation assessment, and long-term biosafety evaluation further complicates cross-study comparisons and translational assessment. Additionally, hydrogel interactions with the immune microenvironment remain poorly understood, despite their potential influence on therapeutic efficacy and tissue regeneration. Addressing these gaps will require the development of multifunctional, mechanically robust, and clinically translatable hydrogel systems validated in physiologically relevant models and supported by scalable manufacturing strategies. Looking ahead, next-generation smart hydrogel systems are expected to integrate adaptive and programmable functionalities, supported by advances in AI/ML-driven material design and optimization. These approaches may enable more precise control over hydrogel properties and therapeutic performance. In parallel, the development of personalized hydrogel platforms tailored to patient-specific tumor characteristics, along with the incorporation of image-guided therapeutic strategies, holds significant promise for improving treatment precision and monitoring. In summary, smart hydrogels represent a rapidly advancing and conceptually robust approach for OS management, combining localized therapy, stimuli-responsive behavior and regenerative capability within a single platform. However, overcoming current biological, material and translational limitations will be essential to fully realize their clinical potential. Continued interdisciplinary efforts will be critical in bridging the gap between experimental innovation and effective clinical application in OS management.

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Footnotes

Edited by: Lorenzo Vannozzi, Sant’Anna School of Advanced Studies, Italy

Reviewed by: João C. Silva, University of Lisbon, Portugal

Guangfeng Li, Shanghaizhongye Hospital, China