Recent progress of cellulose-based ionogels in processing strategies, functional behavior and flexible applications

1 Introduction

Cellulose-based ionogels have attracted increasing attention in flexible electronics because they can serve as versatile functional materials for diverse sensing and actuation scenarios (Hopson et al., 2021). In these systems, cellulose plays a central role in regulating ionic-liquid confinement across multiple length scales by controlling ion distribution, mobility, and the continuity of transport pathways. Its hierarchical hydrogen-bonded structure also enables efficient stress dissipation, allowing the material to maintain mechanical robustness under large deformation without severely compromising ionic conductivity. In addition, the nanoscale architecture of cellulose promotes the formation of interconnected ion-transport channels and stabilizes ion–polymer and ion–ion interfaces through strong intermolecular interactions. Therefore, cellulose is not merely a green supporting scaffold; rather, it acts as an integral structural and functional component that participates in ionic-liquid confinement, stress dissipation, interfacial stabilization, and ion transport (Liu et al., 2026).

The dissolution of cellulose has been extensively investigated through both experimental and computational approaches to deepen the understanding of solvent–cellulose interactions, hydrogen-bond disruption, and structural transformation. Ionic liquids (ILs) and deep eutectic solvents (DES) have emerged as effective media for cellulose dissolution and network reconstruction, providing new opportunities to construct cellulose-based ionogels with tunable microstructures and functional properties (Li et al., 2018; Janesko, 2011).

After effective cellulose dissolution, network architecture can be established through various molecular interactions. These interactions guide the formation of continuous hierarchical fibrillar networks with tunable porosity, ionic-domain distribution, and pathway connectivity. Such engineered networks determine the structure–property relationships of cellulose-based ionogels by simultaneously regulating ion-transport continuity and stress dissipation across multiscale architectures. As a result, rational network design enables the development of multifunctional materials for wearable electronics, flexible sensors, actuators, and related soft devices (Liu et al., 2026; Lon et al., 2024; Taokaew, 2023; Kowalczuk et al., 2023).

Most existing reviews summarize cellulose-based ionogels mainly according to their isolated functions or properties. As a result, a disconnected understanding persists between molecular-level interactions, processing routes, and its performance. In contrast, this review provides a distinct perspective by explicitly connecting cellulose precursor, ionic media, with particular emphasis on dissolution-regeneration pathway, network architecture design, and functional role within a single continuous framework. This enables a clear understanding of how processing history governs structure formations and ultimately regulates performance such as mechanical robustness, electrochemical stability, dynamic adhesion and self-healing behavior in flexible electronics systems. Finally, the current challenges and future perspectives of cellulose-based ionogels are critically examined to guide their continued development for next-generation flexible applications.

2 Cellulose precursors and ionic media

Cellulose and ionic media are the two fundamental components for constructing cellulose-based ionogels. Cellulose provides the structural framework, whereas ionic media enable cellulose dissolution, network reconstruction, and functional ion transport. With the growing demand for sustainable and environmentally friendly flexible materials, biodegradable cellulose resources and ionic media have attracted increasing attention. Therefore, understanding the roles of these components is essential for the rational design, fabrication, and performance regulation of cellulose-based ionogels. Owing to their tunable physicochemical properties and strong solvation ability, ILs and DES represent promising ionic media for cellulose processing.

2.1 Cellulose precursor

Cellulose precursors derived from different sources, including wood pulp, cotton fibers, bacterial cellulose, and agricultural residues, vary significantly in purity, crystallinity, molecular weight, and fibrillar architecture. These intrinsic differences strongly influence the dissolution–gelation behavior and the final structure–property relationships of cellulose-based ionogels (Isik et al., 2014; El Seoud et al., 2019). For example, plant-derived pulp is widely available but often exhibits limited structural uniformity, cotton cellulose generally provides higher crystallinity and mechanical strength, whereas bacterial cellulose possesses an inherent nanofibrillar network. Therefore, precursor selection is a critical factor for balancing mechanical reinforcement and ionic transport in cellulose-based ionogels (El Seoud et al., 2019; Swatloski et al., 2002; Zhu et al., 2006; Ji et al., 2026).

In addition, cellulose nanofibers and cellulose nanocrystals are particularly attractive because of their high aspect ratio, high tensile strength, low density, and abundant surface hydroxyl groups. Even at low loadings, typically 1–10 wt%, these nanocellulose components can effectively enhance tensile strength, Young’s modulus, and fracture resistance (Lee et al., 2021; Ge et al., 2026; Takeno et al., 2022). In cellulose-based ionogels, the cellulose not only improves mechanical robustness but also helps maintain flexibility and ionic conductivity. These features are essential for long-term operation under bending, stretching, and other mechanical deformations, making cellulose-based ionogels promising multifunctional materials for flexible electronics and soft robotic systems (Takeno et al., 2022; Le Bideau et al., 2011).

2.2 ILs

ILs are organic salts composed entirely of cations and anions, typically with melting points below 100 °C (Nasirpour et al., 2020). They have attracted broad interest because their physicochemical properties can be tailored by varying cation–anion combinations. Their negligible volatility, non-flammability, high thermal stability, and strong solvation ability enable the dissolution of various biopolymers, including cellulose, chitosan, and chitin, which are generally difficult to dissolve in conventional solvents (Karuppasamy et al., 2020). It should be noted that several related terms have been used in previous studies, including confined ILs, ion gel, IL-gel, and ionogel (Wang Z. et al., 2020; Karimi and Badreh, 2011; Prasad and Bhatt, 2015; Zhu et al., 2019). In this Review, the term “cellulose-based ionogel” is used to describe gel systems in which cellulose forms the structural network and ILs are confined within the gel matrix. In such systems, ILs not only act as dissolution media but also contribute to ionic conductivity, electrochemical stability, and functional responsiveness. By adjusting the structure and content of ILs, key properties such as conductivity, viscoelasticity, thermal stability, and interfacial interactions can be regulated.

2.3 DES

DES are liquid mixtures that generally exhibit melting points below 100 °C. They are commonly formed by combining hydrogen-bond acceptors and hydrogen-bond donors. Typical DES systems include hydrated metal halides with quaternary ammonium salts, non-hydrated metal halides with quaternary ammonium salts, hydrogen-bond donors with quaternary ammonium salts, and metal halides with hydrogen-bond donors (Zhang et al., 2012). Because of their low volatility, low cost, biodegradability, and tunable physicochemical properties, DES have emerged as sustainable alternatives for cellulose processing. Among them, choline chloride-based systems combined with urea, glycerol, or organic acids are the most commonly used DES for cellulose dissolution and modification (Zhang et al., 2012; Abbott et al., 2003; Cichowska-Kopczyńska et al., 2023). Although their cellulose dissolution ability is generally lower than that of many ILs, their environmental compatibility and design flexibility make them attractive candidates for developing greener cellulose-based ionogel systems.

3 Dissolution and regeneration mechanism

Cellulose is insoluble in water and most conventional organic solvents because of its high crystallinity and dense intra- and intermolecular hydrogen-bonding. Therefore, efficient solvent systems are required to disrupt these interactions and enable cellulose dissolution (Swatloski et al., 2002). Historically, several solvent systems have been developed for cellulose processing, among which the viscose process is one of the most established methods (El Seoud et al., 2019). However, this process involves chemical derivatization of cellulose and raises serious environmental and health concerns (Isik et al., 2014). To overcome these limitations, non-derivatizing solvent systems, including N, N-dimethylacetamide/lithium chloride, ammonium fluoride/dimethyl sulfoxide, and N-methylmorpholine-N-oxide, were developed. These solvents can disrupt cellulose hydrogen bonding while preserving the covalent backbone of cellulose. Among them, N-methylmorpholine-N-oxide has been used at the industrial scale because of its relatively low toxicity, biodegradability, and high recovery rate. Nevertheless, it still suffers from oxidative side reactions, high dissolution temperatures, and thermal instability (Acharya et al., 2021). In recent years, ILs and DES have been widely investigated as promising cellulose solvents. These media exhibit low vapor pressure, good recyclability, strong dissolution ability, and high thermal stability, and can dissolve cellulose at relatively high concentrations, typically up to 15–20 wt% (Rosenau et al., 2005). At the molecular level, both ILs and DES disrupt the native hydrogen-bonding network of cellulose, promote chain separation, and transform cellulose into a molecularly dispersed or highly swollen state (Isik et al., 2014). During regeneration, usually induced by an antisolvent, solvent–cellulose interactions are gradually weakened, allowing cellulose chains to reassociate through inter- and intramolecular hydrogen bonding. However, because ILs and DES differ in polarity, coordinating ability, viscosity, and regeneration kinetics, they strongly influence the pathway of cellulose chain reassembly. Rapid regeneration tends to generate compact and highly crystalline domains, whereas slower regeneration generally favors more porous and fibrillar networks. Therefore, dissolution and regeneration are not merely processing steps but key determinants of the final architecture design and functional performance of cellulose-based ionogels.

3.1 IL-based systems

ILs are composed of organic cations and organic or inorganic anions. Typical cellulose-dissolving ILs contain anions such as OAc⁻, HCOO⁻, Cl⁻ and phosphonate-based species, together with cations such as imidazolium or pyridinium derivatives (Isogai and Atalla, 1998). Extensive experimental and computational studies have shown that both anions and cations participate in cellulose dissolution, although their roles are different (Bentivoglio et al., 2006; Mohd et al., 2017). In general, anions directly interact with cellulose hydroxyl groups and disrupt the native hydrogen-bonding network, whereas cations stabilize the dissolved cellulose chains and modulate solvent structure (Potthast et al., 2003). The dissolution behavior of cellulose in ILs is mainly governed by solvent nature, temperature, co-solvent effects, and polymer concentration. These factors determine solvent viscosity, hydrogen-bond basicity, ion mobility, mass transport, and cellulose chain reassembly, thereby influencing both dissolution efficiency and the subsequent gel structure.

3.1.1 Solvent nature of ILs

Most studies indicate that cellulose dissolution is primarily driven by anions with strong hydrogen-bond-accepting ability, while cations contribute indirectly by stabilizing cellulose chains and regulating the local solvent environment. In imidazolium-based ILs, for example, the anion can form hydrogen bonds with the hydroxyl groups of cellulose, particularly around the C3 and C6 positions, leading to progressive disruption of interchain hydrogen bonding and cellulose dissolution (Novoselov et al., 2007; Fernandes et al., 2011; Ebner et al., 2008).

The hydrogen-bond basicity of anions is therefore a key parameter for evaluating cellulose dissolution ability. ILs containing weakly basic anions, such as BF₄ ⁻ and PF₆ ⁻, are generally ineffective for cellulose dissolution, whereas chloride- and acetate-based ILs exhibit stronger dissolution ability because of their higher hydrogen-bond acceptability (Feng and Chen, 2008; Kosan et al., 2008). Solvatochromic studies further suggest that the β value of anions is strongly correlated with cellulose solubility and can be used as an indicator for solvent design (Xu et al., 2010). The dissolution of cellulose in 1-ethyl-3-methylimidazolium chloride [EMIM][Cl] was studied, and no involvement of the C-C bond was observed. Instead of this, it was found that depolymerization of solubilized cellulose into glucose and levoglucosan, etc., occurred (Ohno and Miyafuji, 2013; Ding et al., 2012).

Moreover, anions of ILs with strong hydrogen bond acceptability, when combined with microwave heating, were found to be very effective in dissolving cellulose. The chloride-containing ILs system was also found to be an effective solvent, solubilizing cellulose through hydrogen bonding from the hydroxyl function to the anion of the solvents (Swatloski et al., 2002).

Further, acid-base conjugated ILs were prepared by the combination of different superbases with organic acids. It has the capability to dissolve cellulose quickly and also recycle with a high efficiency of 99% purity after every recycle (Parviainen et al., 2013; George et al., 2015). More commonly used ILs having dissolving capacity of more than 30g cellulose per mole of IL are shown below in Figure 1A, while the molecular structure of most commonly used ILs is shown in Figure 1B (Li et al., 2018; Gericke et al., 2012).

The cation structure also affects cellulose dissolution by influencing viscosity, polarity, steric hindrance, and solvent organization. For imidazolium-based cations, increasing alkyl-chain length or molecular symmetry usually decreases the dissolution rate because of increased viscosity and reduced hydrogen-bond acidity (Zhang et al., 2017). ILs have a huge impact on the proper functioning of cellulose-based ionogels, and by varying the content of ILs, the properties like conductivity and viscoelasticity can be adjusted and optimized (Swatloski et al., 2002; Lee et al., 2021; Sugimoto et al., 2021; Watanabe, 2021; Jiang et al., 2022; Zhao et al., 2022; Zhao et al., 2020; Wang et al., 2012; Wang X. et al., 2020).

In general, the dissolution ability of ILs with different cations follows the approximate order: imidazolium-based ILs > pyridinium-based ILs > ammonium-based ILs. For anions, the dissolution ability is more specific and depend on both hydrogen-bond basicity and the overall cation–anion combination. However, this is a general order made from experimental results obtained and solubility depends on both cationic and anionic structures as well as the externally provided conditions (Li et al., 2018).

The water content is another critical factor. Excessive water hydration weakens the ability of ILs to disrupt cellulose hydrogen bonding, thereby reducing dissolution efficiency. For example, highly hydrated solvent systems often lose their capacity to break the intermolecular hydrogen-bonding of cellulose. Therefore, effective cellulose-dissolving ILs should possess high hydrogen-bond basicity, appropriate viscosity, strong solvation ability, and controlled water content. These factors jointly determine dissolution kinetics, cellulose chain separation, and the formation of homogeneous cellulose-based ionogel networks (Zhong et al., 2012) (Mohd et al., 2017; Kader, 2014).

Therefore, in summary, the effective ILs must possess high hydrogen bond basicity to disrupt the hydrogen bonding efficiently in the cellulose structure. In ILs, anions such as chlorides and acetate play a significant role in showing superior dissolution and facilitating chain separations. Likewise, weakly basic anions such as PF₆ ⁻, BF₄ ⁻ are poor in dissolution. The cation has an influence on the viscosity, stability and polarity of ILs. Higher viscous solvents hinder the mass transport and reduce the dissolution kinetics, while moderately viscous solvents favor efficient solvation. (Zhang et al., 2012; Swatloski et al., 2002; Pinkert et al., 2009).

3.1.2 Temperature

Temperature is an important thermodynamic parameter that affects solvent viscosity, molecular mobility, mass transport, and interaction strength. During cellulose dissolution, increasing temperature generally enhances cellulose solubility by reducing solvent viscosity and accelerating diffusion. This facilitates solvent penetration into crystalline regions and promotes the disruption of cellulose hydrogen bonding. However, excessively high temperatures may induce cellulose degradation or side reactions in ionic-liquid systems, thereby compromising the structural integrity and final gel properties (Zhu et al., 2006; Remsing et al., 2006).

The temperature also plays a complementary role during gelation. As the system cools, reduced thermal energy weakens cellulose–solvent interactions and promotes the re-establishment of intermolecular hydrogen bonding between cellulose chains. This chain reassociation, together with physical entanglement, leads to the formation of a three-dimensional gel network. The cooling profile strongly affects the rate and uniformity of gelation: rapid cooling may generate heterogeneous networks, whereas controlled cooling favors more homogeneous gel structures. Therefore, temperature regulation is essential not only for efficient cellulose dissolution but also for controlled gelation and network formation (Gericke et al., 2012; Wang et al., 2012; Hina et al., 2015).

3.1.3 Co-solvents and polymer concentration

The co-solvents are often introduced as secondary solvents to tune the dissolution and gelation behavior of cellulose in ILs. Suitable co-solvents, usually polar organic liquids, can reduce solvent viscosity, improve mass transport, and promote more uniform cellulose dissolution. At low concentrations, they facilitate solvent penetration and hydrogen-bond disruption. However, excessive co-solvent content may compete with cellulose for hydrogen-bonding interactions, weaken the solvating ability of ILs, and lead to incomplete dissolution. Therefore, co-solvent dosage must be carefully optimized to balance dissolution efficiency, solution homogeneity, and gelation behavior. Co-solvents also regulate gelation by modulating the reversibility of cellulose–solvent interactions. Controlled solvent exchange reduces cellulose–solvent affinity, promotes cellulose chain reassociation, and facilitates the formation of homogeneous gel structure (Wang et al., 2012; Tritt-Goc, 2017).

Polymer concentration is another key factor governing the transition from solution to gel. Higher cellulose concentrations generally produce stronger gels because of increased chain entanglement and network density, but they also increase solution viscosity and reduce processability. In contrast, excessively low cellulose concentrations may fail to provide sufficient chain overlap and structural support, resulting in weak gelation. Therefore, optimizing cellulose concentration is essential for balancing dissolution efficiency, gelation kinetics, mechanical strength, and ion transport in cellulose-based ionogels (Hina et al., 2015; Medronho et al., 2012; Hauru et al., 2012).

3.2 DES- and aqueous-based systems

Cellulose dissolution in aqueous systems has also been achieved using precooled alkali/urea solutions. These systems can dissolve cellulose within a short time and offer advantages such as low cost, relatively low environmental impact, and convenient processing. Their dissolution mechanism differs from that of non-aqueous solvents. At low temperatures, alkali hydrates interact with cellulose through hydrogen bonding, whereas urea hydrates self-assemble around cellulose chains and stabilize the dissolved state, resulting in a transparent and stable cellulose solution (Lue et al., 2007; Cai et al., 2007; Ye et al., 2017; Cai et al., 2008; Qi et al., 2008). In addition, chemically modified cellulose derivatives, such as carboxymethyl cellulose and methyl cellulose, can be directly dissolved in water because their substituted groups weaken the native hydrogen-bonding and improve water affinity.

The DES have also attracted increasing attention for cellulose dissolution because of their low cost, design flexibility, and environmental compatibility. Similar to ILs, their dissolution process mainly involves the disruption and reconstruction of hydrogen-bonding interactions. However, most DES still exhibit lower cellulose solubility than ILs, which limits their direct use in preparing highly concentrated cellulose solutions. Therefore, further optimization of hydrogen-bond acceptors, hydrogen-bond donors, water content, and processing conditions is required to improve their dissolution efficiency and expand their application in cellulose-based ionogel fabrication (Vorobiov et al., 2022; Häkkinen and Abbott, 2019; Satlewal et al., 2018; Wang et al., 2021; Chen et al., 2019).

3.3 Computational studies of cellulose-IL dissolution

Experimental studies provide important macroscopic evidence for cellulose dissolution, but they often cannot fully reveal the molecular-level interactions between cellulose and ILs. Computational approaches, including COSMO-RS, quantum chemical calculations, and molecular dynamics simulations, have therefore been widely used to clarify cellulose–solvent interactions, hydrogen-bond disruption, and chain-separation mechanisms (Kahlen et al., 2010; Casas et al., 2012; Casas et al., 2013; Liu et al., 2016). COSMO-RS has been particularly useful for screening ILs and predicting their cellulose-dissolving ability. Kahlen et al. examined more than 200 ILs and found that anions play a dominant role by accepting hydrogen bonds from cellulose hydroxyl groups (Kahlen et al., 2010). Similarly, Casas et al. evaluated the solubility of cellulose and lignin in 780 ILs and showed that favorable dissolution is associated with low activity coefficients and exothermic mixing behavior (Casas et al., 2012).

More recently, Liu et al. used COSMO-RS to design new ILs for cellulose dissolution and experimentally confirmed that the predicted ILs exhibited improved dissolving capability. Their results further demonstrated that hydrogen bonding between cellulose and anions is the key driving force for dissolution (Liu et al., 2016). They found and prepared seven different types of ILs that have the potential to better solubilize cellulose, as shown in Figure 2A. The experimental results of dissolution aligned with the results as predicted by the computational model, and from the calculated excess enthalpy, it was also observed that H-bonds between cellulose and anions played a key role in dissolving cellulose. The molecular dynamics simulations provide more detailed insight into the dissolution process at the atomic scale. Early simulations showed that ILs interact differently with cellulose depending on the degree of polymerization and ion structure (Derecskei and Derecskei-Kovacs, 2006).

In many systems, anions such as OAc⁻ and Cl⁻ form stable hydrogen bonds with cellulose hydroxyl groups and are difficult to replace by the original intramolecular hydrogen bonds of cellulose (Rabideau and Ismail, 2015). However, in the presence of a large amount of water, the stability of the H-bond conformation breaks as shown in Figure 2B (Li et al., 2018). More studies were developed to fully understand the realistic approach of dissolution of large cellulose microfibril, and for this, Zhang et al. studied microcrystalline cellulose dissolution in [AMIM][Cl] using Transmission electron microscope (TEM) (Luo et al., 2012). The process was followed by the destruction of cellulose filaments, then dispersion of cellulose filaments, and slow solubilization of cellulose, which leads to the formation of an irregular cellulosic chain and IL in a stabilized system.

Several molecular dynamics studies have further clarified the respective roles of anions and cations. For example, simulations using glucose as a cellulose model showed that Cl⁻ forms stable hydrogen bonds with hydroxyl groups, whereas the imidazolium cation is mainly distributed around the non-polar regions of glucose and contributes weaker stabilizing interactions (Youngs et al., 2006). The solvated glucose structure in [BMIM][Cl] is easy to understand by spatial distribution function (SDF) e.g., the distribution of [Cl] in first solvation shell in which three to four anions showed interaction with one glucose through hydrogen bonds while the imidazolium cation was distributed in upper and lower position of glucose in the second solvation shell as shown in Figure 2C (Li et al., 2018). Moreover, the hydrogen bond (between cellulose and anion) which was considered as the main source of interaction energy was confirmed by the calculated energy (Youngs et al., 2007). A series of interactions of [Cnmim][Cl] with the cellulosic chain was studied by Ismail et al. through MD simulations and found that the anion interacted with the polar region of the cellulose chain while the cation interacted with the non-polar region and formed a patchwork interaction model (Rabideau et al., 2014).

Gupta et al. compared the interactions of [BMIM][OAc] [BMIM][PF₆], and water with cellulose Iβ microfibrils. Their simulations showed that the number of interchain hydrogen bonds remained largely unchanged in water and [BMIM][PF₆], but decreased significantly in [BMIM][OAc], confirming that the disruption of interchain hydrogen bonds is a critical step in cellulose dissolution (Gupta et al., 2011). Many hydrogen bonds were formed among adjacent cellulose chains. It was observed that the number of hydrogen bonds remained unchanged when cellulose was in contact with water and [BMIM][PF₆], but the number reduced largely when in contact with [BMIM][OAc], which showed that breaking of interchain H-bonds by ILs is the crucial step in dissolution to begin, as shown in Figure 2D. It was also studied that a small quantity of water has no effect on the dissolution of cellulose. In Shi et al. further investigated cellulose dissolution in [EMIM][OAc]/water mixtures and found that small amounts of water had only limited influence, whereas increasing water content progressively weakened the ability of the ILs to disrupt cellulose hydrogen bonding (Shi et al., 2014) Figure 2E.

Overall, computational studies suggest that cellulose dissolution in ILs involves progressive swelling, hydrogen-bond disruption, chain reorientation, and chain separation. Anions are generally regarded as the dominant species responsible for breaking cellulose hydrogen bonds, whereas cations contribute to solvent organization and stabilization of separated cellulose chains. Nevertheless, because many mechanistic conclusions are still mainly based on simulations, further experimental validation is necessary to establish a more reliable and quantitative understanding of cellulose–IL dissolution.

3.4 Regeneration pathways

After dissolution and gelation, cellulose can be regenerated from IL solutions using antisolvents such as water, ethanol, or acetone. Depending on the coagulation conditions and processing methods, regenerated cellulose can be obtained in various forms, including films, membranes, fibers, hydrogels, aerogels, and porous three-dimensional networks. These regenerated structures can also exhibit different thicknesses, crystallinities, pore architectures, and mechanical properties. Representative regenerated cellulose films prepared using different ILs, including [AMIM][Cl] [BMIM][Cl], and [EMIM][Ac], are summarized in Table 1.

TABLE 1. Regenerated cellulose film produced using ILs for structural application (such as packaging). The degree of polymerization (DP) and crystallinity index (CI in %) are reported for both^S starting materials and^R regenerated films. Mechanical properties include^a tensile strength (MPa) and^b elastic modulus (GPa) (Szabó et al., 2023).

However, regenerated cellulose films are often brittle because of strong interchain hydrogen bonding and limited chain mobility. This limitation can be alleviated by introducing plasticizers such as sorbitol, glycerol, or carboxymethyl cellulose before regeneration in the cellulose–IL solution. These additives can form secondary interactions with cellulose chains, reduce excessive hydrogen-bond-driven rigidity, and improve film flexibility (Pang et al., 2013; Liu et al., 2013).

The effect of plasticizers on crystallinity and mechanical properties depends strongly on the IL and processing route. For example, regenerated cellulose films prepared from [EMIM][Ac] and [AMIM][Cl] may show different trends in crystallinity after plasticizer addition, but both systems can exhibit improved tensile strength because of newly formed secondary interactions between cellulose and plasticizer molecules. In contrast, when regenerated films prepared from [BMIM][Cl] are post-treated by immersion in a plasticizer solution, glycerol may reduce tensile strength while increasing elongation at break (Jin et al., 2012).

Therefore, regeneration is a critical step that determines the final structure and performance of cellulose-based ionogels. The choice of antisolvent, coagulation rate, solvent-exchange pathway, plasticizer addition, and post-treatment conditions collectively regulates cellulose chain reassociation, crystallinity, porosity, mechanical flexibility, and ionic-liquid confinement. Rational control of regeneration pathways is thus essential for constructing cellulose-based ionogels with balanced mechanical robustness, ionic conductivity, and long-term structural stability.

In summary, the dissolution and regeneration play a decisive role in defining an ultimate ionogels properties through continuous interactions and reconstructions at the molecular level. The dissolution-induced hydrogen bonding disruption and solvation define cellulose chain mobility and dispersion, which control regeneration-driven reassembly. As a result, cellulose chain reorganizes into a network with distinct crystallinity, junction density, and mesoscale architecture, rather than reverting to native structure. These structural features directly translate into macroscopic ionogel properties, where network density governs mechanical strength and toughness, porosity controls ionic transport pathway, and the balance between ordered and amorphous domains regulates flexibility and conductivity. Therefore, ionogels performance is encoded at the molecular level during dissolution, subsequently “locked in” during regeneration, establishing a direct structure-processing-property relationship.

4 Network architecture design

The network architecture of cellulose-based ionogels is governed by the dissolution-regeneration pathway of cellulose, and can be constructed through chain entanglement, regenerated crystalline domains, dynamic hydrogen bonding interactions, and co-crosslinking with poly (ILs) or functional monomers. Depending on the target application, cellulose-based ionogels can be designed through physical, chemical, or metal-ion-coordinated interactions. These network-forming strategies determine the structural stability, ion-transport pathways, mechanical strength, and dynamic adaptability of the resulting ionogels (Zhang et al., 2024; Morozova, 2024).

The physical networks are mainly formed through reversible non-covalent interactions, chemical networks rely on covalent crosslinking to provide permanent structural stability, and metal-ion-coordinated networks introduce dynamic coordination bonds that combine reinforcement with reversible adaptability. Therefore, rational network architecture design is essential for balancing mechanical robustness, ionic mobility, self-healing ability, and long-term operational stability in cellulose-based ionogels.

4.1 Physical networking

Physical networking in cellulose-based ionogels is mainly based on reversible non-covalent interactions, including hydrogen bonding, van der Waals forces, hydrophobic interactions, ionic interactions, and chain entanglement. These interactions are essential for cellulose dissolution, regeneration, and gel formation. The first physically crosslinked cellulose-based ionogel was reported by Kadokawa in 2008. In this work, a concentrated cellulose solution was prepared by dissolving 15 wt% cellulose in [BMIM][Cl] at 100 °C for 24 h, followed by gel formation between glass slides over 7 days. The resulting gel was washed with ethanol to remove unconfined ILs, while a considerable amount of ILs and water remained trapped within the cellulose network (Kadokawa et al., 2008; Kavanagh and Ross-Murphy, 1998). However, the physically crosslinked cellulose-based ionogels that were made by using a similar approach to Kadokawa are summarized in Table 2(Szabó et al., 2023).

TABLE 2. Preparation of physical crosslinking of ionogels by dissolving cellulose in ILs (Szabó et al., 2023).

The formation of physically crosslinked cellulose ionogels generally begins with the disruption of native cellulose hydrogen bonds by ILs. The anions and cations of ILs interact with cellulose hydroxyl groups, enabling cellulose chain separation and dissolution. During water-induced regeneration, cellulose becomes thermodynamically unstable in the solvent-rich phase and gradually reassociates through inter- and intramolecular hydrogen bonding. This process leads to chain aggregation, physical entanglement, and the formation of cellulose-rich domains that act as physical crosslinking points, Figure 3A. The resulting cellulose network confines ILs within the gel matrix and forms a self-supporting ionogel (Wu et al., 2024; Haq et al., 2019; Wang et al., 2023) (Yue et al., 2021; Zheng et al., 2019; Deng et al., 2022). Due to insolubility in water, regenerated cellulose undergoes aggregation, and as a result, chain entanglement, self-support and reconstruction of inter- and intra-molecular hydrogen bonds occur in cellulose-rich dense phase. This makes a cellulose-cellulose network that traps the IL and forms an ionogel through a physical self-assembly approach, Figure 3B (Deng et al., 2022; Hopson et al., 2022). The cellulose-based ionogels have been made by such continuous aggregation and solidification of cellulose chains, and the rate of absorption of water has a significant effect on the resulting performance of cellulose ionogels (Chen et al., 2022). Further, the cellulose derivatives like carboxymethylated cellulose nanofibers (CNF), hydroxypropyl cellulose (HPC), and methylated cellulose (MC) can also be dissolved in suitable ILs by following a similar way of dissolution and cross-linking to form cellulose-based ionogel.

As, the physical crosslinks are reversible, physically crosslinked cellulose-based ionogels often exhibit good processability, recyclability, and thermoresponsive behavior. For example, some physically crosslinked ionogels can revert to a fluid state at elevated temperatures because of the dissociation of non-covalent interactions. However, their mechanical strength and long-term dimensional stability are usually lower than those of chemically crosslinked systems. Therefore, controlling cellulose concentration, solvent exchange rate, regeneration conditions, and ionic-liquid confinement is crucial for improving the structural integrity of physically crosslinked cellulose-based ionogels (Villar-Chavero et al., 2019; Smith et al., 2017a).

The cellulose derivatives, such as carboxymethylated cellulose nanofibers, hydroxypropyl cellulose, and methyl cellulose, can also be used to construct physically crosslinked ionogels through similar dissolution–regeneration and self-assembly processes. In addition, co-solvent evaporation and solvent-exchange strategies have been developed to introduce ILs into preformed cellulose networks, further expanding the design space of physically crosslinked cellulose-based ionogels. These materials have shown promise in electronic skins, smart devices, and soft scaffolds (Zhao et al., 2020; Villar-Chavero et al., 2019).

4.2 Chemical networking

In chemically crosslinked cellulose-based ionogels, covalent bonds are introduced between cellulose, ILs, monomers, or additional polymeric components to form permanent three-dimensional networks. Compared with physical networks, chemically crosslinked networks generally exhibit higher mechanical strength, better dimensional stability, and improved resistance to solvent leakage. Chemical crosslinking is commonly triggered by heat, ultraviolet irradiation, gamma irradiation, or free-radical polymerization. These methods enable grafting, polymerization, condensation, and crosslinking reactions within the cellulose–IL system.

Several representative strategies have been developed for constructing chemically crosslinked cellulose-based ionogels. For example, phosphorylated microcrystalline cellulose has been combined with 2-hydroxyethyl methacrylate monomers and polymerized through free-radical polymerization using N, N′-methylenebisacrylamide as a crosslinker and benzoyl peroxide as an initiator. The resulting chemically crosslinked ionogel was used to fabricate flexible symmetric supercapacitors, which could operate at 2.5 V over a broad temperature range in Figure 4A. Therefore, chemical crosslinking ionogels can be synthesized by triggering radiations (UV light, gamma radiation) to initiate reactions which include altering, polymerizing, grafting and degrading polymers, which ultimately leads to crosslinking, combining and building new bonds to develop a three-dimensional structure. The phenomenon of dehydrogenation and depolymerization of cellulose glycosidic bonds is behind the construction of chemically crosslinked cellulose ionogel. These phenomena require light/radiation to initiate the crosslinking process; thus, most of the chemical crosslinking of cellulose ionogel depends on light-initiated radical polymerization reactions. For example, the chemical crosslinking ionogels were made via in-situ photopolymerization of acrylic acid, cellulose and ILs, as shown in Figure 4B.

The photopolymerization is another widely used approach. Cellulose, acrylic acid, ILs, and photo initiators can be polymerized in situ under ultraviolet light to form chemically crosslinked ionogels. Similarly, ionogels can be prepared by photopolymerizing cellulose with ionic-liquid monomers, such as cholinium lactate methacrylate, in the presence of photo initiators. These light-initiated reactions enable rapid network formation and are particularly suitable for fabricating flexible electronic materials with controlled shapes and structures Figure 4C.

Although covalent crosslinking improves mechanical stability, it often reduces reversibility, recyclability, and component mobility. To address this limitation, dynamic covalent chemistry has been introduced into chemically crosslinked cellulose-based ionogels. For example, Schiff base reactions between aldehyde-modified cellulose and amino-containing polymers can generate reversible C=N bonds. Such dynamic covalent networks can combine mechanical robustness with self-healing ability and partial recyclability, making them attractive for flexible sensors and wearable electronics, as shown in Figure 4D.

Overall, the chemically crosslinked cellulose-based ionogels provide strong and stable networks, but their design must balance crosslinking density, ionic mobility, flexibility, and dynamic adaptability. Too much crosslinking restricts ionic conductivity, whereas insufficient crosslinking compromises structural integrity. Therefore, controlled chemical networking is essential for developing cellulose-based ionogels with both mechanical durability and electrochemical functionality. Commonly used methods for physical and chemical networks are shown in Figure 5 (Jiang et al., 2025).

4.3 Metal-ion coordinated networking

Metal-ion-coordinated networking provides another effective strategy for constructing cellulose-based ionogels. In these systems, multivalent metal ions coordinate with hydroxyl groups on cellulose or with other coordinating functional groups within the polymer matrix. These coordination interactions are stronger and more directional than many physical interactions, while still retaining a degree of reversibility and dynamic adaptability. As a result, metal-ion coordination can reinforce the cellulose network without completely suppressing stress relaxation or ion migration (Yang et al., 2026; Han et al., 2022).

The performance of metal-ion-coordinated cellulose-based ionogels depends strongly on the type of metal ion, coordination strength, ligand environment, and network microstructure. For instance, Ca²⁺-coordinated cellulose ionogels have been reported to achieve a tensile strength of 6.84 MPa and an ionic conductivity of 31.7 mS cm^-1. These ionogels also maintained flexibility at −196 °C, indicating that metal-ion coordination can simultaneously enhance mechanical robustness, ionic conductivity, and low-temperature tolerance (Bai et al., 2025).

Compared with purely physical or chemical networks, metal-ion-coordinated networks offer an intermediate strategy. They provide stronger reinforcement than reversible physical interactions while avoiding the complete rigidity of permanent covalent networks. This dynamic reinforcement mechanism is particularly valuable for flexible electronics, where materials must withstand repeated deformation while maintaining stable ion transport. Therefore, metal-ion coordination is a promising route for designing cellulose-based ionogels with integrated strength, toughness, conductivity, and environmental adaptability (Yang et al., 2026). The design strategies, interactions, properties, and applications of cellulose-based ionogels are summarized in Table 3.

TABLE 3. Design strategies, interactions, properties and applications of cellulose-based ionogels.

5 Structure-property coupling

The overall performance of cellulose-based ionogels arises from the hierarchical organization of cellulose and its interactions with confined ionic media. At the structural level, cellulose chains interact with ILs through hydrogen bonding, ion–dipole interactions, and dispersive forces. These interactions immobilize the liquid phase within the polymer matrix, suppress leakage and evaporation, and preserve localized ion mobility for efficient charge transport.

The cellulose scaffold provides dimensional stability, whereas the confined ions enable ionic conduction. This structure-guided synergy allows cellulose-based ionogels to function as quasi-solid electrolytes and multifunctional soft materials for flexible electronics, electrochemical devices, and wearable systems. However, an optimal balance between structural confinement and ionic mobility is essential. Excessive densification may restrict ion transport, whereas insufficient structural integrity can cause mechanical failure or liquid exudation. Therefore, precise control over cellulose microstructure, ionic-liquid confinement, and interfacial interactions is critical for maximizing the functional performance of cellulose-based ionogels.

5.1 Dynamic adhesion and self-healing

Flexible electronic materials with self-healing capability have attracted increasing interest, particularly for artificial electronic skin and wearable sensing systems. Integrating self-healing ability with mechanical flexibility, ionic conductivity, and adhesion can extend device lifetime and improve operational reliability. However, it remains challenging to fully recover tensile strength, flexibility, and conductivity after damage and healing (Benight et al., 2013).

The self-healing strategies are generally classified into extrinsic and intrinsic approaches. Extrinsic self-healing relies on pre-embedded repair agents, such as microcapsules or microvascular networks, which release healing components after damage. In contrast, intrinsic self-healing is based on reversible interactions within the polymer matrix, including hydrogen bonding, van der Waals interactions, electrostatic interactions, ionic interactions, and dynamic covalent bonds. These reversible interactions allow damaged interfaces to reconnect without the need for external healing agents (Zhang et al., 2021; Ekeocha et al., 2021). Recent studies have demonstrated that cellulose-based ionogels can combine self-healing, adhesion, mechanical robustness, and thermal stability through rational structural design. For example, a multifunctional three-dimensional ionogel prepared by photopolymerization exhibited a tensile strength of 1.28 MPa, an elongation at break of 573%, an initial decomposition temperature above 250 °C, and strong adhesion. Its adhesive strength increased from 2.23 to 4.23 MPa after 60 s of UV irradiation, depending on cellulose content, indicating effective non-covalent interactions with the glass surface, as shown in Figures 6A–C. The adhesion performance depends strongly on cellulose content and irradiation time. Increasing cellulose content can enhance interfacial interactions up to an optimal level, but excessive cellulose concentration may reduce ion mobility and flexibility. Similarly, insufficient UV exposure results in a low polymerization degree and weak cohesion, whereas excessive exposure may form overly long or rigid polymer chains. The optimized cellulose-based ionogel also showed adhesion to various substrates, including stainless steel, ceramics, PTFE, paper, wood, polystyrene, glass, polypropylene, and skin, suggesting its potential for human-motion monitoring and wearable sensing applications is shown in Figures 6D–F (Jian et al., 2025). The different types of cellulose-based ionogels with their self-healing and adhesive properties, along with their applications, are summarized in Table 4.

TABLE 4. Different types of cellulose-based ionogels with their self-healing, adhesive properties and applications.

Overall, dynamic adhesion and self-healing in cellulose-based ionogels are governed by the balance between reversible bonding, polymer-chain mobility, ionic-liquid confinement, and network strength. A well-designed dynamic architecture can provide autonomous damage repair and stable interfacial contact while maintaining mechanical compliance and ionic conductivity.

5.2 Thermal-structural integrity

Cellulose-based ionogels exhibit thermal stability and structural integrity because of the synergistic interaction between the cellulose framework and confined ILs. Cellulose provides structural support at elevated temperatures, whereas ILs, with negligible vapor pressure and high thermal resistance, suppress evaporation, leakage, and flammability.

A representative cellulose-based ionogel with programmable mechanical switching behavior was prepared through in-network copolymerization of N, N-dimethylacrylamide and hydroxyethyl methacrylate. In this system, cellulose acted as a molecular regulator because of its abundant hydroxyl groups and high solubility in [BMIM][Cl]. Through competitive interactions, cellulose induced the formation of ordered ionic-liquid crystalline domains, while the switching behavior was governed by a reversible crystallization–melting transition. This process was fast and reversible, providing the ionogel with pronounced switching ability and adaptive reconfigurability for soft robotics and responsive devices, as shown in Figure 7A.

The Cel-BF₄ ionogel showed a decomposition temperature of 480 °C, much higher than that of the reference Cel-IL gel at 291 °C. This improvement was attributed to the strengthened internal hydrogen-bonding. Moreover, the ionogel retained more than 80% of its volume over a broad temperature range from −18 °C to 120 °C and maintained flexibility after prolonged exposure to elevated temperatures, Figures 7B–D (Wang et al., 2026). The transparency, folding, and twisting capability of the Cel-BF4 gel are shown in Figure 7E.

Therefore, thermal–structural integrity in cellulose-based ionogels is controlled by cellulose structural stability, ionic-liquid confinement, hydrogen-bond density, and phase-transition behavior. These features are particularly important for flexible electronics operating under variable temperature, mechanical deformation, and long-term service conditions.

5.3 Conductivity and electrochemical window

Cellulose-based ionogels are promising flexible quasi-solid electrolytes because they combine ionic conductivity with electrochemical stability. A broad electrochemical stability window allows devices to operate safely over a wide voltage range, while efficient ion transport helps maintain low internal resistance and fast signal response.

In cellulose-based ionogels, ionic conductivity is determined by the type and content of IL, the continuity of ion-transport pathways, the degree of cellulose confinement, and the mobility of ions within the polymer network. The cellulose framework must be sufficiently robust to immobilize the IL and prevent leakage, but not so dense that it suppresses ion migration. Therefore, conductivity is closely coupled with porosity, polymer concentration, ion–polymer interactions, and residual solvent or water content.

For example, ionogels prepared from microcrystalline cellulose, sodium bentonite, and [BMIM][Ac] exhibited tunable electrical conductivity. Their conductivity increased by three to four orders of magnitude as the temperature rose from −30 °C to 80 °C. The conductivity also depended on microcrystalline cellulose content: the [BMIM][Ac]/Na-Bent/MCC-2 ionogel showed the highest conductivity, whereas further increasing MCC content generally reduced conductivity because of stronger network confinement and reduced ion mobility. A similar conductivity maximum was observed in systems without sodium bentonite when the MCC content was 2%.

These results indicate that cellulose content must be carefully optimized to balance mechanical reinforcement and ion transport. Moderate cellulose loading can construct a stable ion-conductive framework, whereas a high concentration of cellulose may restrict ionic mobility. Thus, the rational design of cellulose–IL interactions is essential for achieving high conductivity, broad electrochemical stability, and reliable device-level performance, as shown in Figures 8A–C (Alekseeva et al., 2023).

5.4 Mechanical strength

Mechanical strength is a critical requirement for cellulose-based ionogels used in long-term flexible and wearable applications. To withstand repeated stretching, bending, compression, and twisting, these materials must combine high strength, toughness, elasticity, and fatigue resistance. Considerable efforts have therefore focused on reinforcing cellulose-based ionogels through strengthened polymer networks, nanocellulose reinforcement, chemical crosslinking, and strong intermolecular interactions.

Nanocrystalline cellulose-based ionogels provide a representative example of mechanical reinforcement. In these systems, a crosslinked P (AM-co-AA) network provides elasticity and toughness, while partially solvated nanocrystalline cellulose chains form hydrogen bonds with the polymer matrix and ILs. The crystalline domains of nanocrystalline cellulose act as reinforcing units, improving mechanical strength, stretchability, and toughness.

The mechanical behavior of these ionogels depends strongly on nanocrystalline cellulose loading. Increasing nanocrystalline cellulose content enhances fracture strength, Young’s modulus, and fracture energy. However, excessive nanocrystalline cellulose can reduce elongation at break by restricting polymer-chain mobility. In the reported system, the ionogel containing 15 wt% nanocrystalline cellulose showed the highest toughness, while higher loadings provided stronger reinforcement and crack resistance but reduced stretchability as shown in Figures 9A–D (Shan et al., 2023).

The chemical crosslinking offers another effective route to improve mechanical robustness. A chemically crosslinked robust cellulose ionogel showed superior tensile behavior compared with the original uncrosslinked cellulose ionogel because glutaraldehyde-induced covalent bonding formed a stable cellulose framework. Its tensile strength reached 11 MPa, approximately ten times higher than that of the un-crosslinked cellulose ionogel as shown in Figures 9E–G (Yang et al., 2025).

Overall, the mechanical performance of cellulose-based ionogels is governed by crosslinking density, nanocellulose loading, hydrogen-bonding interactions, crystalline reinforcement, and polymer-chain mobility. The key challenge is to enhance strength and toughness without sacrificing stretchability, ionic conductivity, and dynamic adaptability.

6 Flexible applications

Cellulose-based ionogels have shown broad application potential in flexible electronics, soft actuators, wearable sensors, bio-inspired electronic skins, robotics, electrochemical devices, and energy-related systems. Their application value arises from the integration of mechanical compliance, ionic conductivity, environmental stability, processability, and structural tunability. In particular, the cellulose provides mechanical support and deformation tolerance, while the confined IL enables efficient ion transport and electrical responsiveness. These synergistic features allow cellulose-based ionogels to bridge material-level design and device-level performance in next-generation flexible systems.

6.1 Actuators

In smart electronic material systems, actuators serve as key components that convert external energy inputs into mechanical motion. Soft actuators require materials that can generate rapid, reversible, and stable deformation under low driving voltage while maintaining mechanical flexibility and structural integrity. Owing to their ionic conductivity, deformable structure, and liquid-retention capability, cellulose-based ionogels are used in ionic actuators.

The actuation behavior of cellulose-based ionogels is generally associated with ion migration, charge accumulation, electrochemical polarization, and asymmetric swelling within the device. Under an applied electric field, mobile ions redistribute across the ionogel matrix and induce volume changes or stress gradients, thereby generating bending or displacement. The cellulose framework contributes to mechanical support and dimensional stability, whereas the IL provides mobile charge carriers for electroresponsive deformation.

For example, electrodes with strong adhesion to electrolyte layers have been fabricated by combining cellulose nanofibers, ILs, and PEDOT: PSS. In this system, actuator motion mainly originates from swelling and expansion of the anode layer through a Faradaic-capacitive mechanism. The electrolyte type and anionic species also strongly influence actuation performance. Actuators based on lithium salts or 1-ethyl-3-methylimidazolium chloride can operate under direct-current voltages up to 5 V and achieve a bending strain of approximately 0.15% is shown in Figures 10A–C (Michinobu, 2023; Jia and Michinobu, 2023; Dayyoub et al., 2025). Figure 10D illustrates the electro-responsive behavior of the CCNF/IL/GN ionic actuator.

A major challenge for ionic actuators is achieving large, fast, and stable deformation at low voltage. This issue has been addressed by constructing highly electroactive actuator systems using carboxylated cellulose nanofibres, ILs, and graphene nanoplatelets. The resulting CCNF/IL/GN actuator achieved a tip displacement of 15.71 mm at 2 V, a response time of 2.9 s, and 98.6% performance retention over 3 h, demonstrating the potential of cellulose-based ionogels for low-voltage soft actuation.

Overall, cellulose-based ionogel actuators benefit from the combination of ion transport, flexible architecture, and interfacial stability. Future optimization should focus on increasing actuation strain, reducing response time, improving cycling stability, and clarifying the coupling between ionic redistribution, electrode reactions, and mechanical deformation.

6.2 Strain-pressure sensors

Flexible sensors represent a rapidly developing class of devices that can detect physical, chemical, and biological stimuli while conforming to complex and dynamic surfaces. Among them, strain and pressure sensors are particularly important for wearable electronics, human–machine interfaces, health monitoring, soft robotics, and electronic skin. Cellulose-based ionogels are well-suited for these applications because they combine mechanical deformability, ionic conductivity, interfacial adhesion, and environmental stability.

The sensing mechanism of cellulose-based ionogel sensors is mainly based on deformation-induced changes in ion transport, conductive pathways, and interfacial polarization. Under stretching, compression, or bending, the cellulose structure undergoes deformation, which changes the distance between ion-transport channels, the local ion concentration, and the resistance or capacitance of the device. These changes can be converted into electrical signals for real-time motion and pressure detection.

For strain sensing, cellulose-based ionogels must maintain stable conductivity under repeated tensile deformation. Their flexible polymer networks and reversible interactions help dissipate mechanical energy, reduce crack propagation, and preserve conductive pathways during stretching. For pressure sensing, the compressible ionogel design allows external pressure to modulate ion migration and electrode–electrolyte contact, resulting in measurable changes in resistance, capacitance, or voltage response.

Recently, a self-crosslinked cellulose ionogel (SCCel-ionogel) was successfully developed, which shows the potential to be used in sustainable flexible sensing applications, as shown in Figure 11A. The ionic conductivity of SCCel-ionogel was twice that of the ionic conductivity of cellulose-ionogel (Cel-ionogel), which established its feasibility in high-sensitivity sensor applications, as shown in Figure 11B. The Figure 11C shows the relative resistance of the material, which was adjusted in response to mechanical stimuli such as bending, compression, and tensile strain and also demonstrated a linear and proportional signal across various deformation modes. Moreover, the sensitivity of Cel-ionogel and SCCel-ionogel as sensors was figured out when attached to fingers and wrists by calculating the gauge factor (GF), which came out to be 1.82 and 16.307, respectively, which showed a linear relation between resistance changes and strain (Li et al., 2025).

In another study, Jiawei Yang et al. used a catalyst-free approach to develop a robust cellulose ionogel (RCI) and to test its performance. A portable pressure-sensing platform was constructed by integrating a signal acquisition module with a computer-based user interface, enabling real-time, accurate, and stable data output under various loading conditions Figure 11D. The RCI showed a linear relation between applied pressure and corresponding signal response under both low and high loadings. The calculated mean absolute error of RCI was nearly zero, while larger deviation was observed by commercially available polyvinylidene difluoride (PVDF) sensing material, e.g., at a low applied weight of 100 g, the mean absolute error was approximately 4 as shown in Figure 11E and this error increased to over 200 when weight input of 5,000 g was applied as shown in Figure 11F. Further, the RCI demonstrated outstanding repeatability by producing consistent and stable output signals under multiple testing, while both original cellulose (CI) and PVDF exhibited large signal fluctuations with significant baseline drift during ten consecutive test cycles, as shown in Figure 11G.

It was also noted that under small loads of below 20 g, PVDF was not sensitive to generate any response, while RCI showed accurate sensing output at low pressure. Moreover, a sensor array of 4 × 4 cm was fabricated to explore its capability in mapping external pressure distribution. The array allowed independent recognition of each sensing unit and accurate quantification of the applied load. The array displayed accurate output over a broad range of loadings, recording the values of 21, 202, and 2015 g in response to applied loads of 20, 200, and 2000 g, respectively, as shown in Figure 11H. In contrast, CI and PVDF displayed a large deviation of output signal to input pressure, and also PVDF was unable to detect light loads below 20 g (Yang et al., 2025).

However, several challenges remain. High sensitivity often requires a soft and deformable network, whereas long-term durability requires sufficient mechanical strength and structural stability. Therefore, future sensor design should balance sensitivity, response speed, detection range, mechanical durability, adhesion, and environmental stability.

6.3 Bio-inspired e-skin

The bio-inspired electronic skin requires soft materials that can mimic the flexibility, stretchability, conformability, and sensing ability of natural skin. These features are essential for wearable electronics, human–machine interaction, soft robotics, and health-monitoring devices. In this context, cellulose-based ionogels have emerged as promising platforms for biodegradable soft electronic devices because they integrate mechanical compliance, ionic stability, and tunable sensing performance.

A representative example is a cellulose/[BMIM][Cl] ionogel with dynamic and reversible properties controlled by water content. At a water content of 6 wt%, hydrogen bonding among cellulose and water leads to a loosely arranged Turing-type topological network. This structure exhibits relatively low ionic conductivity because of limited ion mobility, but it provides good self-healing and adhesion to substrates such as glass and plastics. When the water content increases to 32 wt%, a stronger Turing microstructure is formed, leading to improved strength and toughness Figure 12A. The generation of more hydrated ions at higher water content also enhances ionic conductivity, reaching up to 40 mS cm^-1 (Zhao et al., 2020).

Importantly, these two topological states can be reversibly switched by adjusting water content, allowing the ionogel to regulate its dynamic mechanical and electrical properties. Such adaptability is highly desirable for soft robotics, electronic skin, and flexible electronics. A practical e-skin device can be fabricated by sandwiching conductive layers between two ionogel films, enabling the detection of breathing, airflow, and touch signals Figure 12B (Szabó et al., 2023).

Overall, cellulose-based ionogels provide a promising material platform for bio-inspired e-skin because they combine soft mechanics, ionic signal transduction, self-healing ability, adhesion, and environmental stability. Future development should focus on improving multi-stimulus discrimination, long-term signal stability, device integration, biocompatibility, and scalable fabrication.

7 Challenges and future perspectives

Cellulose-based ionogels have shown great promise for flexible electronics, energy-storage devices, soft actuators, next-generation wearable electronics, electronic skin, and sensing systems owing to their biocompatibility, biodegradability, flexibility, self-healing capability, and structural tunability. However, despite these advantages, several key challenges must be addressed before their practical and large-scale application (Le Bideau et al., 2011; Smith et al., 2017b).

First, the dissolution and regeneration of cellulose remain central challenges. Although ILs are effective solvents for cellulose dissolution, many of them still suffer from high viscosity, high cost, complex purification procedures, and potential toxicity. These limitations increase processing difficulty and restrict scalable manufacturing. Therefore, future studies should focus on developing low-cost, recyclable, and environmentally benign solvent systems. In particular, more attention should be paid to green co-solvents and their roles in regulating cellulose dissolution, solvent viscosity, and chain reassembly (Li et al., 2018; Isik et al., 2014; Lu et al., 2014; Mostofian et al., 2011; Liu et al., 2010).

Second, the relationship among ionic-liquid composition, water content, viscosity, and cellulose dissolution efficiency requires a deeper understanding. Water can reduce solvent viscosity and improve processability, but excessive water may weaken cellulose–solvent interactions and reduce dissolution capability. Therefore, it is necessary to establish quantitative relationships between ionic-liquid structure, water content, viscosity, dissolution kinetics, and gel formation. Such understanding will be essential for designing efficient, economical, and recyclable cellulose–solvent systems (Verma et al., 2019; Isik et al., 2014; El Seoud et al., 2019).

Third, the trade-off between mechanical robustness and ionic conductivity remains a major limitation. Compared with many conventional polymer gels, cellulose-based ionogels show distinct advantages in structural stability and multifunctionality. However, increased densification or crosslinking may restrict ion migration, whereas insufficient structural integrity may lead to mechanical failure, liquid leakage, or poor long-term stability. Future research should therefore aim to optimize cellulose structural design, ionic-liquid confinement, and dynamic interactions to achieve simultaneous improvements in strength, toughness, conductivity, stretchability, and fatigue resistance (Anastas and Warner, 2000; Rogers and Seddon, 2003; Plechkova and Seddon, 2008).

Fourth, scalable fabrication and device integration remain underdeveloped. Practical applications require simple, reproducible, and low-energy processing methods that avoid toxic chemicals and undesired side reactions. Large-scale preparation also demands improved processability, stable ionic-liquid retention, controllable network uniformity, and reliable device-level performance. Therefore, future efforts should combine materials design with processing engineering, including continuous casting, printing, coating, solvent exchange, and encapsulation strategies.

Finally, the recycling and purification of ILs and antisolvents are crucial for the sustainable production of cellulose-based ionogels. During cellulose regeneration, water or other antisolvents must be efficiently separated from ILs with low energy consumption. Establishing closed-loop solvent-recycling systems would reduce cost, improve environmental compatibility, and support the development of cellulose-based ionogels in line with sustainable and green-chemistry principles.

In summary, future progress in cellulose-based ionogels should focus on green solvent systems, controllable dissolution–regeneration pathways, balanced mechanical and ionic performance, scalable processing, and sustainable solvent recovery. Addressing these challenges will enable cellulose-based ionogels to move from laboratory-scale demonstrations toward practical applications in flexible electronics, soft robotics, energy devices, and wearable sensing systems.

8 Discussion

The cellulose-based ionogels have attracted attention because of continuous progress in cellulose dissolution, mechanistic understanding, and flexible applications. Efficient dissolution in ILs, guided by solvent characteristics and enhanced by computational insights, leads to gelation driven by the reformation of intermolecular interactions, ultimately forming stable 3D networks.

The important parameters such as solvent nature, temperature, co-solvent and polymer concentration influence both dissolution and gelation, while with precise control, a uniform structure and optimal material properties can be achieved. Due to the multifunctional properties of cellulose-based ionogels, they have the potential for energy storage, flexible electronics, and soft robotic applications and represent a promising class of sustainable materials. Future efforts should be focused on the use of green solvents for more effective dissolution and improvement in process scalability to fully utilize the functional capabilities to enable broader utilization.

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Footnotes

Edited by: Xu Zeng, Huaqiao University, China

Reviewed by: Guihua Li, Qilu University of Technology Faculty of Mechanical Engineering, China

Dawei Zhao, Shenyang University of Chemical Technology, China