Ultrastretchable, Adhesive, Fast Self-Healable, and Three-Dimensional Printable Photoluminescent Ionic Skin Based on Hybrid Network Ionogels

Moisture-responsive ultralow-hysteresis polymer ionogels for adhesion-switchable strain sensing

Adhesion-switchable ultralow-hysteresis polymer ionogels are highly demanded in soft electronics to avoid debonding damage and signal distortion, yet the design and fabrication of such ionogels are challenging. Herein, we propose a novel method to design switchable adhesive ionogels by using binary ionic solvents with two opposite-affinity ionic components. The obtained ionogels exhibit moisture-induced phase separation, facilitating switchable adhesion with a high detaching efficiency (>99%). Moreover, before and after phase separation, the viscoelastic behavior of the ionogels is maintained in the rubbery plateau region within common frequency ranges with ultralow mechanical hysteresis (∼3%) under large strain, enabling accurate and stable strain and pressure sensing. Accordingly, the ionogel films can be used as functional elements in a smart clamp to realize flytrap-like selective activation, based on high sensitivity to the vibration intensity from the targeted prey. This work may inspire future research on the development of advanced soft electronics.

Ionogel Adhesives: From Structural Design to Emerging Applications

Adhesives are indispensable in both daily household applications and advanced industrial settings, where they must deliver exceptional bonding performance. Ionogel adhesives, which feature a supporting polymer network infused with ionic liquid (IL), have emerged as promising candidates due to their unique structural and functional properties. The presence of ionic species within ionogels promotes non-covalent interactions-such as ionic bonds, ion-dipole interactions, and hydrogen bonding-that enhance both cohesion within the material and adhesion to various substrates. These characteristics make ionogels ideal for applications that require robust adhesive performance, especially in demanding environments. Despite the growing interest in ionogel adhesives, a comprehensive review of the latest advancements in this area is lacking. This paper aims to fill this gap by categorizing ionogel adhesives based on their composition and discussing strategies to enhance their adhesive properties. Additionally, novel ionogel adhesives designed for specific applications are highlighted. Finally, the current state of research is summarized, and offers insights into the challenges and future opportunities for the development of ionogel adhesives.

Construction of gradient ionogels by self-floatable hyperbranched organosilicon crosslinkers for multi-sensing and wirelessly monitoring physiological signals

Monitoring complex human movements requires the simultaneous detection of strain and pressure, which poses a challenge due to the difficulty in integrating high stretchability and compressive ability into a single material. Herein, a series of hyperbranched polysiloxane crosslinkers (HPSis) with self-floating abilities are designed and synthesized. Taking advantage of the self-floating capabilities of HPSis, ionogels with gradient composition distribution and conductivities are constructed by in situ one-step photopolymerization, and possess satisfactory stretchability, high compressibility and excellent resilience. The gradient-ionogel-based strain sensor exhibits extraordinary pressure sensitivity (19.33 kPa-1), high strain sensitivity (GF reaches 2.5) and temperature sensing ability, enabling the monitoring of the angles and direction of joint movements, transmitting Morse code and wirelessly detecting bioelectrical signals. This study may inspire the design of development of multi-function flexible electronics.

Triboelectric nanogenerator based on silane-coupled LTA/PDMS for physiological monitoring and biomechanical energy harvesting

Energy harvesting from ambient sources present in the environment is essential to replace traditional energy sources. These strategies can diversify the energy sources, reduce maintenance, lower costs, and provide near-perpetual operation of the devices. In this work, a triboelectric nanogenerator (TENG) based on silane-coupled Linde type A/polydimethylsiloxane (LTA/PDMS) is developed for harsh environmental conditions. The silane-coupled LTA/PDMS-based TENG can produce a high output power density of 42.6 µW/cm2 at a load resistance of 10 MΩ and operates at an open-circuit voltage of 120 V and a short-circuit current of 15 µA under a damping frequency of 14 Hz. Furthermore, the device shows ultra-robust and stable cyclic repeatability for more than 30 k cycles. The fabricated TENG is used for the physiological monitoring and charging of commercial capacitors to drive low-power electronic devices. Hence, these results suggest that the silane-coupled LTA/PDMS approach can be used to fabricate ultra-robust TENGs for harsh environmental conditions and also provides an effective path toward wearable self-powered microelectronic devices.

Development and Performance Evaluation of Hybrid Iono-organogels for Efficient Impact Mitigation

Dissipative materials are essential for mitigating impact in various automotive, aerospace, and sports equipment applications. This study investigates the efficiency of a novel hybrid iono-organogel in dissipating and absorbing impact energies. The gel consists of a covalently cross-linked poly(acrylic acid)-co-poly(zwitterionic (DMAPS)) in a hybrid solvent system composed of the ionic liquid [C2OHMIM][BF4] and the oligomer PEG200. The optimal solvent hybridization ratio for achieving the lowest deceleration during impact testing is 40 vol % of the ionic liquid and 60 vol % of PEG200. The gel exhibits efficient mechanical dissipative properties with a loss factor exceeding 0.5 when solicited under various dynamic conditions with this optimized ratio. Moreover, the gel demonstrates high strength and toughness, enabling it to withstand impacts without experiencing catastrophic failure. The developed gel presents stable mechanical properties over broad temperature (0-100 °C) and frequency (0.01-2000 Hz) ranges. It maintains its performance during successive impacts, thanks to its self-recovery abilities. The remarkable mechanical properties of the gel are attributed to the abundance of combined functional groups within the gel polymeric network. Indeed, reversible H-bonds, ion-dipole, and dipole-dipole interactions were observed in different studies to enhance mechanical performance. Their unique synergy effect in the developed hybrid gels held promise for better control of impact properties and durability in numerous dynamic applications.

Review of ionic liquid and ionogel-based biomaterials for advanced drug delivery

Ionic liquids (ILs) play a crucial role in the design of novel materials. The ionic nature of ILs provides numerous advantages in drug delivery, acting as a green solvent or active ingredient to enhance the solubility, permeability, and binding efficiency of drugs. They could also function as a structuring agent in the development of nano/micro particles for drug delivery, including micelles, vesicles, gels, emulsion, and more. This review summarize the ILs and IL-based gel structures with their advanced drug delivery applications. The first part of review focuses on the role of ILs in drug formulation and the applications of ILs in drug delivery. The second part of review offers a comprehensive overview of recent drug delivery applications of IL-based gel. It aims to offer new perspectives and attract more attention to open up new avenues in the biomedical applications of ILs and IL-based gels.

Versatile ionic liquid gels formed by dynamic covalent bonding and microphase separated structures

It is challenging for ionic liquid gels to achieve the combination of rapid self-healing with high toughness. Here, ionic liquid gels (DI-PR) were prepared from readily available materials. A dynamic covalently bonded oxime-carbamate was prepared from polycaprolactone diol, isophorone diisocyanate and dimethylethyleneglyoxime, followed by addition of the "rigid-flexible" cross-linking agent rutin to chemically cross-link the polymer chains and afford the ionic liquid gels, DI-PR. The tensile strength, elongation at break and toughness of the DI-PR gels were as high as 16.5 MPa, 1132.6%, and 52.6 MJ m-3, respectively. The toughness is similar to that of natural silkworm silk (70 MJ m-3) and wool (60 MJ m-3). After stretching, the DI-PR can rebound within 1 s, their room temperature self-healing rate is as high as 92%, they remain functional over the temperature range -50 °C to 140 °C and the interface with a steel plate has an adhesion toughness of >2000 J m-2. These properties mean that the DI-PR gels are particularly suitable for use as anticorrosion coatings for submarine and underground gas and oil pipelines. The use of rutin, which combines rigid quercetin-based structural units with flexible glycoside-based structural units, as a cross-linking agent, provides a new method for improving the toughness of soft materials through its synergistic interaction with hard and soft chain fragments of polyurethanes.

Research Progress and Application of Multimodal Flexible Sensors for Electronic Skin

In recent years, wearable electronic skin has garnered significant attention due to its broad range of applications in various fields, including personal health monitoring, human motion perception, human-computer interaction, and flexible display. The flexible multimodal sensor, as the core component of electronic skin, can mimic the multistimulus sensing ability of human skin, which is highly significant for the development of the next generation of electronic devices. This paper provides a summary of the latest advancements in multimodal sensors that possess two or more response capabilities (such as force, temperature, humidity, etc.) simultaneously. It explores the relationship between materials and multiple sensing capabilities, focusing on both active materials that are the same and different. The paper also discusses the preparation methods, device structures, and sensing properties of these sensors. Furthermore, it introduces the applications of multimodal sensors in human motion and health monitoring, as well as intelligent robots. Finally, the current limitations and future challenges of multimodal sensors will be presented.

Skin-Inspired, Highly Sensitive, Broad-Range-Response and Ultra-Strong Gradient Ionogels Prepared by Electron Beam Irradiation

Skin, characterized by its distinctive gradient structure and interwoven fibers, possesses remarkable mechanical properties and highly sensitive attributes, enabling it to detect an extensive range of stimuli. Inspired by these inherent qualities, a pioneering approach involving the crosslinking of macromolecules through in situ electron beam irradiation (EBI) is proposed to fabricate gradient ionogels. Such a design offers remarkable mechanical properties, including excellent tensile properties (>1000%), exceptional toughness (100 MJ m-3), fatigue resistance, a broad temperature range (-65-200°C), and a distinctive gradient modulus change. Moreover, the ionogel sensor exhibits an ultra-fast response time (60 ms) comparable to skin, an incredibly low detection limit (1 kPa), and an exceptionally wide detection range (1 kPa-1 MPa). The exceptional gradient ionogel material holds tremendous promise for applications in the field of smart sensors, presenting a distinct strategy for fabricating flexible gradient materials.

Bioinspired Touch-Responsive Hydrogels for On-Demand Adhesion on Rough Surfaces

Reversible adhesives are widely needed in our daily lives and industrial applications. However, robust and switchable adhesion on rough surfaces with on-demand attachment and detachment remains highly challenging. Here, we report a snail-mucus-inspired touch-responsive hydrogel (TRH), whose universal and robust adhesion is triggered by simple contact with the attaching surface. TRH is composed of a polymeric hydrogel and saturated sodium acetate (NaAc) and is prepared by one-pot synthesis. At room temperature, TRH remains in an amorphous and soft state, which allows it to conformally adapt to rough surfaces. The contact with the target surface triggers the crystallization of NaAc, which increases the modulus of TRH by an order of magnitude and interlocks with the target surfaces, achieving an adhesion of up to 204.84 ± 53.98 kPa. Upon heating, TRH returns to a soft state, facilitating easy detachment with adhesion of 5.12 ± 1.34 kPa. Meanwhile, the detached TRH is ready for the next adhesion without the need to be maintained at high temperature. TRH finds applications as a smart material for light-triggered adhesion switching, information encryption, and temperature sensors.

Polymerized and Colloidal Ionic Liquids─Syntheses and Applications

The breadth and importance of polymerized ionic liquids (PILs) are steadily expanding, and this review updates advances and trends in syntheses, properties, and applications over the past five to six years. We begin with an historical overview of the genesis and growth of the PIL field as a subset of materials science. The genesis of ionic liquids (ILs) over nano to meso length-scales exhibiting 0D, 1D, 2D, and 3D topologies defines colloidal ionic liquids, CILs, which compose a subclass of PILs and provide a synthetic bridge between IL monomers (ILMs) and micro to macro-scale PIL materials. The second focus of this review addresses design and syntheses of ILMs and their polymerization reactions to yield PILs and PIL-based materials. A burgeoning diversity of ILMs reflects increasing use of nonimidazolium nuclei and an expanding use of step-growth chemistries in synthesizing PIL materials. Radical chain polymerization remains a primary method of making PILs and reflects an increasing use of controlled polymerization methods. Step-growth chemistries used in creating some CILs utilize extensive cross-linking. This cross-linking is enabled by incorporating reactive functionalities in CILs and PILs, and some of these CILs and PILs may be viewed as exotic cross-linking agents. The third part of this update focuses upon some advances in key properties, including molecular weight, thermal properties, rheology, ion transport, self-healing, and stimuli-responsiveness. Glass transitions, critical solution temperatures, and liquidity are key thermal properties that tie to PIL rheology and viscoelasticity. These properties in turn modulate mechanical properties and ion transport, which are foundational in increasing applications of PILs. Cross-linking in gelation and ionogels and reversible step-growth chemistries are essential for self-healing PILs. Stimuli-responsiveness distinguishes PILs from many other classes of polymers, and it emphasizes the importance of segmentally controlling and tuning solvation in CILs and PILs. The fourth part of this review addresses development of applications, and the diverse scope of such applications supports the increasing importance of PILs in materials science. Adhesion applications are supported by ionogel properties, especially cross-linking and solvation tunable interactions with adjacent phases. Antimicrobial and antifouling applications are consequences of the cationic nature of PILs. Similarly, emulsion and dispersion applications rely on tunable solvation of functional groups and on how such groups interact with continuous phases and substrates. Catalysis is another significant application, and this is an historical tie between ILs and PILs. This component also provides a connection to diverse and porous carbon phases templated by PILs that are catalysts or serve as supports for catalysts. Devices, including sensors and actuators, also rely on solvation tuning and stimuli-responsiveness that include photo and electrochemical stimuli. We conclude our view of applications with 3D printing. The largest components of these applications are energy related and include developments for supercapacitors, batteries, fuel cells, and solar cells. We conclude with our vision of how PIL development will evolve over the next decade.

Strain-Induced Phase Separation and Mechanomodulation of Ionic Conduction in Anisotropic Nanocomposite Ionogels

Ionogels have great potential for the development of tissue-like, soft, and stretchable ionotronics. However, conventional isotropic ionogels suffer from poor mechanical properties, low efficient force transmission, and tardy mechanoelectric response, hindering their practical utility. Here, we propose a simple one-step method to fabricate bioinspired anisotropic nanocomposite ionogels based on a combination of strain-induced phase separation and mechanomodulation of ionic conduction in the presence of attapulgite nanorods. These ionogels show high stretchability (747.1% strain), tensile strength (6.42 MPa), Young's modulus (83.49 MPa), and toughness (18.08 MJ/m3). Importantly, the liquid crystalline domain alignment-induced microphase separation and ionic conductivity enhancement during stretching endow these ionogels with an unusual mechanoelectric response and dual-programmable shape-memory properties. Moreover, the anisotropic structure, good elasticity, and unique resistance-strain responsiveness give the ionogel-based strain sensors high sensitivity, rapid response time, excellent fatigue resistance, and unique waveform-discernible strain sensing, which can be applied to real-time monitoring of human motions. The findings offer a promising way to develop bioinspired anisotropic ionogels to modulate the microstructure and properties for practical applications in advanced ionotronics.

Janus-type ionic conductive gels based on poly(N,N-dimethyl)acrylamide for strain/pressure sensors

Strain/pressure sensors with high sensitivity and a wide operation range have broad application prospects in wearable medical equipment, human-computer interactions, electronic skin, and so on. In this work, based on the different solubilities of Zr4+ in the aqueous phase and the hydrophobic ionic liquid [BMIM][Tf2N], we used N,N-dimethylacrylamide (DMA) as a vinyl monomer to prepare a Janus-type ionic conductive gel with one-sided adhesion through "one-step" UV irradiation polymerization. The Janus-type gel has satisfactory mechanical properties (tensile strength: 217.06 kPa, elongation at break: 1121.01%), electrical conductivity (conductivity: 0.10 S m-1), one-sided adhesion (adhesion strength to glass: 72.35 kPa) and antibacterial properties. The sensor based on the Janus gel can be used not only for real-time monitoring of strain changes caused by various movements of the human body (such as finger bending, muscle contraction, smiling, and swallowing) but also for real-time monitoring of pressure changes (such as pressing, water droplets, and writing movements). Therefore, based on the simplicity of this method for constructing Janus-type ionic conductive gels and the excellent electromechanical properties of the prepared gel, we believe that the method provided in this study has broad application prospects in the field of multifunctional wearable sensors.

Degradable Supramolecular Eutectogel-Based Ionic Skin with Antibacterial, Adhesive, and Self-Healable Capabilities

The development of degradable, cost-effective, and eco-friendly ionic conductive gels is highly required to reduce electronic waste originating from flexible electronic devices. However, biocompatible, degradable, tough, and durable conductive gels are challenging to achieve. Herein, we develop a facile strategy for the design and synthesis of degradable tough eutectogels by integrating an electrostatically driven supramolecular network composed of branched polyacrylic acid (PAA) and monoethanolamine (MEA) into a green deep eutectic solvent with chitosan quaternary ammonium salt (CQS). The specially designed PAA/MEA/CQS eutectogels present multiple desired properties, including high transparency, widely adjustable mechanical properties, high resilience, reliable adhesiveness, excellent self-healing ability, good conductivity, remarkable anti-freezing performance, and antibacterial properties. The dynamic and reversible supramolecular interactions not only significantly enhance the mechanical properties of the PAA/MEA/CQS eutectogels but also enable fast degradation, addressing the dilemma between mechanical strength and degradability. More importantly, a biocompatible and degradable multifunctional ionic skin is successfully fabricated based on the PAA/MEA/CQS eutectogel, exhibiting high sensitivity, a wide sensing range, and a rapid response speed toward strain, pressure, and temperature. Thus, this study offers a promising strategy for fabricating degradable tough eutectogels, which show great potential as high-performance ionic skins for next-generation flexible wearable electronic devices.

Eucalyptus bleached kraft pulp-ionic liquid inks for 3D printing of ionogels and hydrogels

3D printing has been recently recognized as one of the most promising technologies due to the multiple options to fabricate cost-effective and customizable objects. However, the necessity to substitute fossil fuels as raw materials is increasing the research on bio-based inks with recyclable and eco-friendly properties. In this work, we formulated inks for the 3D printing of ionogels and hydrogels with bleached kraft pulp dissolved in [Emim][DMP] at different concentrations (1-4 wt%). We explored each ink's rheological properties and printability and compared the printability parameters with a commercial ink. The rheological results showed that the 3 % and 4 % cellulose-ionic liquid inks exhibited the best properties. Both had values of damping factor between 0.4 and 0.7 and values of yield stress between 1900 and 2500 Pa. Analyzing the printability, the 4 wt% ink was selected as the most promising because the printed ionogels and the hydrogels had the best print resolution and fidelity, similar to the reference ink. After printing, ionogels and hydrogels had values of the elastic modulus (G') between 10³ and 10⁴ Pa, and the ionogels are recyclables. Altogether, these 3D printed cellulose ionogels and hydrogels may have an opportunity in the electrochemical and medical fields, respectively.

Stretchable and recyclable gelatin Ionogel based ionic skin with extensive temperature tolerant, self-healing, UV-shielding, and sensing capabilities

Fabricating sustainable ionic skin with multi-functional outstanding performances using biocompatible natural polymer-based ionogel is highly desired but remains a great challenge up to now. Herein, a green and recyclable ionogel has been fabricated by in-situ cross-linking of gelatin with a green bio-based multifunctional cross-linker of Triglycidyl Naringenin in ionic liquid. Benefiting from the unique multifunctional chemical crosslinking networks along with multiple reversible non-covalent interactions, the as-prepared ionogels exhibit high stretchability (>1000 %), excellent elasticity, fast room-temperature self-healability (>98 % healing efficiency at 6 min), and good recyclability. These ionogels are also highly conductive (up to 30.7 mS/cm at 150 °C), and exhibit extensive temperature tolerance (-23 to 252 °C) and outstanding UV-shielding ability. As a result, the as-prepared ionogel can easily be applied as stretchable ionic skin for wearable sensors, which exhibits high sensitivity, fast response time (102 ms), excellent temperature tolerance, and stability over 5000 stretching-relaxing cycles. More importantly, the gelatin-based sensor can be used in signal monitor system for various human motion real-time detection. This sustainable and multifunctional ionogel provides a new idea for easy and green preparation of advanced ionic skins.

Cross-Link-Dependent Ionogel-Based Triboelectric Nanogenerators with Slippery and Antireflective Properties

Given the ability to convert various ambient unused mechanical energies into useful electricity, triboelectric nanogenerators (TENGs) are gaining interest since their inception. Recently, ionogel-based TENGs (I-TENGs) have attracted increasing attention because of their excellent thermal stability and adjustable ionic conductivity. However, previous studies on ionogels mainly pursued the device performance or applications under harsh conditions, whereas few have investigated the structure-property relationships of components to performance. The results indicate that the ionogel formulation-composed of a crosslinking monomer with an ionic liquid-affects the conductivity of the ionogel by modulating the cross-link density. In addition, the ratio of cross-linker to ionic liquid is important to ensure the formation of efficient charge channels, yet increasing ionic liquid content delivers diminishing returns. The ionogels are then used in I-TENGs to harvest water droplet energy and the performance is correlated to the ionogels structure-property relationships. Improvement of the energy harvesting is further explored by the introduction of surface polymer brushes on I-TENGs via a facile and universal method, which enhances droplet sliding by means of ideal surface contact angle hysteresis and improves its anti-reflective properties by employing the I-TENG as a surface covering for solar cells.

Mechanically Robust and Room Temperature Self-Healing Ionogel Based on Ionic Liquid Inhibited Reversible Reaction of Disulfide Bonds

Although highly desired, it is difficult to develop mechanically robust and room temperature self-healing ionic liquid-based gels (ionogels), which are very promising for next-generation stretchable electronic devices. Herein, it is discovered that the ionic liquid significantly reduces the reversible reaction rate of disulfide bonds without altering its thermodynamic equilibrium constant via small molecule model reaction and activation energy evolution of the dissociation of the dynamic network. This inhibitory effect would reduce the dissociated units in the dynamic polymeric network, beneficial for the strength of the ionogel. Furthermore, aromatic disulfide bonds with high reversibility are embedded in the polyurethane to endow the ionogel with superior room temperature self-healing performance. Isocyanates with an asymmetric alicyclic structure are chosen to provide optimal exchange efficiencies for the embedded disulfide bonds relative to aromatic and linear aliphatic. Carbonyl-rich poly(ethylene-glycol-adipate) diols are selected as soft segments to provide sufficient interaction sites for ionic liquids to endow the ionogel with high transparency, stretchability, and elasticity. Finally, a self-healing ionogel with a tensile strength of 1.65 ± 0.08 MPa is successfully developed, which is significantly higher than all the reported transparent room temperature self-healing ionogel and its application in a 3D printed stretchable numeric keyboard is exemplified.

Ionogels: recent advances in design, material properties and emerging biomedical applications

Ionic liquid (IL)-based gels (ionogels) have received considerable attention due to their unique advantages in ionic conductivity and their biphasic liquid-solid phase property. In ionogels, the negligibly volatile ionic liquid is retained in the interconnected 3D pore structure. On the basis of these physical features as well as the chemical properties of well-chosen ILs, there is emerging interest in the anti-bacterial and biocompatibility aspects. In this review, the recent achievements of ionogels for biomedical applications are summarized and discussed. Following a brief introduction of the various types of ILs and their key physicochemical and biological properties, the design strategies and fabrication methods of ionogels are presented by means of different confining networks. These sophisticated ionogels with diverse functions, aimed at biomedical applications, are further classified into several active domains, including wearable strain sensors, therapeutic delivery systems, wound healing and biochemical detections. Finally, the challenges and possible strategies for the design of future ionogels by integrating materials science with a biological interface are proposed.

Self-Healing, Thermadapt Triple-Shape Memory Ionomer Vitrimer for Shape Memory Triboelectric Nanogenerator

Benefiting from the associative exchange reaction, vitrimers could be deformed to various shapes while maintaining the integrity of the network, thus being regarded as promising candidates for shape memory polymers. However, it is still a challenge to design the highly desired smart electronic devices with triple and multishape memory performances through a facile method. Here, a novel dual-cross-linked poly(acrylonitrile-co-butyl acrylate-co-hydroxyethyl methacrylate-co-zinc methacrylate) (Zn-PABHM) copolymer was developed via a facile and one-pot free radical polymerization strategy. Ionic cross-linking, the transcarbamoylation reaction, and glass transition were used to fix the permanent shape and two temporary shapes of the obtained ionomer vitrimer, respectively. The thermomechanical and stress relaxation performances of Zn-PABHM vitrimer can be customized by tuning the proportion of the chemical cross-linking and physical cross-linking knots. Furthermore, the Zn-PABHM was employed to construct a shape memory triboelectric nanogenerator, which demonstrates distinctive performance and tunable electrical outputs (37.4-96.0 V) due to variable contact areas enabled by triple shape memory effects. Consequently, the triple-shape memory ionomer vitrimer obtained via a facile and one-pot synthetic strategy has great potential in smart multifunctional electronic devices.

Recent Advances in Mechanical Reinforcement of Zwitterionic Hydrogels

As a nonspecific protein adsorption material, a strong hydration layer provides zwitterionic hydrogels with excellent application potential while weakening the interaction between zwitterionic units, leading to poor mechanical properties. The unique anti-polyelectrolyte effect in ionic solution further restricts the application value due to the worsening mechanical strength. To overcome the limitations of zwitterionic hydrogels that can only be used in scenarios that do not require mechanical properties, several methods for strengthening mechanical properties based on enhancing intermolecular interaction forces and polymer network structure design have been extensively studied. Here, we review the works on preparing tough zwitterionic hydrogel. Based on the spatial and molecular structure design, tough zwitterionic hydrogels have been considered as an important candidate for advanced biomedical and soft ionotronic devices.

Poly(N,N-dimethyl)acrylamide-based ion-conductive gel with transparency, self-adhesion and rapid self-healing properties for human motion detection

Flexible strain sensors have been extensively studied for their potential value in monitoring human activity and health. However, it is still challenging to develop multifunctional flexible strain sensors with simultaneously high transparency, strong self-adhesion, fast self-healing and excellent tensile properties. In this study, we used N,N-dimethylacrylamide (DMA) in the imidazolium-based ionic liquid 1-butyl-3-methylimidazolium bis[(trifluoromethyl)sulfonyl] imide ([BMIM][Tf₂N]) for "one-step" UV irradiation. A poly(N,N-dimethyl)acrylamide (PDMA) ion-conductive gel was prepared by site polymerization. Based on the good compatibility between PDMA and ionic liquid, the prepared ion-conductive gel has good transparency (∼90%), excellent stretchability (1080%), strong self-adhesion (67.57 kPa), fast self-healing (2 s at room temperature) and great antibacterial activity (∼99% bacterial killing efficiency). Moreover, the strain sensor based on the PDMA ion-conductive gel has good electromechanical performance and can detect different human motions. Based on the simple and easy-to-operate preparation method and the endowed multifunctionality of the PDMA ion-conductive gel, it has broad application prospects in the field of flexible electronic devices.

Dual Thermo-Responsive and Strain-Responsive Ionogels for Smart Windows and Temperature/Motion Monitoring

In this work, a stretchable, dual thermo-responsive and strain-responsive ionogel has been synthesized by one-step photopolymerization. The obtained ionogel shows an ultrahigh stretchability (∼3000%), a high ionic conductivity (up to 3.1 mS/cm), and a good temperature tolerance (-40 to 300 °C). Importantly, these ionogels show an upper critical solution temperature-type phase transition with a wide tunable phase-transition temperature (17.5-42.5 °C) and reversible color/transparency switching. In particular, the as-prepared ionogel-based flexible/wearable temperature monitors and smart windows show an excellent designability and programmability, temperature modulation ability, and thermal responsiveness. Moreover, the ionogels-based strain sensors have temperature- and strain-dual responsibility and a broad strain-sensing range (1-700%), which can effectively monitor various motions. This strategy of fabricating dual thermo- and strain-responsive ionogels by using a one-step method and only one polymer holds great promise for the next generation of multifunctional stimuli-responsive materials.