Self-healable poly(acrylic acid-co-maleic acid)/glycerol/boron nitride nanosheet composite hydrogels at low temperature with enhanced mechanical properties and water retention

Self-Healing Hydrogel Bioelectronics

Hydrogels have emerged as powerful building blocks to develop various soft bioelectronics because of their tissue-like mechanical properties, superior bio-compatibility, the ability to conduct both electrons and ions, and multiple stimuli-responsiveness. However, hydrogels are vulnerable to mechanical damage, which limits their usage in developing durable hydrogel-based bioelectronics. Self-healing hydrogels aim to endow bioelectronics with the property of repairing specific functions after mechanical failure, thus improving their durability, reliability, and longevity. This review discusses recent advances in self-healing hydrogels, from the self-healing mechanisms, material chemistry, and strategies for multiple properties improvement of hydrogel materials, to the design, fabrication, and applications of various hydrogel-based bioelectronics, including wearable physical and biochemical sensors, supercapacitors, flexible display devices, triboelectric nanogenerators (TENGs), implantable bioelectronics, etc. Furthermore, the persisting challenges hampering the development of self-healing hydrogel bioelectronics and their prospects are proposed. This review is expected to expedite the research and applications of self-healing hydrogels for various self-healing bioelectronics.

Nanoarchitectonics composite hydrogels with high toughness, mechanical strength, and self-healing capability for electrical actuators with programmable shape memory properties

Hydrogel materials show promise in various fields, including flexible electronic devices, biological tissue engineering and wound dressing. Nevertheless, the inadequate mechanical properties, recovery performance, and self-healing speed still constrain the development of intelligent hydrogel materials. To tackle these challenges, we designed a composite hydrogel with high mechanical strength, rapid self-recovery and efficient self-healing ability based on multiple synergistic effects. With the synergistic effect of hydrogen bonds, metal coordination bonds and electrostatic interaction, the synthesized hydrogel could reach a maximum tensile strength of 6.2 MPa and a toughness of 50 MJ m-3. The interaction between the weak polyelectrolyte polyethyleneimine and polyacrylic acid aided in improving the elasticity of the hydrogel, thereby endowing it with prompt self-recovery attributes. The multiple reversible effects also endowed the hydrogel with excellent self-healing ability, and the fractured hydrogel could achieve 95% self-healing within 4 h at room temperature. By the addition of glycerol, the hydrogel could also cope with a variety of extreme environments in terms of moisture retention (12 h, maintaining 80% of its water content) and freeze protection (-36.8 °C) properties. In addition, the composite hydrogels applied in the field of shape memory possessed programmable and reversible shape transformation properties. The polymer chains were entangled at high temperatures to achieve shape fixation, and shape memory was eliminated at low temperatures, which allowed the hydrogels to be reprogrammed and achieve multiple shape transitions. In addition, we also assemble composite hydrogels as actuators and robotic arms for intelligent applications.

Large-scale production of MXenes as nanoknives for antibacterial application

Antimicrobial resistance of existing antibacterial agents has become a pressing issue for human health and demands effective antimicrobials beyond conventional antibacterial mechanisms. Two-dimensional (2D) nanomaterials have attracted considerable interest for this purpose. However, obtaining a high yield of 2D nanomaterials with a designed morphology for effective antibacterial activity remains exceptionally challenging. In this study, an efficient one-step mechanical exfoliation (ECO-ME) method has been developed for rapidly preparing Ti3C2 MXenes with a concentration of up to 30 mg mL-1. This synthetic pathway involving mechanical force endows E-Ti3C2 MXene prepared by the ECO-ME method with numerous irregular sharp edges, resulting in a unique nanoknife effect that can successfully disrupt the bacterial cell wall, demonstrating better antibacterial activity than the MXenes prepared by conventional wet chemical etching methods. Overall, this study provides a simple and effective method for preparing MXenes on a large scale, and its antibacterial effects demonstrate great potential for E-Ti3C2 in environmental and biomedical applications.

Fabrication of an ion-enhanced low-temperature tolerant graphene/PAA/KCl hydrogel and its application for skin sensors

Flexible sensors based on conductive hydrogels show great potential in wearable displays and smart devices. However, a water-based hydrogel inevitably freezes or loses its conductivity under extremely cold temperatures, leading to inadequate fulfillment of sensor performance. Herein, a well-designed strategy is proposed for fabricating a low-temperature-tolerant water-based hydrogel for sensor applications. By immersing a multi-crosslinking graphene(GO)/polyacrylic acid (PAA)-Fe³⁺ hydrogel into a KCl solution, an ion-enhanced conductive (GO/PAA/KCl) hydrogel is obtained with excellent conductivity (24.4 S m^-1 at 20 °C; 16.2 S m^-1 at -20 °C; 0.8 S m^-1 at -80 °C) and outstanding antifreezing properties. The conductive hydrogel also possesses good mechanical properties with a fracture stress of 2.65 MPa and an elongation at break of 1511% and maintains its flexibility even at -35 °C. Then, a strain sensor is assembled to monitor the human motion at 20 °C and the movement of a wooden mannequin at -20 °C. Under both conditions, the sensor presents high sensitivity (GF = 8.66 at 20 °C, 7.93 at -20 °C) and good durability (300 cycles under 100% strain). Consequently, the anti-freezing ion-enhanced hydrogel will meet the needs of flexible sensors designed for intelligent robots, health monitoring, etc., which have to work in cold regions or extreme climates.

Nanosheet-hydrogel composites: from preparation and fundamental properties to their promising applications

Hydrogels are an important class of soft materials with elastic and intelligent properties. Nevertheless, these traditional hydrogels usually possess poor mechanical properties and limited functions, which greatly restrict their further applications. With the rapid development of nanotechnology, there have been significant advances in the design and fabrication of functional nanocomposite hydrogels with unique properties and functions. Among various materials, nanosheets with planar topography, large specific surface areas, and versatile physicochemical properties have attracted intense research interest. Herein, this review summarises the synthesis mechanisms, fundamental properties, and promising applications of nanosheet-incorporated hydrogels. In particular, how the nanosheet structure is applied to improve the overall performance of the hydrogel in each application is emphasized. Additionally, the current challenges and prospects are briefly discussed in this area. We expect that the combination of nanosheets and hydrogels can attract more researchers' interest and bring new opportunities in the future.

Ultra-Stretchable and Fast Self-Healing Ionic Hydrogel in Cryogenic Environments for Artificial Nerve Fiber

Self-healing materials behave with irreplaceable advantages in biomimetic intelligent robots (BIR) for avoiding or reducing safety hazards and economic losses from accidental damage during service. However, the self-healing ability is unreservedly lost and even becomes rigid and fragile in the cryogenic environment where BIR are precisely needed. Here, the authors report a versatile ionic hydrogel with fast self-healing ability, ultra-stretchability, and stable conductivity, even at -80 °C. The hydrogel is systematically optimized to improve a hydrogen-bonded network nanostructure, coordinated achieving a quick self-healing ability within 10 min, large deformation tolerance of over 7000%, superior conductivity of 11.76 S cm^-1 and anti-freezing ability, which is difficult to obtain simultaneously. Such a hydrogel provides new opportunities for artificial electronic devices in harsh environments. As a prospective application, they fabricate an artificial nerve fiber by mimicking the structure and functions of the myelinated axon, exhibiting the property of fast and potential-gated signal transmission. This artificial nerve fiber is integrated into a robot for demonstrating a real-time high fidelity and high throughput information interaction under big deformation and cryogenic temperature. The hydrogel and bionic device will bring pioneering functions for robots and open a broad application scenario in extreme conditions.

Flexible organohydrogel ionic skin with Ultra-Low temperature freezing resistance and Ultra-Durable moisture retention

HYPOTHESIS

One prevailing method to construct excellent temperature tolerance/long-lasting moisture hydrogels is to couple the original hydrogel networks with freezing-tolerant/moisture retaining agents, including ionic liquids, inorganic salts, zwitterionic osmolytes, and polyhydric alcohols. Among them, organohydrogels have shed new light on the development of ionic skins with long-term usability and stable sensing performance at subzero temperatures due to their long-lasting water retention and anti-freezing capability.

EXPERIMENTS

We report a dual network organohydrogel by doping conductive ZnSO₄ into the double network hydrogel of polyvinyl alcohol-polyacrylamide (PVA-PAM) with subsequent immersing in a mixed solvent of ethylene glycol (EG) and H₂O. The anti-freezing and moisture retaining abilities of the PVA/PAM/Zn/EG (PPZE) organohydrogel were studied and the sensing performances of the PPZE organohydrogel-based ionic skin were investigated.

FINDINGS

The organohydrogel exhibits a high conductivity (0.44 S m^-1), excellent fatigue resistance and exceptional moisture retaining ability with more than 99.3% of the initial weight retention after 31 days storage at ambient temperature. Importantly, the PPZE organohydrogel-based ionic skin shows an ultra-low temperature anti-freezing ability and remains flexibility and sensing capability with a high sensitivity (signal response time ∼ 0.23 s) even at -50 °C. The PPZE organohydrogel demonstrates a tremendous potential in artificial skin and health monitoring.

Dually cross-linked single network poly(ionic liquid)/ionic liquid ionogels for a flexible strain-humidity bimodal sensor

Gel electrolytes have aroused extensive interest for diverse flexible electronics due to their high ionic conductivity and inherent stretchability. However, gel electrolytes still face challenges in terms of mechanical properties, fatigue resistance, and environmental adaptation, which severely limit the practical application of gel-based electronics. In this paper, we have synthesized a novel polymerizable ionic liquid [SBMA][AA] by mixing zwitterionic sulfobetaine methacrylate with acrylic acid. Then a dually cross-linked single network poly(ionic liquid)/ionic liquid (DCSN PIL/IL) ionogel was prepared by a simple one-step photopolymerization of the [SBMA][AA] in another IL 1-ethyl-3-methylimidazolium dicyanoamide ([EmIm][DCA]). The synergistic effect between covalent crosslinking and dynamic physical crosslinking points endows the ionogel with good mechanical properties as well as outstanding fatigue resistance. Gratifyingly, the entrapment of [EmIm][DCA] in the ionogel matrix yields excellent environmental adaptability and high ionic conductivity. Meanwhile, the DCSN PIL/IL ionogel also exhibited strong adhesive capacity due to the abundance of carboxyl and sulphonic acid groups. The outstanding electromechanical properties make the DCSN PIL/IL ionogel a perfect candidate for strain sensors to monitor diverse human body activities, such as the movement of the thumb knuckle and handwriting. Interestingly, the DCSN PIL/IL ionogel also displayed high responsiveness to humidity. Therefore, it is believed that this DCSN PIL/IL ionogel offers a broad prospect in flexible strain-humidity bimodal sensors.

Effect of the swelling degree on the non-isothermal dehydration kinetics of a poly(acrylic acid)-g-gelatine hydrogel

The kinetics of non-isothermal dehydration of a poly(acrylic acid)-g-gelatine hydrogel swollen to different swelling degrees is investigated. The thermogravimetric curves are recorded at different heating rates in the interval from 5 K mol^-1 to 20 K mol^-1 within the temperature range from ambient temperature to 480 K. It is found that all kinetics curves can be described using the Weibull function. Based on the suggested kinetics model, the values of the specific rates are calculated and the values of apparent activation energies are established. Distribution functions of activation energies are obtained. The changes found in the values of Weibull function parameters, dependences of the specific rate on temperature, and apparent activation energies on temperature and the dehydration degree, as well as different activation energy distributions, are explained using the fluctuation model of a hydrogel, as a dynamically disordered system that goes through changes during the dehydration process. The presented results can have both fundamental and practical significance in the fields where the application is based on the ability of the hydrogel to conserve and slowly release water.

Investigating the relationship between the mechanical properties of plasma polymer-like thin films and their glass transition temperature

This work aims at understanding the influence of the substrate temperature (T_s) on the viscoelastic properties of propanethiol plasma polymer films (PPFs). By means of state-of-the-art AFM characterization-based techniques including peak force quantitative nanomechanical mapping (PFQNM), nano dynamic mechanical analysis (nDMA) and "scratch" experiments, it has been demonstrated that the mechanical behaviour of PPFs is dramatically affected by the thermal conditions of the substrate. Indeed, the material behaves from a high viscous liquid (i.e. viscosity ∼ 10⁶ Pa s) to a viscoelastic solid (loss modulus ∼ 1.17 GPa, storage modulus ∼ 1.61 GPa) and finally to an elastic solid (loss modulus ∼ 1.95 GPa, storage modulus ∼ 8.51 GPa) when increasing T_s from 10 to 45 °C. This behaviour is ascribed to an increase in the surface glass transition temperature of the polymeric network. The latter has been correlated with the chemical composition through the presence of unbound molecules acting as plasticizers and the cross-linking density of the layers. In a second step, this knowledge is exploited for the fabrication of a nanopattern by generating surface instabilities in the propanethiol PPF/Al bilayer system.

Stretchable multifunctional hydrogels for sensing electronics with effective EMI shielding properties

Hydrogel-based soft and stretchable materials with skin/tissue-like mechanical properties provide new avenues for the design and fabrication of wearable sensors. However, synthesizing multifunctional hydrogels that simultaneously possess excellent mechanical, electrical and electromagnetic interference (EMI) shielding effectiveness is still a great challenge. In this work, the freeze-casting method is employed to fabricate a multifunctional hydrogel by filling Fe₃O₄ clusters into poly(3,4-ethylenedioxythiophene)-poly(styrene sulfonic acid) (PEDOT:PSS) and polyvinyl alcohol (PVA) composite aqueous solution. The hydrogel possesses superior electrical and mechanical properties as well as great electromagnetic wave shielding properties. Benefiting from the high stretchability (∼904.5%) and fast sensing performance (response time ∼9 ms and self-recovery time ∼12 ms within the strain range ∼100%), the monitoring of human activities and manipulation of a remote-controlled toy car using the hydrogel-based stretchable strain sensors are successfully demonstrated. In addition, a great EMI shielding effectiveness with more than 46 dB in the frequencies of 8-12.5 GHz can be obtained, which provides an alternative strategy for designing next-generation EMI shielding materials. These results indicate that the multifunctional hydrogels can be used as flexible and stretchable sensing electronics requiring effective EMI shielding.

A facile route to dual-crosslinking polymeric hydrogels with enhanced mechanical property

Polymeric hydrogels with excellent biocompatibility, high hydrophilicity, and water-holding capacity have attracted considerable concerns in widely fields. However, most hydrogels exhibit poor mechanical property, which largely limited their applications. Herein, a novel dual-crosslinking polymeric hydrogel crosslinked by covalent bonds and metal coordination interactions between Fe3+ and –COO- was fabricated through accessible method. The metal coordination interactions within the hydrogel were established through dipping in the FeCl3 solution to reinforce the backbones of the hydrogel. The obtained polymeric hydrogel exhibits enhanced tensile strength (∼4.92 MPa), stiffness (∼6.168 MPa), and toughness (∼2.835 MJ m−3).

Super Stretchable and Compressible Hydrogels Inspired by Hook-and-Loop Fasteners

Inspired by hook-and-loop fasteners, we designed a hydrogel network containing α-zirconium phosphate (ZrP) two-dimensional nanosheets with a high density of surface hydroxyl groups serving as nanopatches with numerous "hooks," while polymer chains with plentiful amine functional groups serve as "loops." Our multiscale molecular simulations confirm that both the high density of hydroxyl groups on nanosheets and the large number of amine functional groups on polymer chains are essential to achieve reversible interactions at the molecular scale, functioning as nano hook-and-loop fasteners to dissipate energy. As a result, the synthesized hydrogel possesses superior stretchability (>2100% strain), resilience to compression (>90% strain), and durability. Remarkably, the hydrogel can sustain >5000 cycles of compression with torsion in a solution mimicking synovial fluid, thus promising for potential biomedical applications such as artificial articular cartilage. This hook-and-loop model can be adopted and generalized to design a wide range of multifunctional materials with exceptional mechanical properties.

Shape-Stable Hydrated Salts/Polyacrylamide Phase-Change Organohydrogels for Smart Temperature Management

Flexible and environmentally friendly phase-change materials (PCMs) with appropriate phase transition temperatures display great potential in the regulation of environmental temperature. Here, we synthesized a series of room-temperature-use phase-change organohydrogels (PCOHs) comprising phase-change hydrated salts (disodium phosphate dodecahydrate, DPDH) and polyacrylamide (PAM) glycerol hydrogels through a facile photoinitiated one-step in situ polymerization procedure. Incorporating the environmentally friendly cost-effective DPDH hydrated salts PCMs into antidrying three-dimensional (3D) networks of the PAM organohydrogel can overcome the solid rigidity and melting leakage to achieve flexibility for wearable temperature management devices. The microstructures and physical interactions among the components of the PCOHs were characterized by scanning electron microscopy (SEM), Fourier transform infrared (FTIR), and X-ray diffraction (XRD), which demonstrate that the DPDH were uniformly loaded in the networks of the PAM. Phase-change storage and thermal properties of the PCOHs were characterized by differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA), and the PCOHs show high energy transition efficiency and shape stability during the long-term storage and thermal cycling. Dynamic rheology and compression tests demonstrate that PCOHs can withstand a certain stress and display flexibility performance even above the melting temperature of DPDH. We also described the smart temperature management capability and the potential application of the PCOHs. This investigation offers a facile method to construct a skin-friendly flexible phase-change glycerol hydrogel and provides an alternative to the traditional melt impregnation or microencapsulation method to prepare phase-change energy storage composites.

Boron nitride-based nanocomposite hydrogels: preparation, properties and applications

Hexagonal boron nitride (h-BN) nanostructures are well-known for their good chemical stability, thermal conductivity and high elastic modulus. BN can be used as a filler in hydrogels to significantly improve their mechanical and thermal properties, to reinforce their biocompatibility and to provide self-healing capacity. Moreover, in contrast with their carbon equivalents, BN nanocomposites are transparent and electrically insulating. Herein, we present an overview of BN-based nanocomposite hydrogels. First, the properties of h-BN are described, as well as common exfoliation and functionalization techniques employed to obtain BN nanosheets. Then, methods for preparing BN-nanocomposite hydrogels are explained, followed by a specific overview of the relationship between the composition and structure of the nanocomposites and the functional properties. Finally, the main properties of these materials are discussed in view of the thermal, mechanical, and self-healing properties, along with the potential applications in tissue engineering, thermal management, drug delivery and water treatment.

A novel hydrogel with self-healing property and bactericidal activity

In this study, we have designed and synthesized a novel poly (4 - vinyl benzene boronic acid - co - N - vinyl pyrrolidone - co - 1 - vinyl - 3 - butylimidazolium bromide) hydrogel (VNV hydrogel) dressing with good self-healing properties and bactericidal activity. The gelation and self-healing of this hydrogel are mainly achieved by the formation of a dynamic B-O-B bond between the polymer chains, which is fractured by external forces and subsequently reformed. This self-healing mechanism is studied in detail through the molecular design of the hydrogel. The introduction of hydrophilic chemical groups can effectively improve the porous structures, water absorption and molecular migration. These properties have a positive effect on improving self-healing properties of dynamic crosslinked hydrogels. Furthermore, this VNV hydrogel dressing displays good antibacterial activity against E. coli, S. aureus, and C. albicans. The application of VNV hydrogel dressing on rat wound surface can effectively accelerate wound healing. These results indicate that this novel VNV hydrogel dressing with good self-healing properties and bactericidal activity has potential applications in wound dressings.

Biomimetic anti-freezing polymeric hydrogels: keeping soft-wet materials active in cold environments

As one of the most outstanding materials, the analysis of the structure and function of hydrogels has been extensively carried out to tailor and adapt them to various fields of application. The high water content, which is beneficial for plenty of applications in the biomedical setting, prevents the adoption of hydrogels in flexible electronics and sensors in real life applications, because hydrogels lose their excellent properties, including conductivity, transparency, flexibility, etc., upon freezing at sub-zero temperatures. Therefore, depressing the liquid-solid phase transition temperature is a powerful means to expand the application scope of hydrogels, and will benefit the chemical engineering and materials science communities. This review summarizes the recent research progress of anti-freezing hydrogels. At first, approaches for the generation of anti-freezing (hydro)gels are introduced and their anti-freezing mechanisms and performances are briefly discussed. These approaches are either based on addition of salts, alcohols (cryoprotectants and organohydrogels), and ionic liquids (ionogels), modification of the polymer network or a combination of several techniques. Then, a concise overview of applications leveraged by the widened temperature resistance is provided and future research areas and developments are envisaged.

Biomimetic Boroxine-Based Multifunctional Thermosets via One-Pot Synthesis

Boroxine-based thermosets with remarkable mechanical tunability, self-healing ability, recyclability, and adhesive strength are of significant importance in various applications. However, complex multistep reactions are often required to prepare such thermosets. Herein, a facile one-pot approach to synthesize boroxine-based malleable thermosets is proposed. Random copolymers with pendant boronic acid groups were synthesized from alkenyl monomers containing boronic acids [4-vinylphenylboronic acid (4-VPBA), 3-vinylphenylboronic acid, or 3-acrylamidophenylboronic acid] and octadecanoxy polyethylene glycol methacrylate. Then, the as-prepared copolymers were cured to form thermosets with boroxine bonds. The tensile strengths of the thermosets were tailored to range from 9.3 to 27.5 MPa by increasing the concentration of 4-VPBA. Moreover, because of the reversible nature of dynamic boroxine bonds (transformation between boroxines and boronic acids) induced by water, the thermosets exhibit remarkable self-healing efficiency (up to 99%), tunable mechanical properties, and excellent recyclability. Additionally, the thermosets also demonstrate superior adhesive strength (as high as 73.9 MPa) on different substrates.

Ultrastretchable, Tough, Antifreezing, and Conductive Cellulose Hydrogel for Wearable Strain Sensor

Conductive hydrogels have shown great potential in the field of flexible strain sensors. However, their application is greatly limited due to the low conductivity and poor mechanical properties at subzero temperatures. Herein, an ultrastretchable, tough, antifreezing, and conductive cellulose hydrogel was fabricated by grafting acrylonitrile and acrylamide copolymers onto the cellulose chains in the presence of zinc chloride using ceric ammonium nitrate as the initiator. The resulting hydrogel exhibited ultrastretchability (1730%), excellent tensile strength (160 kPa), high elasticity (90%), good toughness (1074.7 kJ/m³), and fatigue resistance property due to the existence of dipole-dipole and multiple hydrogen-bonding interactions on the hydrogel network. In addition, the introduced zinc chloride endowed the cellulose-based hydrogel with remarkable electric conductivity (1.54 S/m) and excellent antifreezing performance (-33 °C). Finally, the hydrogel showed high sensitivity and stability to monitor human activities. In summary, this work presented a facile strategy to construct conductive hydrogel with excellent antifreezing and mechanical properties simultaneously, which showed great potential for wearable strain sensors.

Poly(2-hydroxyethyl methacrylate)/β-cyclodextrin-hyaluronan contact lens with tear protein adsorption resistance and sustained drug delivery for ophthalmic diseases

A series of poly(2-hydroxyethyl methacrylate) (pHEMA) hydrogels containing cross-linked β-cyclodextrin-hyaluronan (β-CD-crHA), with tear protein adsorption resistance and sustained drug delivery, were developed as contact lens materials for eye diseases. β-CD-HA was synthesized from aminated β-CD and HA and then crosslinked within pHEMA hydrogel using polyethylenimine as a crosslinker. The synthesized β-CD-HA was characterized by ¹H NMR analysis, and β-CD-crHA immobilized in pHEMA hydrogel was confirmed by FT-IR, SEM, and AFM analyses. The incorporation of β-CD-crHA significantly improved the surface hydrophilicity, water uptake ability, oxygen permeability, and flexibility of pHEMA hydrogel, but did not compromise light transmission. pHEMA/β-CD-crHA hydrogels not only decreased the tear protein adsorption because of the electrostatically mutual repulsion and the improved hydrophilicity, leading to the reduced adhesion of Staphylococcus aureus on the hydrogel surface, but also enhanced the encapsulation capacity and the sustainable delivery of diclofenac due to the formation of inclusion complexes between β-CD and drugs. All the hydrogels were nontoxic to 3T3 mouse fibroblasts by in vitro cell viability analysis. Among these hydrogels with different β-CD-crHA contents, pHEMA/β-CD-crHA₁₀ hydrogel showed the lowest water contact angle of 52 °, the highest water content of 65%, the largest Dk value of 36.4 barrer, and the optimal modulus of 1.8 MPa, as well as a good light transmission of over 90%. The in vivo conjunctivitis treatment of rabbits for 72 h indicated that drug-loaded pHEMA/β-CD-crHA₁₀ hydrogel presented a better therapeutic effect than both one dose administration of drug solution per day and drug-loaded pHEMA hydrogel. Thus, pHEMA/β-CD-crHA₁₀ hydrogel is a promising contact lens material for ophthalmic diseases. STATEMENT OF SIGNIFICANCE: Topical eye drops are currently the most popular treatment for ophthalmic diseases, but frequent dosing is necessary to acquire the desirable clinical effect at the expense of systemic side-effects. Drug-loaded contact lenses, as an alternative of eye drops, possess many good performances and show potential applications. However, the sustained drug delivery and the tear protein adsorption resistance are still challenging for contact lenses. Hence, we developed a novel pHEMA/β-CD-crHA hydrogel by incorporating β-CD-crHA crosslinked network into pHEMA hydrogel. Besides the improvements in surface hydrophilicity, water uptake ability, oxygen permeability, and flexibility, pHEMA/β-CD-crHA hydrogel also reduced the adsorption of tear proteins and the adhesion of Staphylococcus aureus, enhanced the drug encapsulation, and prolonged the drug delivery, with better effect in the conjunctivitis treatment of rabbits. Thus, pHEMA/β-CD-crHA hydrogel is a potential contact lens material for treating ophthalmic diseases.

Transparency and AIE tunable supramolecular polymer hydrogel acts as TEA-HCl vapor controlled smart optical material

Stimuli-responsive optical materials attract lots of attention due to their broad applications. Herein, a novel smart stimuli-responsive supramolecular polymer was successfully constructed using a simple tripodal quaternary ammonium-based gelator (TH). The TH self-assembles into a supramolecular polymer hydrogel (TH-G) and shows aggregation-induced emission (AIE) properties. Interestingly, the transparency and fluorescence of the TH-G xerogel film (TH-GF) could be reversibly regulated by use of triethylamine (TEA) and hydrochloric acid (HCl) vapor. When alternately fumed with TEA and HCl vapor, the optical transmittance of the TH-GF was changed from 8.9% to 92.7%. Meanwhile, the fluorescence of the TH-G shows an "ON/OFF" switch. The reversible switching of the transparency and the fluorescence of the TH-GF is attributed to the assembly and disassembly of the supramolecular polymer TH-G. Based on these stimuli-response properties, the TH-GF could act as an optical material and shows potential applications as smart windows or fluorescent display material controlled by TEA and HCl vapor.

Transparent and Flexible Electronics Assembled with Metallic Nanowire-Layered Nondrying Glycerogel

There has been increasing demand for transparent and mechanically durable electrical conductors for their uses in wearable electronic devices. It is common to layer metallic nanowires on transparent but stiff poly(dimethylsiloxane) (PDMS) or stretchable but opaque Ecoflex-based substrates. Here, we hypothesized that layering metallic nanowires on a stretchable and hygroscopic gel would allow us to assemble a transparent, stretchable, and durable conductor. The hygroscopic property of the gel was attained by partially replacing water in the preformed polyacrylamide hydrogel with glycerol. The resulting gel, denoted as a glycerogel, could remain hydrated for over 6 months in air by taking up water molecules from the air. The glycerogel was tailored to be stretchable up to 8 times its original length by tuning the amount of the cross-linker and acrylamide. The resulting glycerogel allowed for deposition of wavy silver nanowires using the prestrain method up to 400% prestrain, without causing kinks and interfacial cracks often found with nanowires layered onto PDMS. With a prestrain of 100%, the resulting nanowire-gel conductor exhibited optical transparency (85%) and electrical conductivity (17.1 ohm/sq) even after 5000 cycles of deformation. The results of this study would broadly be useful to improve the performance of the next generation of flexible electronic devices.

Dual-cross-linked dynamic hydrogels with cucurbit[8]uril and imine linkages

The strategy of dual cross-linking was investigated by enhancing the performance of dynamic hydrogels. To this end, phenylalanine modified ε-polylysine was synthesized and employed as the polymer backbone of hydrogels. The phenylalanine moieties and amine groups of the polymer could be cross-linked with cucurbit[8]uril (CB[8]) and the dialdehyde cross-linker, respectively. Single CB[8] linkage with fast dynamics led to an increase in the viscosity of the polymer solution, and single imine linkage with slow dynamics led to the formation of weak and brittle hydrogels. However, the two linkages were combined together to form a dual-cross-linked hydrogel and the performance of the hydrogel could be well enhanced. Compared with the single imine cross-linked hydrogel, the dual-cross-linked hydrogel demonstrated a higher mechanical strength, better extensibility and faster self-healing rate. It is anticipated that this line of research could provide a useful method to enhance the performance of dynamic hydrogels.