Shear‐Thinning Supramolecular Hydrogels with Secondary Autonomous Covalent Crosslinking to Modulate Viscoelastic Properties In Vivo

Clinical percutaneous delivery of synthetically engineered hydrogels remains limited due to challenges posed by crosslinking kinetics—too fast leads to delivery failure, too slow limits material retention. To overcome this challenge, supramolecular assembly is exploited to localize hydrogels at the injection site and introduce subsequent covalent crosslinking to control final material properties. Supramolecular gels are designed through the separate pendant modifications of hyaluronic acid (HA) by the guest–host pair cyclodextrin and adamantane, enabling shear‐thinning injection and high target site retention (>98%). Secondary covalent crosslinking occurs via addition of thiols and Michael‐acceptors (i.e., methacrylates, acrylates, vinyl sulfones) on HA and increases hydrogel moduli (E = 25.0 ± 4.5 kPa) and stability (>3.5 fold in vivo at 28 d). Application of the dual‐crosslinking hydrogel to a myocardial infarct model shows improved outcomes relative to untreated and supramolecular hydrogel alone controls, demonstrating its potential in a range of applications where the precise delivery of hydrogels with tunable properties is desired.     

Thermogelling,ABC Triblock Copolymer Platform for Resorbable Hydrogels with Tunable,Degradation‐Mediated Drug Release

Clinical application of injectable, thermoresponsive hydrogels is hindered by lack of degradability and controlled drug release. To overcome these challenges, a family of thermoresponsive, ABC triblock polymer‐based hydrogels has been engineered to degrade and release drug cargo through either oxidative or hydrolytic/enzymatic mechanisms dictated by the “A” block composition. Three ABC triblock copolymers are synthesized with varying “A” blocks, including oxidation‐sensitive poly(propylene sulfide), slow hydrolytically/enzymatically degradable poly(ε‐caprolactone), and fast hydrolytically/enzymatically degradable poly(d ,l ‐lactide‐co‐glycolide), forming the respective formulations PPS₁₃₅‐b‐PDMA₁₅₂‐b‐PNIPAAM₂₂₅ (PDN), PCL₈₅‐b‐PDMA₁₅₀‐b‐PNIPAAM₁₅₀ (CDN), and PLGA₆₀‐b‐PDMA₁₄₈‐b‐PNIPAAM₁₅₂ (LGDN). For all three polymers, hydrophilic poly(N,N‐dimethylacrylamide) and thermally responsive poly(N‐isopropylacrylamide) comprise the “B” and “C” blocks, respectively. These copolymers form micelles in aqueous solutions at ambient temperature that can be preloaded with small molecule drugs. These solutions quickly transition into hydrogels upon heating to 37 °C, forming a supra‐assembly of physically crosslinked, drug‐loaded micelles. PDN hydrogels are selectively degraded under oxidative conditions while CDN and LGDN hydrogels are inert to oxidation but show differential rates of hydrolytic/enzymatic decomposition. All three hydrogels are cytocompatible in vitro and in vivo, and drug‐loaded hydrogels demonstrate differential release kinetics in vivo corresponding with their specific degradation mechanism. These collective data highlight the potential cell and drug delivery use of this tunable class of ABC triblock polymer thermogels.     

Multicolored Nanocolloidal Hydrogel Inks

Nanocolloidal gels are emerging as a promising class of materials with applications as inks in 2D and 3D printing. Polymer nanoparticles (NPs) offer many advantages as potential building blocks of nanocolloidal gels, due to the ability to control NP dimensions, charge, surface chemistry, and functionality; however, their applications as inks in printing are yet to be explored. Here, functional nanocolloidal hydrogels formed by percolating oppositely charged latex NPs with different dimensions and charge densities are reported. The shear-thinning and self-healing properties of the nanocolloidal gels and the mechanical properties of the resulting printed films are examined. NP functionality is achieved by covalently labeling them with different fluorescent dyes that emit at two distinct wavelengths. Using these NPs, a facile route for 3D printing of multicolored fluorescence patterns is shown, with each color being visualized under a specific, well-defined excitation wavelength.     

Bionic soft crystalline lens materials for MEMs applications based on self-assembling amphiphilic block copolymer/nanoparticle hybrids

In this study, a biomimetic crystalline lens with properties that combine the softness of a hydrogel comparable to that of a human lens for adjustable focus and the property for image aberration correction with gradient refractive index (GRIN) was developed by the self-organization of an amphiphilic block copolymer blended with high refractive index titanium nanoparticles (TiO₂). The hydrogel lens was prepared by using a thermally responsive poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PPO-PEO-PPO) triblock copolymer (Poloxamer 407) with the lower-critical solution temperature (LCST) property that can be injectable into the eye capsule as a liquid below its LCST and solidifies as a soft gel above the LCST at the human body temperature. By chemical modification of the triblock copolymer with double bonds on its chain-ends (Poloxamer 407A), the soft lens network can be made by using UV crosslinking of the hydrogel. To further increase the refractive index (RI) of the hydrogel lens network and to match its RI to that of the human lens (=1.41), highly visible-light transparent titanium dioxide (TiO₂) nanoparticles were introduced into the hydrogel lens network. To create a biomimetic GRIN lens as in the human’s eyes, an electric field method was also used to induce an axial diffusion of TiO₂ nanoparticles from the center of the lens where TiO₂ nanoparticles were first injected to the edge. The above method demonstrates the potential to use the hydrogel/nanoparticle hybrid as an injectable replacement for a soft optical lens system with an adjustable focus for future MEMs application.     

Self‐Assembled Injectable Nanocomposite Hydrogels Stabilized by Bisphosphonate‐Magnesium (Mg2+) Coordination Regulates the Differentiation of Encapsulated Stem Cells via Dual Crosslinking

Nanocomposite hydrogels consist of a polymer matrix embedded with nanoparticles (NPs), which provide the hydrogels with unique bioactivities and mechanical properties. Incorporation of NPs via in situ precipitation in the polymer matrix further enhances these desirable hydrogel properties. However, the noncytocompatible pH, osmolality, and lengthy duration typically required for such in situ precipitation strategies preclude cell encapsulation in the resultant hydrogels. Bisphosphonate (BP) exhibits a variety of specific bioactivities and excellent binding affinity to multivalent cations such as magnesium ions (Mg²⁺). Here, the preparation of nanocomposite hydrogels via self‐assembly driven by bisphosphonate‐Mg²⁺ coordination is described. Upon mixing solutions of polymer bearing BPs, BP monomer (Ac‐BP), and Mg²⁺, this effective and dynamic coordination leads to the rapid self‐assembly of Ac‐BP‐Mg NPs which function as multivalent crosslinkers stabilize the resultant hydrogel structure at physiological pH. The obtained nanocomposite hydrogels are self‐healing and exhibit improved mechanical properties compared to hydrogels prepared by blending prefabricated NPs. Importantly, the hydrogels in this study allow the encapsulation of cells and subsequent injection without compromising the viability of seeded cells. Furthermore, the acrylate groups on the surface of Ac‐BP‐Mg NPs enable facile temporal control over the stiffness and crosslinking density of hydrogels via UV‐induced secondary crosslinking, and it is found that the delayed introduction of this secondary crosslinking enhances cell spreading and osteogenesis.     

Growth‐Factor Free Multicomponent Nanocomposite Hydrogels That Stimulate Bone Formation

Synthetic osteo‐promoting materials that are able to stimulate and accelerate bone formation without the addition of exogenous cells or growth factors represent a major opportunity for an aging world population. A co‐assembling system that integrates hyaluronic acid tyramine ( HA‐Tyr ), bioactive peptide amphiphiles ( GHK‐Cu²⁺ ), and Laponite ( Lap ) to engineer hydrogels with physical, mechanical, and biomolecular signals that can be tuned to enhance bone regeneration is reported. The central design element of the multicomponent hydrogels is the integration of self‐assembly and enzyme‐mediated oxidative coupling to optimize structure and mechanical properties in combination with the incorporation of an osteo‐ and angio‐promoting segments to facilitate signaling. Spectroscopic techniques are used to confirm the interplay of orthogonal covalent and supramolecular interactions in multicomponent hydrogel formation. Furthermore, physico‐mechanical characterizations reveal that the multicomponent hydrogels exhibit improved compressive strength, stress relaxation profile, low swelling ratio, and retarded enzymatic degradation compared to the single component hydrogels. Applicability is validated in vitro using human mesenchymal stem cells and human umbilical vein endothelial cells, and in vivo using a rabbit maxillary sinus floor reconstruction model. Animals treated with the HA‐Tyr‐HA‐Tyr‐GHK‐Cu²⁺ hydrogels exhibit significantly enhanced bone formation relative to controls including the commercially available Bio‐Oss.     

Biodegradable Polymer Crosslinker: Independent Control of Stiffness,Toughness, and Hydrogel Degradation Rate

Hydrogels are being increasingly studied for use in various biomedical applications including drug delivery and tissue engineering. The successful use of a hydrogel in these applications greatly relies on a refined control of the mechanical properties including stiffness, toughness, and the degradation rate. However, it is still challenging to control the hydrogel properties in an independent manner due to the interdependency between hydrogel properties. Here it is hypothesized that a biodegradable polymeric crosslinker would allow for decoupling of the dependency between the properties of various hydrogel materials. This hypothesis is examined using oxidized methacrylic alginate (OMA). The OMA is synthesized by partially oxidizing alginate to generate hydrolytically labile units and conjugating methacrylic groups. It is used to crosslink poly(ethylene glycol) methacrylate and poly(N‐hydroxymethyl acrylamide) to form three‐dimensional hydrogel systems. OMA significantly improves rigidity and toughness of both hydrogels as compared with a small molecule crosslinker, and also controls the degradation rate of hydrogels depending on the oxidation degree, without altering their initial mechanical properties. The protein‐release rate from a hydrogel and subsequent angiogenesis in vivo are thus regulated with the chemical structure of OMA. Overall, the results of this study suggests that the use of OMA as a crosslinker will allow the implantation of a hydrogel in tissue subject to an external mechanical loading with a desired protein‐release profile. The OMA synthesized in this study will be, therefore, highly useful to independently control the mechanical properties and degradation rate of a wide array of hydrogels.     

A Printable Photopolymerizable Thermosensitive p(HPMAm‐lactate)‐PEG Hydrogel for Tissue Engineering

Bioprinting is a new technology in regenerative medicine that allows the engineering of tissues by specific placement of cells in biomaterials. Importantly, the porosity and the relatively small dimensions of the fibers allow rapid diffusion of nutrients and metabolites. This technology requires the availability of hydrogels that ensure viability of encapsulated cells and have adequate mechanical properties for the preparation of structurally stable and well‐defined three‐dimensional constructs. The aim of this study is to evaluate the suitability of a biodegradable, photopolymerizable and thermosensitive A–B–A triblock copolymer hydrogel as a synthetic extracellular matrix for engineering tissues by means of three dimensional fiber deposition. The polymer is composed of poly(N‐(2‐hydroxypropyl)methacrylamide lactate) A‐blocks, partly derivatized with methacrylate groups, and hydrophilic poly(ethylene glycol) B‐blocks of a molecular weight of 10 kDa. Gels are obtained by thermal gelation and stabilized with additional chemical cross‐links by photopolymerization of the methacrylate groups coupled to the polymer. A power law dependence of the storage plateau modulus of the studied hydrogels on polymer concentration is observed for both thermally and chemically cross‐linked hydrogels. The hydrogels demonstrated mechanical characteristics similar to natural semi‐flexible polymers, including collagen. Moreover, the hydrogel shows suitable mechanical properties for bioprinting, allowing subsequent layer‐by‐layer deposition of gel fibers to form stable constructs up to at least 0.6 cm (height) with different patterns and strand spacing. The resulting constructs have reproducible vertical porosity and the ability to maintain separate localization of encapsulated fluorescent microspheres. Moreover, the constructs show an elastic modulus of 119 kPa (25 wt% polymer content) and a degradation time of approximately 190 days. Furthermore, high viability is observed for encapsulated chondrocytes after 1 and 3 days of culture. In summary, we conclude that the evaluated hydrogel is an interesting candidate for bioprinting applications.     

In Vivo Imaging of Composite Hydrogel Scaffold Degradation Using CEST MRI and Two‐Color NIR Imaging

Hydrogel scaffolding of stem cells is a promising strategy to overcome initial cell loss and manipulate cell function post‐transplantation. Matrix degradation is a requirement for downstream cell differentiation and functional tissue integration, which determines therapeutic outcome. Therefore, monitoring of hydrogel degradation is essential for scaffolded cell replacement therapies. It is shown here that chemical exchange saturation transfer magnetic resonance imaging (CEST MRI) can be used as a label‐free imaging platform for monitoring the degradation of crosslinked hydrogels containing gelatin (Gel) and hyaluronic acid (HA), of which the stiffness can be fine‐tuned by varying the ratio of the Gel:HA. By labeling Gel and HA with two different near‐infrared (NIR) dyes having distinct emission frequencies, it is shown here that the HA signal remains stable for 42 days, while the Gel signal gradually decreases to <25% of its initial value at this time point. Both imaging modalities are in excellent agreement for both the time course and relative value of CEST MRI and NIR signals (R² = 0.94). These findings support the further use of CEST MRI for monitoring biodegradation and optimizing of gelatin‐containing hydrogels in a label‐free manner.     

Skin‐Inspired Antibacterial Conductive Hydrogels for Epidermal Sensors and Diabetic Foot Wound Dressings

Recently, artificial intelligence research has driven the development of stretchable and flexible electronic systems. Conductive hydrogels are a class of soft electronic materials that have emerging applications in wearable and implantable biomedical devices. However, current conductive hydrogels possess fundamental limitations in terms of their antibacterial performance and a mechanical mismatch with human tissues, which severely limits their applications in biological interfaces. Here, inspired by animal skin, a conductive hydrogel is fabricated from a supramolecular assembly of polydopamine decorated silver nanoparticles (PDA@Ag NPs), polyaniline, and polyvinyl alcohol, namely PDA@Ag NPs/CPHs. The resultant hydrogel has many desirable features, such as tunable mechanical and electrochemical properties, eye‐catching processability, good self‐healing ability as well as repeatable adhesiveness. Remarkably, PDA@Ag NPs/CPHs exhibit broad antibacterial activity against Gram‐negative and Gram‐positive bacteria. The potential application of this versatile hydrogel is demonstrated by monitoring large‐scale movements of the human body in real time. In addition, PDA@Ag NPs/CPHs have a significant therapeutic effect on diabetic foot wounds by promoting angiogenesis, accelerating collagen deposition, inhibiting bacterial growth, and controlling wound infection. To the best of the authors' knowledge, this is the first time that conductive hydrogels with antibacterial ability are developed for use as epidermal sensors and diabetic foot wound dressing.     

Actuation of Three-Dimensional-Printed Nanocolloidal Hydrogel with Structural Anisotropy

Polymer hydrogels exhibit actuation properties that result in reversible shape transformations and have promising applications in soft robotics, drug delivery systems, sensors, and microfluidic devices. Actuation occurs due to differential hydrogel swelling and is generally achieved by modulating hydrogel composition. Here a different approach to hydrogel actuation that originates solely from its structural anisotropy is reported. For 3D-printed single-layer hydrogels formed by cellulose nanocrystals (CNCs) and gelatin methacryloyl it is shown that shear-induced orientation of CNCs results in anisotropic mechanical and swelling properties of the hydrogel. Upon swelling in water, planar hydrogels acquire multiple complex 3D shapes that are achieved by i) varying CNC orientation with respect to the shape on the hydrogel sheet and ii) patterning the hydrogel with the regions of shear-mediated and random CNC orientation. This study shows the capability to generate multiple shapes from the same hydrogel actuator based on the degree of its structural anisotropy. In addition, it introduces a biocompatible nanocolloidal ink with shear-thinning and self-healing properties for additive manufacturing of hydrogel actuators.     

A Zn‐Doped CuO Nanocomposite Shows Enhanced Antibiofilm and Antibacterial Activities Against Streptococcus Mutans Compared to Nanosized CuO

Zinc‐doped copper oxide and copper oxide nanoparticles (NPs) are synthesized and deposited on artificial teeth by sonic irradiation, and the ability of these coatings to restrict biofilm formation by Streptococcus mutans is examined. The CuO and Zn:CuO NP‐coated teeth show significant reductions in biofilm formation of 70% and 88%, respectively, compared to uncoated teeth. The mechanism of the Zn:CuO nanoparticles is investigated, revealing that the nanoparticles attach to and penetrate the bacteria and generate intracellular reactive oxygen species (ROS) that enhance lipid peroxidation and cause cell death. Conversely, the CuO or ZnO NPs do not show this behavior and could not generate intracellular ROS. These results highlight the superior efficacy of Zn:CuO nanocomposites over CuO and ZnO NPs and the role of ROS in their antimicrobial effect.     

Touchable Electrochemical Hydrogel Sensor for Detection of Reactive Oxygen Species-induced Cellular Senescence in Articular Chondrocytes

In this study, a reactive oxygen species (ROS)-responsive hydrogel sensor (PD/MnO₂ hydrogel) is developed that can efficiently detect senescent cells. Using immature murine articular chondrocytes with serial passages, the sensor can identify small interfering RNA (siRNA) knockdown of peroxisome proliferator-activated receptor-alpha (PPARα) based on the concentration of ROS in cells, simultaneously maintaining its balance via scavenging activity to prevent cartilage degradation in osteoarthritis (OA). The hydrogel sensor exhibits a change in electronic properties, with a distinct resistance from 201.9 kΩ for P0 to 362.9 kΩ for P3, and fluorescence off/on performance with an increase in passaging time. In vitro investigation using PPARα-specific siRNA reveals a correlation between pressure sensitivity and senescent activity, wherein an elevation in observed signal occurred (41.5%). In vivo analysis reveals significant decrease in degradation of the cartilage of both young, 3 months old aged, 18 months old, and PPARα^−/− mice compared to PPARα^+/+ mice based on safranin O stains. The expression level of interleukin-1β is reduced in the cartilage of aged PPARα^−/− mice after implantation with hydrogel, indicating the potential of PD/MnO₂ hydrogel as a therapeutic modality against OA.     

Conductive “Smart” Hybrid Hydrogels with PNIPAM and Nanostructured Conductive Polymers

Stimuli‐responsive hydrogels with decent electrical properties are a promising class of polymeric materials for a range of technological applications, such as electrical, electrochemical, and biomedical devices. In this paper, thermally responsive and conductive hybrid hydrogels are synthesized by in situ formation of continuous network of conductive polymer hydrogels crosslinked by phytic acid in poly(N‐isopropylacrylamide) matrix. The interpenetrating binary network structure provides the hybrid hydrogels with continuous transporting path for electrons, highly porous microstructure, strong interactions between two hydrogel networks, thus endowing the hybrid hydrogels with a unique combination of high electrical conductivity (up to 0.8 S m^?1), high thermoresponsive sensitivity (significant volume change within several seconds), and greatly enhanced mechanical properties. This work demonstrates that the architecture of the filling phase in the hydrogel matrix and design of hybrid hydrogel structure play an important role in determining the performance of the resulting hybrid material. The attractive performance of these hybrid hydrogels is further demonstrated by the developed switcher device which suggests potential applications in stimuli‐responsive electronic devices.     

Poly(N‐isopropylacrylamide)‐Clay Nanocomposite Hydrogels with Responsive Bending Property as Temperature‐Controlled Manipulators

Novel poly(N‐isopropylacrylamide)‐clay (PNIPAM‐clay) nanocomposite (NC) hydrogels with both excellent responsive bending and elastic properties are developed as temperature‐controlled manipulators. The PNIPAM‐clay NC structure provides the hydrogel with excellent mechanical property, and the thermoresponsive bending property of the PNIPAM‐clay NC hydrogel is achieved by designing an asymmetrical distribution of nanoclays across the hydrogel thickness. The hydrogel is simply fabricated by a two‐step photo polymerization. The thermoresponsive bending property of the PNIPAM‐clay NC hydrogel is resulted from the unequal forces generated by the thermoinduced asynchronous shrinkage of hydrogel layers with different clay contents. The thermoresponsive bending direction and degree of the PNIPAM‐clay NC hydrogel can be adjusted by controlling the thickness ratio of the hydrogel layers with different clay contents. The prepared PNIPAM‐clay NC hydrogels exhibit rapid, reversible, and repeatable thermoresponsive bending/unbending characteristics upon heating and cooling. The proposed PNIPAM‐clay NC hydrogels with excellent responsive bending property are demonstrated as temperature‐controlled manipulators for various applications including encapsulation, capture, and transportation of targeted objects. They are highly attractive material candidates for stimuli‐responsive “smart” soft robots in myriad fields such as manipulators, grippers, and cantilever sensors.     

Flexible MXene-Based Hydrogel Enables Wearable Human–Computer Interaction for Intelligent Underwater Communication and Sensing Rescue

Conductive hydrogels have recently attracted extensive attention in the field of smart wearable electronics. Despite the current versatility of conductive hydrogels, the balance between mechanical properties (tensile properties, strength, and toughness) and electrical properties (electrical conductivity, sensitivity, and stability) still faces great challenges. Herein, a simplified method for constructing hydrophobic association hydrogels with excellent mechanical and electrical properties is proposed. The prepared conductive hydrogels exhibit high tensile properties (≈1224%), high linearity in the whole-strain–range (R² = 0.999), and a wide strain sensing range (2700%). The conductive hydrogel can realize more than 1000 cycles of sensing under 500% tensile strain. As an application demonstration, an underwater communication device is assembled in combination with polydimethylsiloxane/Triton X-100 film coating, which successfully transmits underwater signals and provides warning of potential hazards. This study provides a new research method for developing underwater equipment with excellent mechanical properties and sensing properties.     

Dual Physically Cross-Linked Hydrogels Incorporating Hydrophobic Interactions with Promising Repairability and Ultrahigh Elongation

Novel dual physically cross-linked (DPC) hydrogels with great tensile strength, ultrahigh elongation, and promising repairability are designed by introducing cellulose nanocrystal (CNC) or hydrophobized CNC (CNC-C8) into polymers physically cross-linked by hydrophobic forces. C18 alkyl chain is grafted to N-[3-(dimethylamino)propyl]methacrylamide (DMAPMA) for hydrophobic monomer (DMAPMA-C18), and C8 to CNC surface for hydrophobic CNC (CNC-C8). CNC-C8 (or CNC) DPC hydrogels are synthesized, with monomers N,N-dimethylacrylamide (DMAc) and DMAPMA-C18 polymerized to form the first network physically cross-linked by hydrophobic interactions, on which the secondary cross-linking points are formed by hydrophobic interactions between CNC-C8 and DMAPMA-C18, electrostatic interactions between CNC-C8 (or CNC) and DMAPMA, as well as hydrogen bonding between CNC-C8 (or CNC) and DMAc. Compared with optimum CNC DPC hydrogels of the highest tensile strength (238 ± 8 kPa), the optimum CNC-C8 DPC hydrogel with 0.0675 w/v% DMAPMA-C18 and 0.4 w/v% CNC-C8 possesses stronger tensile strength of 331 ± 32 kPa and excellent elongation of 4268% ± 1446% as well, demonstrating the enhanced mechanical property of the hydrogel by introduced hydrophobic interactions. In addition, such DPC hydrogel can be facilely repaired with tetrahydrofuran (THF) on the cut surfaces while retaining good tensile stress and elongation behaviors.     

An Intelligent Transdermal Formulation of ALA-Loaded Copolymer Thermogel with Spontaneous Asymmetry by Using Temperature-Induced Sol–Gel Transition and Gel–Sol (Suspension) Transition on Different Sides

Aqueous solutions of some amphiphilic block copolymers undergo a sol–gel transition upon heating and are thus called thermogels. In the thermogel family, some systems also exhibit a gel–sol (suspension) transition at higher temperatures following the sol–gel transition, which is usually ignored in biomedical applications. Herein, for the first time, a case is reported employing both the sol–gel transition and the gel–sol (suspension) transition, which is found in the development of a transdermal hydrogel formulation containing 5-aminolevulinic acid for photodynamic therapy (PDT) of skin disease. Two poly(d ,l -lactide-co-glycolide)-b-poly(ethylene glycol)-b-poly(d ,l -lactide-co-glycolide) triblock copolymers of different block lengths are synthesized. The transition temperatures of the formulation can be easily adjusted to meet the condition of sol–gel transition temperature (T_gel) < room temperature (T_air) < gel–sol (suspension) temperature (T_{sol (suspension)}) < body temperature (T_body) via changing the blending ratio. Therefore, after applying to skin, formulation of spontaneous asymmetry with a hydrogel outside and a sol (suspension) inside can avoid free flowing and achieve rapid release to ensure an efficient PDT. This study demonstrates such a concept via characterizations of the “block blend” biomaterials and drug release profiles, and also via cell experiments, in vitro permeation, and in vivo transdermal delivery studies.     

Tough and Self‐Recoverable Thin Hydrogel Membranes for Biological Applications

Tough and self‐recoverable hydrogel membranes with micrometer‐scale thickness are promising for biomedical applications, which, however, rarely be realized due to the intrinsic brittleness of hydrogels. In this work, for the first time, by combing noncovalent DN strategy and spin‐coating method, we successfully fabricated thin (thickness: 5–100 µm), yet tough (work of extension at fracture: 10⁵–10⁷ J m^?3) and 100% self‐recoverable hydrogel membranes with high water content (62–97 wt%) in large size (≈100 cm²). Amphiphilic triblock copolymers, which form physical gels by self‐assembly, were used for the first network. Linear polymers that physically associate with the hydrophilic midblocks of the first network, were chosen for the second network. The inter‐network associations serve as reversible sacrificial bonds that impart toughness and self‐recovery properties on the hydrogel membranes. The excellent mechanical properties of these obtained tough and thin gel membranes are comparable, or even superior to many biological membranes. The in vitro and in vivo tests show that these hydrogel membranes are biocompatible, and postoperative nonadhesive to neighboring organs. The excellent mechanical and biocompatible properties make these thin hydrogel membranes potentially suitable for use as biological or postoperative antiadhesive membranes.     

Stimuli-Responsive Peptide Self-Assembly to Construct Hydrogels with Actuation and Shape Memory Behaviors

Hydrogel actuators, capable of generating reversible deformation in response to external stimulus, are widely considered as new emerging intelligent materials for applications in soft robots, smart sensors, artificial muscles, and so on. Peptide self-assembly is widely applied in the construction of intelligent hydrogel materials due to their excellent stimulus response. However, hydrogel actuators based on peptide self-assembly are rarely reported and explored. In this study, a pH-responsive peptide (MA-FIID) is designed and introduced into a poly(N-isopropyl acrylamide) backbone (PNIPAM) to construct bilayer and heterogeneous hydrogel actuators based on the assembly and disassembly of peptide molecules under different pH conditions. These peptide-containing hydrogel actuators can perform controllable bending, bucking, and complex deformation under pH stimulation. Meanwhile, the Hofmeister effect of PNIPAM hydrogels endows these peptide-containing hydrogels with enhanced mechanical strength, ionic stimulus response (CaCl₂), and excellent shape-memory property. This work broadens the application of supramolecular self-assembly in the construction of intelligent hydrogels, and also provides new inspirations for peptide self-assembly to construct smart materials.