A double-network hydrogel for the dynamic compression of the lumbar nerve root

Current animal models of nerve root compression due to lumbar disc herniation only assess the mechanical compression of nerve roots and the inflammatory response. Moreover, the pressure applied in these models is static, meaning that the nerve root cannot be dynamically compressed. This is very different from the pathogenesis of lumbar disc herniation. In this study, a chitosan/polyacrylamide double-network hydrogel was prepared by a simple two-step method. The swelling ratio of the double-network hydrogel increased with prolonged time, reaching 140. The compressive strength and compressive modulus of the hydrogel reached 53.6 and 0.34 MPa, respectively. Scanning electron microscopy revealed the hydrogel's crosslinked structure with many interconnecting pores. An MTT assay demonstrated that the number of viable cells in contact with the hydrogel extracts did not significantly change relative to the control surface. Thus, the hydrogel had good biocompatibility. Finally, the double-network hydrogel was used to compress the L4 nerve root of male sand rats to simulate lumbar disc herniation nerve root compression. The hydrogel remained in its original position after compression, and swelled with increasing time. Edema appeared around the nerve root and disappeared 3 weeks after operation. This chitosan/polyacrylamide double-network hydrogel has potential as a new implant material for animal models of lumbar nerve root compression. All animal experiments were approved by the Animal Ethics Committee of Neurosurgical Institute of Beijing, Capital Medical University, China(approval No. 201601006) on July 29, 2016.

An Endotenon Sheath-Inspired Double-Network Binder Enables Superior Cycling Performance of Silicon Electrodes

Silicon(Si)has been regarded as an alternative anode material to traditional graphite owing to its higher theoretical capacity(4200 vs.372 m Ah g;).However,Si anodes suffer from the inherent volume expansion and unstable solid electrolyte interphase,thus experiencing fast capacity decay,which hinders their commercial application.To address this,herein,an endotenon sheathinspired water-soluble double-network binder(DNB)is presented for resolving the bottleneck of Si anodes.The as-developed binder shows excellent adhesion,high mechanical properties,and a considerable self-healing capability mainly benefited by its supramolecular hybrid network.Apart from these advantages,this binder also induces a Li;N/Li F-rich solid electrolyte interface layer,contributing to a superior cycle stability of Si electrodes.As expected,the DNB can achieve mechanically more stable Si electrodes than traditional polyacrylic acid and pectin binders.As a result,DNB delivers superior electrochemical performance ofSi/Li half cells and Li Ni;Co;Mn;O;/Si full cells,even with a high loading of Si electrode,to traditional polyacrylic acid and pectin binders.The bioinspired binder design provides a promising route to achieve long-life Si anode-assembled lithium batteries.

Highly conductive and tough double-network hydrogels for smart electronics

Development and understanding of highly mechanically robust and electronically conducting hydrogels are extremely important for ever-increasing energy-based applications.Conventional mixing/blending of conductive additives with hydrophilic polymer network prevents both high mechanical strength and electronic conductivity to be presented in polymer hydrogels.Here,we proposed a double-network(DN)engineering strategy to fabricate PVA/PPy DN hydrogels,consisting of a conductive PPy-PA network via in-situ ultrafast gelation and a tough PVA network via a subsequent freezing/thawing process.The resultant PVA/PPy hydrogels exhibited superior mechanical and electrochemical properties,including electrical conductivity of~6.8 S/m,mechanical strength of~0.39 MPa,and elastic moduli of~0.1 MPa.Upon further transformation of PVA/PPy hydrogels into supercapacitors,they demonstrated a high capacitance of~280.7 F/g and a cycle life of 2000 galvanostatic charge/discharge cycles with over 94.3%capacity retention at the current density of 2 mA/cm2 and even subzero temperatures of−20℃.Such enhanced mechanical performance and electronic conductivity of hydrogels are mainly stemmed from a synergistic combination of continuous electrically conductive PPy-PA network and the two interpenetrating DN structure.This in-situ gelation strategy is applicable to the integration of ionic-/electrical-conductive materials into DN hydrogels for smart-soft electronics,beyond the most commonly used PEDOT:PSS-based hydrogels.

A double-network porous hydrogel based on high internal phase emulsions as a vehicle for potassium sucrose octasulfate delivery accelerates diabetic wound healing

Diabetic wounds are a difficult medical challenge.Excessive secretion of matrix metalloproteinase-9(MMP-9)in diabetic wounds further degrades the extracellular matrix and growth factors and causes severe vascular damage,which seriously hinders diabetic wound healing.To solve these issues,a double-network porous hydrogel composed of poly(methyl methacrylate-co-acrylamide)(p(MMA-co-AM))and polyvinyl alcohol(PVA)was constructed by the high internal phase emulsion(HIPE)technique for the delivery of potassium sucrose octasulfate(PSO),a drug that can inhibit MMPs,increase angiogenesis and improve microcirculation.The hydrogel possessed a typical polyHIPE hierarchical microstructure with interconnected porous morphologies,high porosity,high specific surface area,excellent mechanical properties and suitable swelling properties.Meanwhile,the p(MMA-co-AM)/PVA@PSO hydrogel showed high drug-loading performance and effective PSO release.In addition,both in vitro and in vivo studies showed that the p(MMA-co-AM)/PVA@PSO hydrogel had good biocompatibility and significantly accelerated diabetic wound healing by inhibiting excessive MMP-9 in diabetic wounds,increasing growth factor secretion,improving vascularization,increasing collagen deposition and promoting re-epithelialization.Therefore,this study provided a reliable therapeutic strategy for diabetic wound healing,some theoretical basis and new insights for the rational design and preparation of wound hydrogel dressings with high porosity,high drug-loading performance and excellent mechanical properties.

Highly stretchable double-network gel electrolytes integrated with textile electrodes for wearable thermo-electrochemical cells

Thermo-electrochemical cells(TECs)provide a new potential for self-powered devices by converting heat energy into electricity.However,challenges still remain in the fabrication of flexible and tough gel electrolytes and their compat-ibility with redox actives;otherwise,contact problems exist between electrolytes and electrodes during stretching or twisting.Here,a novel robust and neutral hydrogel with outstanding stretchability was developed via double-network of crosslinked carboxymethyl chitosan and polyacrylamide,which accommodated both n-type(Fe^(2+)/Fe^(3+))and p-type([Fe(CN)_(6)]^(3-)/[Fe(CN)_(6)]^(4-))redox couples and maintained stretchability(>300%)and recoverability(95%compression).Moreover,poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate)textile elec-trodes with porous structure are integrated into gel electrolytes that avoid contact issues and effectively boost the P_(max) of n-and p-type thermocell by 76%and 26%,respectively.The optimized thermocell exhibits a quick current density response and is continually fully operational under deformations,which satisfies the working conditions of wearable devices.Multiple thermocells(four pairs)are effectively connected in alternating single n-and p-type cells in series and out-putted nearly 74.3 mV atΔT=10℃.The wearable device is manufactured into a soft-pack thermocells to successfully harvest human body heat and illuminate an LED,demonstrating the potential of the actual application of the thermocell devices.

Nanosilver anchored alginate/poly(acrylic acid/acrylamide) double-network hydrogel composites for efficient catalytic degradation of organic dyes

A novel alginate/poly(acrylic acid/acrylamide)double-network hydrogel composite with silver nanoparticles was successfully fabricated using the sol–gel method.The presence of carboxyl and amide groups in the network structure provided abundant active sites for complexing silver ions,facilitating the in situ reduction and confinement of silver nanoparticles.In batch experiments,the optimal silver loading was 20%,and 5 mmol·L^(–1) of p-nitrophenol was completely degraded in 113 s with a rate constant value of 4.057×10^(−2) s^(–1).In the tap water system and simulated seawater system,the degradation time of p-nitrophenol at the same concentration was 261 and 276 s,respectively,with a conversion rate above 99%.In the fixed-bed experiment,the conversion rate remained above 74%after 3 h at a flowing rate of 7 mL·min^(–1).After 8 cycling tests,the conversion rate remained at 98.7%.Moreover,the catalyst exhibited outstanding performance in the degradation experiment of four typical organic dyes.

An Environment‑Tolerant Ion‑Conducting Double‑Network Composite Hydrogel for High‑Performance Flexible Electronic Devices

High-performance ion-conducting hydrogels(ICHs)are vital for developing flexible electronic devices.However,the robustness and ion-conducting behavior of ICHs deteriorate at extreme tempera-tures,hampering their use in soft electronics.To resolve these issues,a method involving freeze–thawing and ionizing radiation technology is reported herein for synthesizing a novel double-network(DN)ICH based on a poly(ionic liquid)/MXene/poly(vinyl alcohol)(PMP DN ICH)system.The well-designed ICH exhibits outstanding ionic conductivity(63.89 mS cm^(-1) at 25℃),excellent temperature resistance(-60–80℃),prolonged stability(30 d at ambient temperature),high oxidation resist-ance,remarkable antibacterial activity,decent mechanical performance,and adhesion.Additionally,the ICH performs effectively in a flexible wireless strain sensor,thermal sensor,all-solid-state supercapacitor,and single-electrode triboelectric nanogenerator,thereby highlighting its viability in constructing soft electronic devices.The highly integrated gel structure endows these flexible electronic devices with stable,reliable signal output performance.In particular,the all-solid-state supercapacitor containing the PMP DN ICH electrolyte exhibits a high areal specific capacitance of 253.38 mF cm^(-2)(current density,1 mA cm^(-2))and excellent environmental adaptability.This study paves the way for the design and fabrication of high-performance mul-tifunctional/flexible ICHs for wearable sensing,energy-storage,and energy-harvesting applications.

Regulating Mechanical Properties of Polymer-Supramolecular Double-Network Hydrogel by Supramolecular Self-assembling Structures

Main observation and conclusion Polymer-supramolecular double-network hydrogels(PS-DN hydrogels)often show much improved recovery rates than conventional double-network hydrogels because of the fast self-assembling properties,making them attractive candidates for tissue engineering and flexible electronics.However,as the supramolecular network is dynamic and susceptible to break under low strains,the overall mechanical properties of PS-DN hydrogels are still limited.Here,we report the mechanical properties for PS-DN hydrogels can be significantly improved by tuning the supramolecular network structures.A single amino acid change of the self-assembling peptide can tune the assembled structures from nanofiber to nanoribbon.Such a microscopic structural change can greatly increase the Young's modulus(107.4 kPa),fracture stress(0.48 MPa),and toughness(0.38 MJ·m^(–3))of the PS-DN hydrogels.Moreover,the structural change also leads to slightly faster recovery rates(<1 s).We propose that such dramatically different mechanical properties can be understood by the impact of individual peptide rupture events on the overall network connectivity in the two scenarios.Our study may provide new inspirations for combining high mechanical strength and fast recovery in double network hydrogels by tuning the supramolecular network structures.

Mechanical and Tribological Study of PVA–pMPDSAH Double-Network Hydrogel Prepared by Ultraviolet Irradiation and Freeze–Thaw Methods for Bionic Articular Cartilage

Hydrogel has been widely used in the research of bionic articular cartilage due to their similarity in structure and functional properties to natural articular cartilage.In this research,polyvinyl alcohol and betaine monomer were used as raw materials to prepare a high-strength double-network hydrogel by a combination of ultraviolet(UV)irradiation and freeze–thaw methods.The structure of samples was characterized by Fourier transform infrared spectroscopy and X-ray diff raction,and the morphology of the samples was characterized by scanning electron microscope and three-dimensional white light interferometer.In addition,we also studied the swelling ratio,water content,mechanical properties and tribological properties of the samples.We found that the addition of betaine monomer and the UV irradiation time had a positive eff ect on the mechanical properties and tribological properties of the samples.

Tetradic double-network physical crosslinking hydrogels with synergistic high stretchable, self-healing, adhesive, and strain-sensitive properties

Herein,we demonstrate a tetradic double-network physical cross-linking hydrogel comprising of gelatin,polyacrylic acid,tannic acid,and aluminum chloride as wearable hydrogel sensors.Based on the coordination bonds,hydrogen bonds,and chain entanglements of the two networks,the acquired hydrogel possesses excellent tensile properties,self-healing performance,and adhesiveness to many substrates.Mechanical properties can be tuned with fracture strain ranging from 900 to 2200%and tensile strength ranging from 24 to 216 kPa,respectively.Besides,the hydrogel also exhibits good strain-sensitivity when monitoring the motions of humans,such as bending of fingers,bending of elbows.Hence,we can believe that the GATA hydrogel has numerous applications in soft robots,intelligent wearable devices,and human health supervision.

A Microstructural Damage Model toward Simulating the Mullins Effect in Double-Network Hydrogels

The damage models based on the eight-chain model and the affine full-chain network model are not adequate to describe the damage behaviors in double-network(DN)hydrogels.To overcome this limitation,we propose a combined chain stretch model with new damage flow rules.It is demonstrated that the new proposed micro-chain stretch is a reduced form of the complete representation for the transversely isotropic tensor function.As a result,the damage models based on the eight-chain model and the affine model are incorporated as special cases.The effects of chain affineness and network entangling are simultaneously involved in the new model,while only one of these two effects can be characterized in either the eight-chain model or the affine model.It is further shown that the new model can effectively capture the Mullins features of the DN hydrogels and achieve better agreement with the experimental data than the affine model and the eight-chain model.

Extrusion bioprinting of elastin-containing bioactive double-network tough hydrogels for complex elastic tissue regeneration

Despite recent advances in extrusion bioprinting of cell-laden hydrogels,using nat-urally derived bioinks to biofabricate complex elastic tissues with both satisfying biological functionalities and superior mechanical properties is hitherto an unmet challenge.Here,we address this challenge with precisely designed biological tough hydrogel bioinks featuring a double-network structure.The tough hydrogels con-sisted of energy-dissipative dynamically crosslinked glycosaminoglycan hyaluronic acid(o-nitrobenzyl-grafted hyaluronic acid)and elastin through Schiff’s base reac-tion,and free-radically polymerized gelatin methacryloyl.The incorporation of elastin further improved the elasticity,stretchability(∼170%strain),and tough-ness(∼45 kJ m-3)of the hydrogels due to the random coiling structure.We used this novel class of hydrogel bioinks to bioprint several complex elastic tissues with good shape retention.Furthermore,in vitro and in vivo experiments also demon-strated that the existence of elastin in the biocompatible bioinks facilitated improved cell behaviors and biological functions of bioprinted tissues,such as cell spreading and phenotype maintenance as well as tissue regeneration.The results confirmed the potential of the elastin-containing tough hydrogel bioinks for bioprinting of 3D complex elastic tissues with biological functionalities,which mayfind widespread applications in elastic tissue regeneration.

A Review on the Mullins Effect in Tough Elastomers and Gels

Tough elastomers and gels have garnered broad research interest due to their wide-ranging potential applications.However,during the loading and unloading cycles,a clear stress softening behavior can be observed in many material systems,which is also named as the Mullins effect.In this work,we aim to provide a complete review of the Mullins effect in soft yet tough materials,specifically focusing on nanocomposite gels,double-network hydrogels,and multi-network elastomers.We first revisit the experimental observations for these soft materials.We then discuss the recent developments of constitutive models,emphasizing novel developments in the damage mechanisms or network representations.Some phenomenological models will also be briefly introduced.Particular attention is then placed on the anisotropic and multiaxial modeling aspects.It is demonstrated that most of the existing models fail to accurately predict the multiaxial data,posing a significant challenge for developing future anisotropic models tailored for tough gels and elastomers.

Recent advances in polysaccharide-based hydrogels for synthesis and applications

Hydrogels are three-dimensional(3D)crosslinked hydrophilic polymer networks that have garnered tremendous interests in many fields,including water treatment,energy storage,and regenerative medicine.However,conventional synthetic polymer hydrogels have poor biocompatibility.In this context,polysaccharides,a class of renewable natural materials with biocompatible and biodegradable properties,have been utilized as building blocks to yield polysaccharide-based hydrogels through physical and/or chemical crosslinking of polysaccharides via a variety of monomers or ions.These polysaccharide-derived hydrogels exhibit peculiar physicochemical properties and excellent mechanical properties due to their unique structures and abundant functional groups.This review focuses on recent advances in synthesis and applications of polysaccharide-based hydrogels by capitalizing on a set of biocompatible and biodegradable polysaccharides(i.e.,cellulose,alginate,chitosan,and cyclodextrins[CDs]).First,we introduce the design and synthesis principles for crafting polysaccharide-based hydrogels.Second,polysaccharidebased hydrogels that are interconnected via various crosslinking strategies(e.g.,physical crosslinking,chemical crosslinking,and double networking)are summarized.In particular,the introduction of noncovalent and/or dynamic covalent interactions imparts polysaccharide-based hydrogels with a myriad of intriguing performances(e.g.,stimuli–response and self-recovery).Third,the diverse applications of polysaccharide-based hydrogels in self-healing,sensory,supercapacitor,battery,drug delivery,wound healing,tissues engineering,and bioimaging fields are discussed.Finally,the perspectives of polysaccharide-based hydrogels that promote their future design to enable new functions and applications are outlined.