Improving physical properties of poly(vinyl alcohol)/montmorillonite nanocomposite hydrogels via the Hofmeister effect

Hydrogel is a kind of three-dimensional crosslinked polymer material with high moisture content.However,due to the network defects of polymer gels,traditional hydrogels are usually brittle and fragile,which limits their practical applications.Herein,we present a Hofmeister effect-aided facile strategy to prepare high-performance poly(vinyl alcohol)/montmorillonite nanocomposite hydrogels.Layered montmorillonite nanosheets can not only serve as crosslinking agents to enhance the mechanical properties of the hydrogel but also promote the ion conduction.More importantly,based on the Hofmeister effect,the presence of(NH_(4))_(2)SO_(4)can endow nanocomposite hydrogels with excellent mechanical properties by affecting PVA chains'aggregation state and crystallinity.As a result,the as-prepared nanocomposite hydrogels possess unique physical properties,including robust mechanical and electrical properties.The as-prepared hydrogels can be further assembled into a high-performance flexible sensor,which can sensitively detect large-scale and small-scale human activities.The simple design concept of this work is believed to provide a new prospect for developing robust nanocomposite hydrogels and flexible devices in the future.

Thermal-responsive Photonic Crystals based on Physically Cross-linked Inverse Opal Nanocomposite Hydrogels

A thermal-responsive photonic crystal material was fabricated by forming an inverse opal nanocomposite hydrogel of poly(N-isopropylacrylamide)(IONHPNIPAm)within the interstitial space of a polystyrene photonic crystal template.In IONHPNIPAm,PNIPAm were physically cross-linked with two kinds of nanoparticles(carbon dots and laponite clays).The integration of carbon dots and laponite clays for physical crosslinking endowed IONHPNIPAm sufficient strength and self-healing property.IONHPNIPAm films can be completely peeled from the substrates to be utilized as an independent photonic crystal material.The structural color and optical diffraction of the IONHPNIPAm exhibits a rapid reversible change in response to external thermal stimuli due to its physical cross-linking feature.Moreover,the IONHPNIPAm shows clear fluorescence due to the introduction of carbon dots,which enables a convenient way for chemical detection(such as the detection of silver ions).This stimuli-responsive photonic crystal materials based on physically cross-linked inverse opal nanocomposite hydrogels with fast response and good mechanical stability are promising for applications in the fields of smart optical detectors,thermal-responsive sensors and chemical detectors.

Advanced Nanocomposite Arabic Gum Polyacrylic Acid Hydrogels for Flexible Supercapacitors

In this work,the fabrication and characterization of the nanocomposite hydrogel,as a solid electrode in electro-chemical cell and gel electrolyte material using Indium titanium oxide/polyethylene terephthalate(ITO/PET)flex-ible substrate for double-layer supercapacitors have been reported.The nanocomposite hydrogel composed of Arabic gum(AG),Acrylic acid(AA),reduced graphene oxide(RGO),and silver nanoparticles(AgNPs)was fab-ricated via a physical cross-linked polymerization reaction,in which the ascorbic acid was used as a reducing agent to generate AgNPs and to convert Graphene oxide(GO)to RGO during the polymerization reaction.The morphology and structural characteristics of nanocomposite hydrogel were investigated using atomic force microscopy(AFM),scanning electron microscope(SEM),Fourier transfer infrared(FTIR),and X-rayfluores-cence(XRF).Additionally,the effect of RGO and AgNPs on hydrogel stability was assessed through Thermogra-vimetric analysis(TGA)and differential scanning calorimetry(DSC),while its mechanical properties were studied using the nanoindentation test.Electrochemical impedance spectroscopy(EIS),and cyclic voltammetry(CV)were also conducted to study the electrochemical properties of the prepared hydrogel.The effects of AgNPs,RGO,and water content were all considered in the study of supercapacitor performance.The microstructural tests showed that the nanocomposite hydrogel has a relatively high swelling rate,which has a crucial effect on the capa-citance.Furthermore,the effects of increasing AgNP concentration and water content in the hydrogel matrix showed a significant improvement in its electrochemical performance,compared with that for Arabic gum poly acrylic acid(AGPAA)hydrogel itself,were the specific capacitance exhibited a significant enhancement,convert-ing from a low value to a substantially higher capacitance value.Moreover,when the nanocomposite hydrogel was used as the working electrode in an electrochemical cell with a hydrochloric acid(HCl)electrolyte solution,it exhibited good electrode performance.Additionally,using(ITO/PET)as aflexible substrate for nanocomposite hydrogel shows an improvement in their suitability for supercapacitor applications.Therefore,it is suggested that the fabricated hydrogel supercapacitor has potential applications in thefield of renewable and clean energy harvesting.

Flexible healable electromagnetic-interference-shielding bioelastichydrogel nanocomposite for machine learning-assisted highlysensitive sensing bioelectrode

The prosperous evolution of conductive hydrogel-based skin sensors is attract-ing tremendous attention nowadays.Nevertheless,it remains a great challenge to simultaneously integrate excellent mechanical strength,desirable electrical conduc-tivity,admirable sensing performance,and brilliant healability in hydrogel-based skin sensors for high-performance diagnostic healthcare sensing and wearable human-machine interface,as well as robust photothermal performance for promptly intelligent photothermal therapy followed by the medical diagnosis and superior electromagnetic interference(EMI)shielding performance for personal protec-tion.Herein,aflexible healable MXene hydrogel-based skin sensor is prepared through a delicate combination of MXene(Ti_(3)C_(2)T_(x))nanosheets network with the polymeric network.The as-prepared skin sensor is featured with significantly enhanced mechanical,conducting,and sensing performances,along with robust self-healability,good biocompatibility,and reliable injectability,enabling ultrasensitive human motion monitoring and teeny electrophysiological signals sensing.As a fron-tier technology in artificial intelligence,machine learning can facilitate to efficiently and precisely identify the electromyography signals produced by various human motions(such as variablefinger gestures)with up to 99.5%accuracy,affirming the reliability of the machine learning-assisted gesture identification with great poten-tial in smart personalized healthcare and human-machine interaction.Moreover,the MXene hydrogel-based skin sensor displays prominent EMI shielding performance,demonstrating the great promise of effective personal protection.

Bisphosphonate-based nanocomposite hydrogels for biomedical applications

Nanocomposite hydrogels consist of polymeric network embedded with functional nanoparticles or nanostructures,which not only contribute to the enhanced mechanical properties but also exhibit the bioactivities for regulating cell behavior.Bisphosphonates(BPs)are capable of coordinating with various metal ions and modulating bone homeostasis.Thanks to the inherent dynamic properties of metal–ligand coordination bonds,BPbased nanocomposite hydrogels possess tunable mechanical properties,highly dynamic structures,and the capability to mediate controlled release of encapsulated therapeutic agents,thereby making them highly versatile for various biomedical applications.This review presents the comprehensive overview of recent developments in BP-based nanocomposite hydrogels with an emphasis on the properties of embedded nanoparticles(NPs)and interactions between hydrogel network and NPs.Furthermore,various challenges in the biomedical applications of these hydrogels are discussed to provide an outlook of potential clinical translation.

Nanocomposite hydrogels based on carbon dots and polymers

Nanocomposite hydrogels based on carbon dots(CDs)and polymers have emerged as new materials with integrated properties of individual components,leading to their important applications in the field of soft nanomaterials.This perspective highlights recent advances in the development of nanocomposite hydrogels from CDs and polymers.We review the preparation methods of nanocomposite hydrogels based on CDs and polymers,and emerging applications of these nanocomposite hydrogels such as environmental remediation,energy storage,sensing,drug delivery and bioimaging.We conclude with the discussion of new research directions in the development of new type of nanocomposite hydrogels based on CDs and polymers.

Transparent h-BN/polyacrylamide nanocomposite hydrogels with enhanced mechanical properties

In this study, a facile way has been proposed to prepare transparent, tough and flexible polyacrylamide （PAM） hydrogels which is composed of a dually crosslinked single network by chemical crosslinking of N,N＇-methylenebisacrylamide （BIS） and physical crosslinking of hydrophilic hexagonal boron nitride （h- BN） nanosheets. The resulting h-BN/PAM nanocomposite hydrogels are highly transparent, and exhibit significantly enhanced mechanical properties compared to the dark （GO）/PAM nanocomposite hydrogels or chemical crosslinking PAM hydrogels. Thus it opens up new opportunities for developing next- generation transparent, tough and flexible hydrogels that hold great promise in such important applications as light responsive soft robot and liquid microlenses.

A fast on-demand preparation of injectable self-healing nanocomposite hydrogels for efficient osteoinduction

Injectable hydrogels have been considered as promising materials for bone regeneration,but their osteoinduction and mechanical performance are yet to be improved.In this study,a novel biocompatible injectable and self-healing nano hybrid hydrogel was on-demand prepared via a fast(within 30 s)and easy gelation approach by reversible Schiff base formed between-CH=O of oxidized sodium alginate(OSA)and-NH2 of glycol chitosan(GCS)mixed with calcium phosphate nanoparticles(CaP NPs).Its raw materials can be ready in large quantities by a simple synthesis process.The mechanical strength,degradation and swelling behavior of the hydrogel can be readily controlled by simply controlling the molar ratio of-CH=O and-NH2.This hydrogel exhibits pH responsiveness,good degradability and biocompatibility.The hydrogel used as the matrix for mesenchymal stem cells can significantly induce the proliferation,differentiation and osteoinduction in vitro.These results showed this novel hydrogel is an ideal candidate for applications in bone tissue regeneration and drug delivery.

Toughening Mechanism of Nanocomposite Physical Hydrogels Fabricated by a Single Gel Network with Dual Crosslinking-- The Roles of the Dual Crosslinking Points

A facile method to fabricate tough and highly stretchable polyacrylamide （PAM） nanocomposite physical hydrogel （NCP gel） was proposed. The hydrogels are dually crosslinked single network with the PAM grafted vinyl hybrid silica nanoparticles （VSNPs） as the analogous covalent crosslinking points and the reversible hydrogen bonds among the PAM chains as the physical crosslinking points. In order to further elucidate the toughening mechanism of the PAM NCP gel, especially to understand the role of the dual crosslinking points, the PAM hybrid hydrogels （H gels） and a series of poly（acrylamide-co-dimethylacrylamide） （P（AM-co-DMAA）） NCP gels were designed and fabricated. Their mechanical properties were compared with those of the PAM NCP gels. The PAM H gels are prepared by simply mixing the PAM chains with bare silica nanoparticles （SNPs）. Relative to the poor mechanical properties of the PAM H gel, the PAM NCP gel is remarkably tough and stretchable and also generates large number of micro-cracks to stop notch propagation, indicating the important role of PAM grafted VSNPs in toughening the NCP gel. In the P（AM-co-DMAA） NCP gels, the P（AM-co- DMAA） chains are grafted on VSNPs and the polydimethylacrylamide （PDMAA） only forms very weak hydrogen bonds between themselves. It is found that mechanical properties of the PAM NCP gel, such as the tensile strength and the elongation at break, are enhanced significantly, but those of the P（AM-co-DMAA） NCP gels decreased rapidly with decreasing AM content. This result reveals the role of the hydrogen bonds among the grafted polymer chains as the physical crosslinking points in toughening the NCP gel.

Tough superabsorbent poly(acrylic acid) nanocomposite physical hydrogels fabricated by a dually cross-linked single network strategy

In this work, we report a facile method for the preparation of tough and highly stretchable physical hydrogels by dual cross-linking composed of vinyl-hybrid silica nanoparticles（VSNPs） as multivalent covalent cross-linking and hydrogen bonding as physical cross-linking. Poly（acrylic acid） nanocomposite physical hydrogels（NCP gels） are obtained without adding any organic chemical cross-linkers. When the content of VSNPs is 0.7 wt%（relative to the monomer）, the NCP gels exhibit good mechanical properties（fracture strength = 370 k Pa, elongation at break = 2200%） and a high swelling capacity in both deionized water（2300 g/g） and saline（220 g/g）. Meanwhile, the NCP gels have good recovery ability.

Phase Transition Temperature Controllable Poly(acrylamide-co-acrylic acid) Nanocomposite Physical Hydrogels with High Strength

Poly（acrylamide-co-acrylic acid） nanocomposite physical （P（AAm-co-AAc）NCP） hydrogels have been prepared through the in situ free radical solution polymerization based on a ＂single network, dual cross-linkings＂ strategy. The P（AAm-co-AAc） NCP hydrogels are composed of nanobrushes of P（AAm-co-AAc） chains grafted on the surface of vinyl- hybrid silica nanoparticles （VSNPs）. In the hydrogel system, the VSNPs act as the ＂analogous chemical cross-linking points＂ once the hydrogen bonds formed between the P（AAm-co-AAc） chains of the nanobrushes, thus leading to the fabrication of high-strength P（AAm-co-AAc） NCP hydrogels. Compared with conventional thermosensitive P（AAm-co-AAc） hydrogels, the P（AAm-co-AAc） NCP hydrogels have a broader range of phase transition temperature, which can be adjusted by altering the monomer ratio, the VSNPs concentration, the addition of urea and N,N-dimethylacrylamide （DMAAm）. At the same time, the mechanical properties of the P（AAm-co-AAc） NCP hydrogels have been improved significantly by the introduction of VSNPs. Furthermore, both the phase transition and the tensile strength of the P（AAm-co-AAc） NCP hydrogels are largely influenced when Fe3＋ ions are introduced as the ionic crosslinkers into the hydrogel networks.

A multifunctional nanocomposite hydrogel with controllable release behavior enhances bone regeneration

Autologous and allogeneic bone grafts remain the gold standard for repairing bone defects.However,donor shortages and postoperative infections contribute to unsatisfactory treatment outcomes.Tissue engineering technology that utilizes biologically active composites to accelerate the healing and reconstruction of segmental bone defects has led to new ideas for in situ bone repair.Multifunctional nanocomposite hydrogels were constructed by covalently binding silver(Ag^(+))core-embedded mesoporous silica nanoparticles(Ag@MSN)to bone morphogenetic protein-2(BMP-2),which was encapsulated into silk fibroin methacryloyl(SilMA)and photo-crosslinked to form an Ag@MSN-BMP-2/SilMA hydrogel to preserve the biological activity of BMP-2 and slow its release.More importantly,multifunctional Ag^(+)-containing nanocomposite hydrogels showed antibacterial properties.These hydrogels possessed synergistic osteogenic and antibacterial effects to promote bone defect repair.Ag@MSN-BMP-2/SilMA exhibited good biocompatibility in vitro and in vivo owing to its interconnected porosity and improved hydrophilicity.Furthermore,the multifunctional nanocomposite hydrogel showed controllable sustained-release activity that promoted bone regeneration in repairing rat skull defects by inducing osteogenic differentiation and neovascularization.Overall,Ag@MSN-BMP-2/SilMA hydrogels enrich bone regeneration strategies and show great potential for bone regeneration.

Effect of nanoheat stimulation mediated by magnetic nanocomposite hydrogel on the osteogenic differentiation of mesenchymal stem cells

Hyperthermia has been considered as a promising healing treatment in bone regeneration. We designed a tissue engineering hydrogel based on magnetic nanoparticles to explore the characteristics of hyperthermia for osteogenic regeneration. This nanocomposite hydrogel was successfully fabricated by incorporating magnetic Fe_3O_4 nanoparticles into chitosan/polyethylene glycol(PEG) hydrogel, which showed excellent biocompatibility and were able to easily achieve increasing temperatures under an alternative magnetic field(AMF). With uniformly dispersed nanoparticles, the composite hydrogel resulted in high viability of mesenchymal stem cells(MSCs), and the elevated temperature contributed to the highest osteogenic differentiation ability compared with direct heat treatment applied under equal temperatures. Therefore, the nanoheat stimulation method using the magnetic nanocomposite hydrogel under an AMF may be considered as an alternative candidate in bone tissue engineering regenerative applications.

Characterization of a Multi-responsive Magnetic Graphene Oxide Nanocomposite Hydrogel and Its Application for DOX Delivery

Nanocomposite hydrogels are one of the most important types of biomaterials which can be used in many different applications such as drug delivery and tissue engineering.Incorporatio n of nano particles within a hydrogel matrix can provide unique characteristics like remote stimulate and improved mechanical strength.In this study,the synthesis of graphene oxide and graphene oxide nanocomposite hydrogel has been studied.Nanocomposite hydrogel was synthesized using carboxymethyl cellulose as a natural base,acrylic acid as a comonomer,graphene oxide as a filler,ammonium persulfate as an initiator,and iron nanoparticles as a crosslinking agent.The effect of reaction variables such as the iron nanoparticles,graphene oxide,ammonium persulfate,and acrylic acid were examined to achieve a hydrogel with maximum absorbency.Doxorubicin,an anti-cancer chemotherapy drug,was loaded into this hydrogel and its release behaviors were examined in the phosphate buffer solutions with different pH values.The structure of the graphene oxide and the optimized hydrogel were confirmed by Fourier-transform infrared spectroscopy,Raman spectroscopy,X-ray diffraction,scanning electron microscopy,and atomic force microscopy.

Hyaluronic acid methacrylate/laponite hydrogel loaded with BMP4 and maintaining its bioactivity for scar-free wound healing

Scar-free wound healing is a challenging process due to the excessive deposition of extracellular matrix and collagen.To overcome this issue,hydrogels with superior biochemical and mechanical properties have been used in combination with medicinal compounds as wound dressings.In this study,a novel composite hydrogel consisting of double-crosslinked photocurable hyaluronic acid methacrylate(HAMA)and Laponite(Lap)loaded with bioactive bone morphogenetic protein 4(BMP4)was developed and thoroughly characterized for its properties such as degradation,morphology,porosity,compression,skin adhesion and load release.The effect of the HAMA/Lap/BMP4 hydrogel was evaluated through both in vitro and in vivo experiments.In the in vivo rabbit ear-scar model,the HAMA/Lap/BMP4 hydrogel dressing was found to reduce scar-related expressions ofα-SAM and decrease the ratio of collagenΙ/III in wounded tissue.Additionally,histopathological examination indicated that the HAMA/Lap/BMP4 hydrogel-treated groups exhibited enhanced wound repair and increased levels of collagen maintenance compared to other standard groups,ultimately leading to scarless wound healing.Therefore,this sustained-release photocurable HAMA/Lap/BMP4 hydrogel offers a therapeutic approach for scar-free wound healing.

自愈合导电复合水凝胶用于监测人体运动和3D细胞培养

导电水凝胶已在多个领域崭露头角,因为它具备将外界压力和形变转化为电信号的能力,可实现对物理和化学刺激的灵敏感知.然而,在导电水凝胶的研发中,需要克服平衡导电性和机械强度的挑战.本项工作中,为了提高导电水凝胶的力学性能,我们采用了多重策略.首先,引入了木质素-丹宁酸(lignin-TA)颗粒作为物理交联剂,同时充分利用羟丙基纤维素分子的多羟基结构,促进水凝胶半互穿聚合物网络的形成.随后,通过利用Fe^(3+)离子和TA分子之间的静电力和金属配位相互作用,进一步增强了聚合物网络之间的键合强度,提高了水凝胶的导电性.最终,所制备的导电水凝胶以其独特的网络结构,成功融合了物理和化学键的特性,并展现出卓越的自粘附、自愈合能力、电机械性能和生物相容性.这使其成为一个可用于监测人体活动和细胞增殖的理想材料.

PDA-BPs integrated mussel-inspired multifunctional hydrogel coating on PPENK implants for anti-tumor therapy,antibacterial infection and bone regeneration

Currently,many cancer patients with bone defects are still threatened by tumor recurrence,postoperative bacterial infection,and massive bone loss.Many methods have been studied to endow bone implants with biocompatibility,but it is difficult to find an implant material that can simultaneously solve the problems of anticancer,antibacterial and bone promotion.Here,a multifunctional gelatin methacrylate/dopamine methacrylate adhesive hydrogel coating containing 2D black phosphorus(BP)nanoparticle protected by polydopamine(pBP)is prepared by photocrosslinking to modify the surface of poly(aryl ether nitrile ketone)containing phthalazinone(PPENK)implant.The multifunctional hydrogel coating works in conjunction with pBP,which can deliver drug through photothermal mediation and kill bacteria through photodynamic therapy at the initial phase followed by promotion of osteointegration.In this design,photothermal effect of pBP control the release of doxorubicin hydrochloride loaded via electrostatic attraction.Meanwhile,pBP can generate reactive oxygen species(ROS)to eliminate bacterial infection under 808 nm laser.In the slow degradation process,pBP not only effectively consumes excess ROS and avoid apoptosis induced by ROS in normal cells,but also degrade into PO43to promote osteogenesis.In summary,nanocomposite hydrogel coatings provide a promising strategy for treatment of cancer patients with bone defects.

Two-dimensional tungstate nanosheets for constructing novel photochromic hydrogel with ultrahigh flexibility

A hydrogel possessing interesting photochromic behaviors was developed by in situ ultraviolet(UV)irradiation-assisted polymerization of an aqueous solution of N-isopropylacrylamide monomer in the presence of cesium tungstate nanosheets.By this process,a hierarchical porous network structure was finely constructed while showing ultrahigh flexibility.More importantly,the newly prepared hydrogel retained the photochromic properties of the cesium tungstate nanosheets.The color transitions could be readily controlled by UV laser irradiation and were completely reversible via laser exposure or dark treatment.The nanocomposite hydrogel with its excellent photochromic properties and ultrahigh flexibility will have great applications in flexible photochromic devices.The synthetic procedure is simple and has promises to be extended to developing other hydrogels with various new functionalities.