Polymer hydrogel is a soft material with a three-dimensional network structure that can absorb and retain a large amount of water. Polymer hydrogels have good biocompatibility, mechanical properties and important application value in biomedical and bioengineering fields. Self-healing hydrogels are smart hydrogels that respond to external stimuli and repair their own damage. Compared with the traditional hydrogel, the self-healing hydrogel has the property of repairing damage, and received extensive attention in the scientific field in recent years. Dynamic chemistry-based self-healing hydrogels are novel self-healing hydrogels that can reshape three-dimensional network structures by dynamic covalent or non-covalent bonding to repair damage. The new self-healing hydrogel can quickly repair its own damage and has good environmental adaptability, laying the foundation for the development of self-healing hydrogels as multifunctional new materials. The research progress of recent self-healing hydrogels based on dynamic chemistry was reviewed in this paper, especially focusing on the updated development on self-healing hydrogels based on hydrogen bonds, metal coordination interactions, host-guest interactions, ionic bonds, hydrophobic interactions, imine bonds/acylhydrazone bonds, borate bonds and disulphide bonds, and meanwhile, the problem of self-healing hydrogels was put forward, and the future direction of development was finally predicted.

Silk fibroin is a natural polymer with biocompatibility, biodegradability and other excellent properties, which is a promising material in the fields of medicine, food and cosmetics, etc. In this work, the preparation techniques, material structure, properties and development trend for silk fibroin and its composites with natural biological protein, inorganic material, synthetic polymer, carbon nanotube and graphene oxide were introduced, respectively. The preparation principles of materials were explained, with an emphasis on the relationship between preparation methods and properties. The interaction mechanism between individual composites was analyzed, and the application on tissue engineering, drug application, anticoagulant materials and other aspects were also summarized. According to the key factors which restrict the research and development of silk fibroin and its composites, the promising future development ways were proposed, for example, realizing the scale production, developing the intelligent materials and restructuring modification of silk fibroin from the gene aspect.

The stimulus-response composite is a kind of intelligent material, which usually possesses the characteristics of self-perception, autonomous response, shape memory, adaptive and self-healing. The stimulus-response materials used in 4D printing were reviewed in this paper, and the application research progress of 4D printed shape memory composite hydrogels and shape memory polymers (SMPs) and their composites was focused. Finally, the application status of 4D printing in the biomedical and aerospace fields was summarized, and the development trend and application prospect of 4D printing were prospected. 4D printing is an emerging manufacturing technology. Although various printing methods, printable smart materials and driving methods have been developed, 4D printing still faces many challenges in practical engineering applications. Novel printing technologies, smart materials, structural design and modeling software need to be developed to facilitate the practical application of 4D printing in the fields of soft robotics, biomedicine, aerospace and intelligent electronic equipment.

Hemicellulose-based hydrogels are three-dimensional networks formed by crosslinking hydrophilic polymers with tunable swelling behavior, acceptable biocompatibility and mechanical properties, and have received much attention in the field of soft materials especially in hemicellulose-based materials.Herein, recent advances and developments in hemicellulose-based hydrogels were reviewed.The preparation methods, mechanism of their gelation process, and the performance of the hemicellulose-based hydrogels were presented from both chemical and physical cross-linking approaches, while the differences in various initiation systems such as light, enzyme, microwave irradiation and glow discharge electrolysis plasma in chemical cross-linking were compared.The latest applications of hemicellulose-based hydrogels in drug-controlled release, wound dressing, water purification, 3D printing dispersions, etc, were introduced, respectively.Finally, the challenges in the development of hemicellulose-based hydrogels were summarized briefly and future prospect was also given, which provides a reference for the synthesis of new hemicellulose-based hydrogels.

Chitosan-based ternary intelligent hydrogels of pH/temperature-sensibility were prepared on the basis of chitosan/polyvinylpyrrolidone(CS/PVP)hydrogels with polyvinyl alcohol(PVA)introducing,using glutaraldehyde as crosslinking agent and ammonium ceric nitrate as initiator. The results indicated that the introduction of PVA increased the concentration of CS in the hydrogels significantly and made the temperature-sensitive grade increase. Especially, the hydrogels indicated obvious temperature-sensitivity at 35℃. Under the optimal conditions, that is, 6.25%PVA(mass fraction, compared to PVP), 5.1% initiator, 0.4% cross-linking agent, 80℃ and 6h, the maximum swelling ratio of hydrogels was about 1500%. Thermo-sensitive and pH-sensitive experiments showed that the hydrogels were of excellent thermo-sensibility and pH-sensibility. The chitosan-based ternary hydrogels were of four grades temperature-sensitivity and good pH-sensitivity with the abrupt change point at 2.0.

Photonic crystal is a kind of ordered material which consists of two or more periodic arranged refractive index materials, and the propagation of light can be controlled by changing its average refractive index or lattice spacing. The molecularly imprinted photonic crystal chemical sensors based on the combination of responsive photonic crystal structure and molecular imprinting technique have attracted research interests due to their strong specificity, high sensitivity and self-expression ability, which also provide a novel strategy for the trace detection. In this review, the two- and three-dimensional photonic crystal sensor materials were introduced, and the preparation, properties and applications of molecular imprinted photonic crystal(MIPC) were reviewed. The future research focus such as the improvement of resolution and repeatability of MIPC visual detection materials was analyzed and prospected at last.

Poloxamer is a thermo-sensitive polymer that can form gel at a concentration of 15.0%(mass fraction, the same as below)-30.0%.In order to decrease the gelatinization concentration and improve drug release properties of poloxamer at body temperature, thermo-sensitive N-acetyl glycol chitosan/poloxamer composite hydrogel was prepared by complexing N-acetyl glycol chitosan with poloxamer 407 (GC/P₄₀₇).The structure, thermo-sensitivity, mechanical properties, morphology and in vitro drug release properties of GC/P₄₀₇ were characterized by FT-IR, tube inverting method, rheometer, SEM and UV-vis spectroscopy. The GC/P₄₀₇ solution shows reversible thermo-sensitive sol-gel transition behavior, and the sol-gel transition temperature is well controlled in the range of 25-37℃ by regulating the ratio of GC/P₄₀₇, which shortens the gelation time and the gelatinization concentration(6%) of poloxamer 407 at body temperature. GC/P₄₀₇ composite hydrogel, which has a highly porous three-dimensional structure with pore size of 10-60 μm as demonstrated by SEM, exhibits high mechanical properties. In addition, the GC/P₄₀₇ composite hydrogel shows sustained release behavior of the anticancer drug gemcitabine, and the release time of the drug-loaded gel can reach 72 h. GC/P₄₀₇ composite hydrogel shows the potential for biomedical application as injectable drug delivery carrier.

Cellulose nanocrystal (CNC) plays a more and more important role in the process of designing and assembly of functional materials, due to its high strength and modulus, controllable structure, feasible modification, biocompatibility and biodegradability. As a kind of macromolecule system with "intelligent" behavior, the stimuli-responsively functional materials make a sensitive response when stimulated by the external environment, and show the corresponding function. With the addition of CNCs, not only the mechanical properties of CNC-based functional materials are greatly improved, but also the hydroxyl and carboxyl groups on the surface of CNCs provide a convenient way to enrich the stimulus response source of these functional materials. Herein, combining with the chemical structure of CNC, the synthesis of CNC-based stimuli-responsive functional materials was comprehensively summarized. Meanwhile, the recent developments of single or multiple stimuli-responsive functional materials based on CNCs, such as water-, thermal-, pH-, light-responsive functional materials were summarized, with the stimulate switch taken as the main line. Finally, it was pointed out that future research would focus on improving the surface-modification efficiency of CNC, and broadening multi-stimulus responsiveness of CNC-based functional materials. The preparation of CNC-based functional materials with high performances will be significant in the future research as well.

Poloxamer is a thermo-sensitive synthetic polymer that can achieve sol-gel transition with temperature change, but its relative molecular mass is low, and the hydrogel structure is difficult to maintain for a long time. The thermo-sensitive sodium alginate/poloxamer composite hydrogel (SA/P₄₀₇) was synthesized by mixing poloxamer with sodium alginate. The chemical structures, temperature sensitivity, microscopic morphology, dynamic viscoelasticity and in vitro drug release behaviors of sodium alginate/poloxamer composite hydrogels were investigated by FT-IR, test tube inversion, SEM, rheometer and UV-Vis spectroscopy. In addition, the swelling properties of sodium alginate/poloxamer composite hydrogels were also studied. These results show that the sodium alginate/poloxamer composite hydrogel is thermo-sensitive, and the gelation concentration (mass fraction is 6%) of poloxamer at body temperature can be reduced by adding sodium alginate. By controlling the mass ratio of sodium alginate and poloxamer, the sol-gel transition temperature can be kept between room temperature and body temperature (25-37 ℃), and the gelation time can be shortened to 84 s. The sodium alginate/poloxamer composite hydrogel has a structural feature of high porosity and interconnected pores, and its pore size ranges from 20 μm to 80 μm. With the increase of sodium alginate, the swelling rate of the sodium alginate/poloxamer composite hydrogel is gradually decreased. The sodium alginate/poloxamer composite hydrogel shows sustained release of the anticancer drug gemcitabine, and the drug release time can reach 72 hours. Sodium alginate/poloxamer composite hydrogel has an important application prospect in the field of injectable carriers for sustained drug release.

The four types of hydrogels using acrylamide(AM) and isopropylacrylamide(NIPAM) as monomer, methylenebisacrylamide (MBA) and inorganic nanoclay lithium magnesium silicate hydrate (LMSH) as chemical and physical crosslinker, respectively, were prepared by freeradical polymerization in aqueous solution. The results show that, comparing with hydrogels crosslinked by MBA, the polyAM and polyNIPAM hydrogels using LMSH as physical crosslinking agent presents higher swelling ratios and lots of pore. The adsorption amount of crystal violet (CV) on polyAM and polyNIPAM hydrogels increases 58 times. In terms of adsorption and using effect, polyNIPAM hydrogel crosslinked by LMSH is the best choice for removing CV dye.

Carboxymethyl chitosan is an important chitosan derivative with good biocompatibility and degradability, and has a wide range of biomedical applications. In this study, water-soluble carboxymethyl chitosan derivative that can be photo-crosslinked by UV irradiation was synthesized. Methacrylated carboxymethyl chitosan (M-CMCS) was synthesized by N-methacrylation of carboxymethyl chitosan (CMCS). The chemical structures of M-CMCS were characterized by ¹H NMR and FT-IR. The M-CMCS hydrogels with different degrees of crosslinking was prepared by UV-triggered photo-crosslinking. The microscopic morphology, mechanical properties, swelling properties, enzymatic degradation properties and in vitro drug release behaviors of M-CMCS hydrogels were investigated by SEM, rheometer, and UV-Vis spectroscopy, respectively. The results show that the degree of methacrylation is gradually increased as the molar ratio of glycidyl methacrylate to carboxymethyl chitosan increases. M-CMCS hydrogels have the structure of high porosity and interconnected pores with the pore size of 1-20 μm. The swelling ratio of M-CMCS hydrogels is decreased as the degree of crosslinking increases. M-CMCS hydrogel can be slowly degraded by lysozyme, and the degradation rate is decreased by increasing the degree of crosslinking. M-CMCS hydrogels show sustained release behavior for anticancer drug gemcitabine, and the drug release can be extended to 4 days. Photo-crosslinked M-CMCS hydrogels show great promise for drug release and tissue engineering.

Self-healing polymer materials are able to self-repair damage and recover themselves after cracks generating to maintain their structural and functional integrity. According to whether additional repair agent is added, self-healing polymers are mainly divided into two categories, namely extrinsic- and intrinsic-based polymers.The key materials of electrochemical energy storage devices will experience irreversible mechanical damage in extreme condition applications, for example, the energy storage device more prone to physical damage inwearable devices during the multiple bending and deformation processes. These problems severely reduce the stability of energy storage and delivery, and shorten the life of the devices. Therefore, the application of self-healing polymers in electrochemical energy storage devices to improve the stability and life of devices has become one of the research hotspots in recent years. Herein, this article summarizes the repair mechanism of self-healing polymer materials (capsule-based, vascular-based, and intrinsic polymers), with main focus on intrinsic self-healing polymer and its research progress in the field of electrochemical energy storage, which based on molecular interactions to achieve multi-time reversible healing without any additional repair agent.The self-healing electrode and electrolyte system were reviewed respectively, and then the self-healing mechanism and its influence on the electrochemical performance of energy storage devices were described. The research progress of self-healing functional polymer as high specific energy electrode binder, interface modification layer and self-healing electrolyte were summarized in detail. Finally, the future perspectives regarding the future development of self-healing polymer materials were also discussed.

Montmorillonite(MMT) was utilized to absorb three types of cationic photosensitizers, namely, meso-tetra(4-N-methylpyridyl)porphyrine tetratosylate (TMPyP), Zn(Ⅱ) meso-tetra (N-methyl-4-pyridyl) porphine tetrachloride (Zn-TMPyP) and methylene blue (MB), the as-obtained mixtures were then evenly dispersed in aqueous polyvinyl alcohol-styrylpyridine salt condensate (PVA-SbQ) solution, corresponding photoactive MMT/PS hydrogels were prepared by the assay of UV cross-linking eventually. Transmission electron microscopy (TEM) was employed to analyse morphology of MMT and one as-prepared MMT/PS hydrogel. Scanning electron microscopy (SEM) and thermogravimetric analysis (TGA) were applied to analyse the internal morphology and thermal properties of the as-prepared hydrogels. Finally, swelling properties and antibacterial effect against staphylococcus aureus (S. aureus) were investigated. The results show that three photoactive MMT/PS hydrogels are successfully prepared with good swelling properties. The as-prepared hydrogels exhibit inactivation against S. aureus to some extent, furthermore, the hydrogel which immobilizes Zn-TMPyP reveals best inactivation efficacy, with a sterilization rate of 98.49%.

According to the material research that human articular cartilage is expected to be repaired after injury, a new artificial cartilage-like material was prepared by thermal polymerization in this experiment. Under water bath insulation and initiator conditions, hydroxyethyl methacrylate(CH₂＝CCH₃COOCH₂CH₂OH, HEMA) and medical glycerol(C₃H₈O₃) were polymerized into a new gel. And the surface morphology was compared with that of porcine cartilage, and the mechanical properties such as compressive strength and elasticity were tested. By analyzing and characterizing with FTIR spectra, the host of gel is still PHEMA, and glycerol exists in gel phase. The hardness of gel decreases with the increase of glycerol ratio, while the surface roughness of gel increases. When the mass ratio of HEMA to glycerol is 1:1-1:3, the hardness of the gel is close to that of pig cartilage, and the surface is smooth under the conditions of 1:1 and 1:2. Gels of four mass ratios have good compressive strength and elasticity. When the mass ratio is 1:1, the compressive properties and comprehensive properties are the best. The experimental results indicate that PHEMA and glycerol gel polymers have good mechanical properties as artificial cartilage materials, they may provide further investigation for clinical trials.

3D printing as an important, fast-growing manufacturing technology is triggering major innovations in many fields, such as medicine, aerospace, automobile and food. The main advantages of 3D printing include design freedom, mass customization, waste minimization, and rapid prototyping, etc. The personalized features enable 3D printing to prepare products based on the patient's condition to help the patient recover. With the increasing demand for precision and personalized medicine, 3D printing is gradually being applied to implant manufacturing, diagnostic platforms and drug delivery systems. Therefore, this article outlines the development of 3D printing technology, which introduces medical materials that can be used for 3D printing, and the application of 3D printing technology in the medical field. Finally, the challenges and development prospects of 3D printing technology in the medical field are summarized and discussed.

Functional polymer material is a type of polymer materials with special functions such as catalysis, conductivity, photosensitivity, and biological activity. They have the function of transmitting, converting, or storing substances, energy, and information. Functional polymer materials have the characteristics of light weight, numerous varieties and strong specialty, which make them widely used in machinery, information technology, biomedicine and other fields. The development of functional polymer materials is very rapid. In order to meet the needs of new technologies in various fields, functional polymer materials are gradually developing towards multi-function such as electromagnetic materials and photothermal materials. With the emergence of smart polymers, functional polymer materials are gradually being developed towards intelligence, such as self-healing functional polymer materials and shape memory materials. The research progress of functional polymer materials in recent years was summarized in this article and their applications were briefly described, with emphasis on reactive functional polymer materials, optical functional polymer materials, electrical functional polymer materials, biomedical functional polymer materials, environmentally degradable polymer materials, shape memory polymer materials and smart polymer hydrogel. At present, most functional polymer materials only have traditional functions such as photoelectricity or special functions such as shape memory. It is believed that functional polymer materials with both traditional and special functions will be the development direction of future materials.

Additive manufacturing technology as revolutionary manufacturing technology has attracted much attention.This technology transformed traditional processing design and manufacturing concepts and promoted the development of intelligent manufacturing. Intelligent material is a kind of material that has the ability of self-perception, autonomous response, self-healing and adaptation. The combination of intelligent materials and additive manufacturing technology can realize the integrated manufacturing of three-dimensional smart devices with the ability to sense external stimuli or environmental activation. This technology has been widely used in fields such as biomedical devices, flexible electronics, soft robotics, and other fields.Additive manufactured intelligent materials, and the advantages and problems of additive manufactured intelligent materials of metals, polymers, and ceramics were reviewed.As a technical means to realize the organic integration of design, material and structure, additive manufacturing technology will become the key to promote the development of intelligent materials.

The hemicellulose-based magnetic hydrogel was prepared by free radical polymerization and in situ co-precipitation from corn cob. The properties of the magnetic hydrogel were characterized by means of ICS, scanning electron microscopy(SEM) and universal tensile testing machine. Moreover the adsorption properties on methylene blue were studied. The results show that the hemicellulose-based magnetic hydrogel has super-paramagnetism, with a maximum saturation magnetization intensity of 21.83 A·m²/kg and a maximum compression strength of 0.119 MPa. The adsorption properties on methylene blue are good as well and the removal rate reaches 97%. The prepared hemicellulose-based magnetic hydrogel has good swelling properties, super-paramagnetism and removal efficiency of methylene blue. Furthermore it has better application prospects.

The biological scaffolds of tissue engineering are required to have good biocompatibility, matched mechanical properties, as well as morphology and microstructure for cell growth and reproduction. Although a large number of biomaterials have been developed to prepare tissue-engineering scaffolds, the forming problems and poor mechanical properties of the scaffolds still seriously limit the development of tissue engineering. The sodium alginate was used as raw material, and its mechanical properties were enhanced by agarose. The structure and morphology of sodium alginate/agarose composite hydrogels with different ratios were studied, the mechanical properties were tested. In addition, the composite hydrogel scaffold was formed by direct ink writing, and the size of the microscopic pores in composite hydrogels were designed and observed. The results show that the composite hydrogels with different ratios have little difference in water content, all around 90%. Apart from the pure agarose gel and the composite gel with a volume ratio of 1:2, the surface and cross section of the composite gel in other ratios are relatively rough. Agarose can enhance the composite gel to a certain extent, and the composite gel with the volume ratio of sodium alginate to agarose of 2:1 has the highest compression modulus, which can reach 0.353 MPa. The decomposition of calcium carbonate created submicron pores in the composite hydrogel, therefore the prepared composite hydrogel has rough surface and micro-pores, which is conducive for cell growth and reproduction.

Most common chemiresistive gas sensors, based on metal oxide semiconductors, have high energy consumption and poor gas response, which are not suitable for gas detection in factory. With the development of the research on 3D graphene, 3D graphene and its composites become a hotspot of gas sensor researches, because of its large specific surface area and high electrical conductivity. In this paper, the fabrication, performance and application of gas sensors based on 3D graphene and its composites were summarized.At the same time, in view of the slow response recovery speed and small production scale of the current 3D graphene-based gas sensor, solutions such as miniaturization and intelligent production of the sensor chip were proposed, so that it can become the front end of the industrial Internet of Things in the future.

Degradable hydrogels are widely used in the repair and regeneration of articular cartilage because of their good biocompatibility and biodegradability. Three application strategies of degradable hydrogels in cartilage tissue engineering were focused in this review. Firstly, the proteoglycan materials and nanocomposite materials for in-situ formed injectable hydrogels were reviewed. Secondly, the advantages and disadvantages of traditional technology for tissue engineering scaffolds and the preparation methods of combination of various technologies were systematically summarized. Importantly, the research progress of 3D printed tissue engineering scaffolds from pure cartilage to bone/cartilage integration, from single layer to multi-layer in recent years were summarized. Finally, the limitations of degradable hydrogel as articular cartilage scaffold material in micro-directional structure and bioactivity functionalization were discussed.It was prospected that developing highly biomimetic gradient scaffolds with multi-material, multi-scale and multi-inducement will be an important research direction of articular cartilage tissue engineering in the future.

Microneedles (MN) as a minimally invasive device consisting of a micro-raised array, can penetrate the cuticle to the epidermis and dermis, and which has the advantages of safety, painless, minimally invasive, self-administration and convenience. As a new kind of microneedles, hydrogel microneedles have attracted more attentions in the medical field due to its excellent performance. Hydrogel microneedles have good biocompatibility and mechanical properties, and can be completely removed after skin action without residual polymer in the body. Its unique swelling property can realize minimally invasive extraction of human detection substance and slow release of drugs, which can play a huge role in the field of personal health monitoring and drug controlled release in the future. The mechanism of action, design, preparation and application of hydrogel microneedles were reviewed in this paper, focusing on the current design parameters of hydrogel microneedles and their applications in drug delivery, extraction monitoring and wound healing, and the problems of hydrogel microneedles in skin infection risk, pharmacokinetics and wearing comfort were pointed out. In the future, the key research direction is to combine with intelligent devices to realize both human body monitoring and intelligent drug controlled release on the microneedle patch.

Human skin can sense the information from the environment and play a significant role in the contact with the outside world. Electronic skins, which mimic the characteristics of human skin and the ability to perceive the environment have a wide range of applications in the fields of medical monitoring, bionic prostheses and robotic tactile perception. Compared with traditional wearable sensors, electronic skin is lighter, more flexible, more malleable, and has the characteristics of wireless, transparent, and compatibility with human skin, therefore, has become one of the emerging research fields. The electronic skin can continuously sense large number of physical and biochemical parameters of the human body, human motion and gas to monitor human health, sports condition and surrounding gases in various environments in real-time. In this review, the state-of-the-art of the materials used to making electronic skins, including zero-dimensional (0D), one-dimensional (1D), two-dimensional (2D) and three-dimensional (3D) micro/nano-materials, polymeric materials, hydrogel materials and their composites, were discussed, and the practical applications of the electronic skin constructed based on these core materials were concluded in terms of health monitoring, motion monitoring as well as gas monitoring. It was pointed out that there are still some remaining technical problems in the research process of electronic skin such as high cost and complex process.The development trend of electrode skin was towards multi-function and simultaneous detection of multiple external stimuli, and it had broad application prospects in the fields of medical equipment robbotics and future manufacturing.

Collagen, sodium alginate and hyaluronic acid are natural-derived polymer materials with good cell compatibility and bio-safety, which are widely used in cell culture, tissue engineering and drug delivery, and so on. Pure collagen has poor mechanical properties. When preparing collagen and sodium alginate to form a composite hydrogel material, the mechanical properties and porosity of the hydrogel scaffold can be improved by adjusting the degree of cross-linking of sodium alginate and Ca²⁺ mimicking extracellular matrix. The Young's modulus and the sol-gel transition temperature of the hydrogel were characterized by PIUMA nanoindenter and DHR rheometer in this study. Microscopic images of endothelial cells expressing red fluorescent proteins and mesenchymal stem cell expressing green fluorescent proteins were captured with Olympus fluorescence microscope after cell cultured for 0 day, 3 days, 5 days and 7 days in hybrid hydrogel microenvironment, and the images of endothelial cell spheroid growth diffusion after cell cultured for 1 day, 6 days and 9 days. The results show that the hybrid hydrogel is cytocompatible. The Young's modulus of the hydrogel is (600±81) Pa and its sol-gel transition temperature is 23.2℃. In conclusion, type Ⅰ collagen/sodium alginate/hyaluronic acid hydrogel has good cytocompatibility for endothelial cells and mesenchymal stem cells, and can be used as an ideal scaffold material for cell 3D culture. The Young's modulus and sol-gel transition temperature of the hydrogel have no damage to cell viability, which can be used as an in vitro model for studying angiogenesis and has important application prospects in vascular tissue engin-eering.

Hydrogel is a cross-linked three-dimensional network hydrophilic polymer material, which can absorb and retain a large amount of water and maintain a certain shape. In recent years, with the depletion of petroleum resources and the increasing attention of human beings to environmental issues, natural or modified polymer synthetic polymer hydrogels have become a research hotspot. Cellulose and its derivatives are a large class of renewable natural polymer materials, which have the characteristics of rich resources, wide variety, non-toxic and renewable, etc. The synthesized cellulose-based hydrogel has good water absorption, water retention, biocompatibility and biodegradability, etc., which can be used in medical, environment, agriculture and other fields. The research progress of the construction and application of cellulose-based hydrogels in recent years was reviewed in this paper. The microscopic network structure is combined with the macroscopic properties of the hydrogel. The mechanical properties, swelling properties and adsorption properties of the single network, interpenetrating network and semi-interpenetrating network cellulose-based hydrogels were summarized, and their applications in medical, environmental, agricultural and electronic fields were introduced. The development of cellulose-based hydrogels with both mechanical properties and biocompatibility, and the development of more green economic methods for the synthesis of cellulose-based hydrogels for industrial applications were proposed.

Because of its light weight, flexibility, and good contact with electrode, solid polymer electrolyte (SPE) has become a potential material for the development of electrochemical devices with high energy density, high safety and high flexibility, and has been paid extensive attention in recent years. However, defects such as low ionic conductivity and poor mechanical properties have also become the problems that limit its further commercialization. It is possible to solve these problems by forming a composite system of polymers by means of crosslinking, blending, copolymerization, etc. Therefore, in this paper, the mechanism of ionic conductivity in polymers was briefly introduced in order to explain the strategies to solve the above problems from the point of principle. Then, the applications and modification strategies of a variety of polymer-based composite electrolytes in electrochemical devices in recent years were reviewed. Finally, the problems of basic research and practical application faced currently by the composite SPEs were discussed and the solutions to these problems were given. It is hoped that this review can provide ideas for the design and preparation of future composite SPEs.

Industrial wastewater has brought huge disasters to water bodies and soil, and seriously affected the growth of crops. In order to obtain clean water, a stable, effective and sustainable treatment agent must be prepared to control water pollution. The lignin-based hydrogel adsorbent was prepared on polyacrylic acid by free radical polymerization of sodium lignosulfonate and chitosan, which was applied to remove Pd²⁺ and Cd²⁺. The orthogonal method was used to optimize the content of sodium lignosulfonate, chitosan, cross-linking agent and initiator. Fourier infrared spectrometer, scanning electron micrograph, thermal analyzer and Zeta potentiometer were used to characterize the adsorbent. The effects of different conditions on the adsorption of Pb²⁺ and Cd²⁺ by lignin-based hydrogels were discussed, and the kinetics and isotherm models on the basis were established. The results show that when the adsorbent is 0.015 g, the concentration of heavy metal ions is 100 mg·L^-1, and the pH value is 7, the adsorption capacity for Pd²⁺ is 367 mg·g^-1 and the adsorption capacity for Cd²⁺ is 296 mg·g^-1. Simultaneously, it is revealed that the adsorption process of lignin-based hydrogels is an adsorption mode in which electrostatic adsorption is supplemented by chemical adsorption.

Potassium diformate (KDF) is a novel substitute for antibiotics, which is not widely used in livestock production. The P-type molecular sieve (Zeolite P) was prepared by hydrothermal method with loading KDF and dispersed in the carboxymethyl cellulose (CMC) solution. The dispersed CMC mixed solution was added dropwise to the FeCl₃ solution for cross-linking. Chitosan-carboxymethyl cellulose-Zeolite P-potassium diformate pH-sensitive hydrogel antibacterial microspheres were prepared by coacervation method. FT-IR, TGA and SEM results show that CS and CMC form the structurally stable polyelectrolyte complex through ionic bonds, and Zeolite P is included in the CMC matrix. The difference in swelling study indicates that the hydrogel microspheres have high pH-sensitivity and can be applied for sustained-release under different pH value. The slow-release kinetics study shows that antimicrobial microspheres have a certain sustained-release effect on KDF. The first-order kinetic model and the Higuchi model fits well with release data. In vitro antibacterial experiments, the antibacterial microspheres display significant antibacterial property against Escherichia coli and Staphylococcus aureus in the concentration of the antibacterial solution at 24 mg/mL and 48 mg/mL. Antibacterial microspheres can effectively inhibit the growth of bacteria, and the antimicrobial microsphere model provides a theoretical basis for the use of KDF.

Nano-hydroxyaptite/polyvinyl alcohol (n-HA/PVA)composite hydrogels were prepared and the swelling properties of n-HA/PVA were studied. The result showed that the water content, swelling ratio and dissolution ratio of the composite hydrogels were affected by content of n-HA in the hydrogel and freezing-thawing cycles’ time. The water content, swelling ratio and dissolution ratio were inversely proportional to the content of n-HA in the hydrogels, and the water content and dissolution ratio were also inversely proportional to the freezing-thawing cycles’ time, while the swelling ratio increased with the freezing-thawing cycles’time.

Flexible energy storage devices are at the forefront of next-generation power supplies, one of the most important components of which is the gel electrolyte. The dual network gel electrolyte for PAM/P123 zinc ion batteries was prepared by free radical polymerization. It was found that the addition of a small amount of triblock copolymer P123 can macroscopically improve the tensile strength, toughness and compressive strength of the gel electrolyte. Microscopically, the gel skeleton forms 0.6 μm mesopores and increases the surface pore distribution density, thereby improving the wettability of the electrolyte. The PAM/P123 series electrolytes not only have a high average swelling rate, but also have a higher conductivity than pure PAM electrolyte in the range of -30℃ to 65℃. Among which, PAM/P123-2 is a series of electrolytes with the best performance, with an average swelling rate of 1920.79%, and the conductivity at 0℃ is 36.2 mS·cm^-1.The Zn/MnO₂ battery prepared by using PAM/P123-2 gel electrolyte is stable during cycling at 0℃, with the capacity retention rate reaching 82.39% after 1000 cycles.

The development of energy storage devices that can withstand large and complex deformation is crucial for emerging wearable electronic devices. At present, hydrogels made of conductive polymers have achieved the fusion of high conductivity and versatility during processing. A simple two-step copolymerization method was used to successfully construct a hydrogel supercapacitor with a rich microporous structure: polyvinyl alcohol(PVA) and polyacrylamide(PAM) form a double cross-linked network hydrogel, which endows rigid polymer aniline with flexibility. In addition, polyacrylamide improves the mechanical strength of polyaniline-based hydrogels, making polyaniline-based(NPP)hydrogels have good mechanical and electrochemical properties, and the tensile strength and specific capacitance are 0.3 MPa and 269.12 F·g^-1 under 1 A·g^-1, respectively. The addition of polyaniline(PANI) reduces the internal resistance of polyvinyl alcohol and polyacrylamide double cross-linked network hydrogel(PP) electrode, and its modified resistance value is 39.184 Ω, which makes the NPP hydrogel realize higher electron transmission capacity. The flexible development and integration of such hydrogels provide an alternative strategy of energy systems for diverse applications such as supercapacitors.