| Hydrogels is a kind of three-dimensional(3D)cross-linked porous polymer material with network structure and composed of natural or synthetic materials.Hydrogels have excellent water absorption,good transparency,high hydrophilicity,unique mechanical properties,biocompatibility and similarity to human tissues due to their large number of hydrophilic groups and special network structures.These characteristics make hydrogels show various potential applications in different fields,such as the preparation of wearable devices,bionic robots,electronic skin and biomedical applications.However,the traditional single function hydrogel can’t meet the needs of practical applications.A lot of effort was made to improve the performances of hydrogels materials and the applications as electronic skin and strain sensors to detect human health.Based on a brief review of multifunctional hydrogels,the following work has been completed in this paper:1.A multifunctional adhesive hydrogel with high toughness and conductivity was designed by introducing chitosan and iron ions into the acrylated-adenine polyacrylamide chain.The prepared hydrogel material can adhere to the surface of various solid matrices and show good mechanical properties.Its maximum adhesion strength to wood is 11.17 KPa,fracture stress is 0.11 MPa,and toughness is 0.84 MJ/m~3.The hydrogel can be stretched to more than 1400%of its original length without breaking.In addition,the hydrogel also has good repeated adhesion and fatigue resistance.Due to the presence of Fe(Ⅲ)and Cl~-,the hydrogel also has certain conductivity,which can be used for human motion detection.2.By introducing tannic acid coated graphitized carbon nanotubes into the network structure composed of polyacrylic acid and carboxymethyl cellulose,the basic framework of the hydrogel network was constructed,and a multi-functional hydrogel with high tensile properties,self-adhesion,strain sensitivity and conductivity were prepared.The chemical cross-linking constructed the framework for the network of the hydrogel.The dynamic physical cross-linking of the multiple hydrogen bonding among TA,CMC,and PAA together with theπ-πstacking between CNTs could dissipate energy effectively.The hybrid of chemical cross-linking and physical crosslinking endowed the hydrogel excellent toughness,high stretch-ability,and self-adhesion.The strain of the hydrogel can reach 1385%,and the self-adhesion force on the wood surface can reach 16.65 KPa;With the increase of the content of CNTs,the conductivity of the hydrogel gradually increases to 5.13 S/m.Because of its adhesion and conductivity,it is used as a strain sensor to detect different motion modes of the human body.3.A multifunctional transparent hydrogel with high tensile strength,toughness,adhesion and conductivity was prepared by a two-step method using sodium alginate,tannic acid,polyacrylic acid,carboxymethyl cellulose and aluminum trichloride.The hydrogel can be attached to various organic and inorganic materials.The highest adhesion strength of the hydrogel to the iron sheet is 22.33 KPa,the fracture stress is0.16 MPa,and the toughness is 1.01 MJ/m~3.In addition,hydrogels exhibit repeatable and persistent adhesion to human skin,and can be completely peeled off without any residue,irritation or allergic reaction.In addition,hydrogels have good strain sensitivity.The research shows that both large-scale and small-scale movements of the human body can be monitored by self-adhesion directly attached to various parts of the human body.This work provides a new prospect for the design of biocompatible hydrogels with transparent,stretchable,self-adhesive and strain sensitive properties. |
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