Design And Application Of High-Performance Flexible Electronic Skin Based On MXene

Flexible electronic skin inspired by skin functions can perceive external changes(temperature,humidity,pressure)and timely feedback,which is widely used in health monitoring and diagnosis,motion tracking,intelligent prosthesis,soft robots.However,the elastic modulus of the traditional flexible substrate(silicone rubber or polyurethane)used for electronic skin is much higher than that of human tissue,which makes it unable to fit perfectly with the skin interface and may cause tissue damage and other problems.Hydrogels with good flexibility and organizational similarity become the ideal candidate material to replace traditional flexible substrate,but only covalent or supramolecular hydrogel often can not have excellent mechanical strength and stretchability at the same time.Therefore,to solve above problems,high performance sensors were prepared by reasonable designing hydrogel composition and network structure or using natural silk fibroin(SF)with high mechanical properties,with complexing appropriate proportion of conductive Ti₃C₂ MXene.The adhesion,self-healing and electrical properties of high-performance sensors were explored,and showed potential application as electronic skin.The main research contents are as follows:(1)Based on the high conductivity and good hydrophilicity of Ti₃C₂ MXene,a covalent crosslinking network structure composed of PEG(DEGMA,OEGMA)monomers and MA-GFF?FF polypeptide nanofibers was constructed by the oxidative crosslinking reaction between MA-DOPA molecules.The?-folded structure formed by non-covalent bond forces in MA-GFF?FF fibers formed a supramolecular crosslinking network.Thus a covalent-supramolecular hybrid hydrogel sensor based on MXene was prepared.Among them,the supramolecular network formed by MA-GFF?FF fibers can balance the energy dissipation as a reversible dynamic network so that the hydrogel sensor has good mechanical strength and tensile property(tensile strain 700%;elastic modulus 94.21 k Pa).When the hydrogel sensor is stimulated by stress or strain,it showed rapid and efficient self-healing(self-healing time 0.2 s,self-healing efficiency 98%).Inspired by the adhesion mechanism of mussel,MA-DOPA made the hydrogel good adhesion on porcine skin,tissue,glass,steel,rubber,polytetrafluoroethylene.And the hydrogen bonding force between MA-DOPA and surface functional groups of MXene can effectively promote the synergic movement of MXene and hydrogel matrix,ensuring the stability and linear correlation of electrical signals in the application process.In addition,due to the strong hydrogen bonding force between DEGMA/OEGMA monomers and water molecules,hydrogels are still flexible and exhibit good frost resistance after being stored at-20 o C for 24 h.Hydrogel sensors can be used as electronic skin for motion monitoring and speech recognition at low and normal temperatures.(2)Based on the excellent mechanical properties of SF,Ti₃C₂ MXene composite silk fibroin-based flexible sensor was prepared by taking advantage of the strong interaction between natural plant polyphenol TA with SF and the water absorption and retention ability and further promoted the formation of?-folding of Ca²⁺.The mechanical properties of the silk fibroin-based sensor(171.3 k Pa;1048.7%)were further enhanced through the SF naturally existing crystalline and amorphous regions,the introduction of Ca²⁺and the appropriate addition of Ti₃C₂ nanosheets with nano-strengthening mechanism.At the same time,TA also made it have good(underwater)adhesion,self-healing,antibacterial property,which provided safe and powerful guarantee for long-term and underwater application.In addition,as a wearable electronic skin,the sensor can be woven into a smart fabric using a wet spinning process.Silk fibroin-based electronic skin can accurately monitor the changes of human joint movement,micro-expression and micro-movement in real time.