Construction Of Mussel Inspired Adhesive Hydrogels And Flexible Sensors

Flexible sensor is a kind of device with high flexibility and toughness,which can transform external stimuli such as strain,stress,chemical substances into detectable signals(such as resistance,color,voltage,capacitance,etc.)Due to its unique flexibility,flexible sensors have potential applications in wearable devices,health monitoring,human-computer interface,soft robots and other fields.At present,the widely studied flexible sensor is based on the change of resistance or capacitance caused by mechanical deformation.In order to obtain high performance strain sensors,it is necessary to develop strain sensitive deformable materials.As a new soft material,conductive hydrogel has been widely used in flexible sensors because of its biocompatibility,flexibility and electrical conductivity.However,most of the sensors constructed by conducting hydrogels lack adhesiveness and may cause slippage in testing,which will affect the accuracy and convenience of sensing.Inspired by the adverse adhesion characteristics of mussel,polydopamine(PDA)is introduced into hydrogels to prepare adhesive hydrogel and to build sensors as a simple and universal method.The reversible interaction between catechol rich in PDA and polar groups such as amino,carboxyl and hydroxyl groups on the substrate can make the sensor adhere to different material surfaces.However,at present,the adhesive hydrogels based on PDA have poor mechanical properties,single function,short service life,uncontrollable adhesion,and unable to meet the requirements of adhesion under low temperature environment,which limits their practical use in sensor monitoring.Therefore,building an adhesive hydrogel sensor with excellent performance and complete function is an important subject.In view of the above problems,we prepared(PAA-PDA-Fe3+)double crosslinked reversible adhesive hydrogel,(PMEA-PAM-PDA)self-adhesive organic hydrogel at subzero conditions and(PVA-clay-PDA/P(NIPAM-co-AM))nano enhanced double network controllable adhesive hydrogels.A series of experiments have been carried out on the study of polymerization mechanism,the control of mechanical properties and the application of adhesion sensing.The specific contents include:(1)The PAA-PDA-Fe3+hydrogel is composed of a double bond modified Pluronic F127 two acrylate(F127DA)cross-linked polyacrylic acid(PAA)network and PDA,and is further cross-linked by Fe3+.PAA-PDA-Fe3+hydrogel has excellent self healing,reversible adhesion,mechanical stretching and electrical conductivity.The flexible sensor assembled by PAA-PDA-Fe3+hydrogel has the advantages of large sensing range(0-575%),high sensitivity(GF=6.31),fast response(0.25s)and sensing stability(>500 cycles).It can accurately monitor the large strain and small strain of joint movement and muscle movement.(2)PMEA-PAM-PDA hydrogels were prepared by the "split phase" method.Emulsion polymerization of hydrophobic monomer 2-methacrylic acid 2-methoxy ethyl ester(MEA)was carried out in F127DA micelle,and polymerization of acrylamide(AM)and polydopamine(PDA)was carried out in aqueous phase.Because the adhesive component of PDA is formed in the aqueous phase,and the free radical polymerization of hydrophobic monomer mainly occurs in the micelle phase,the inhibition of free radical polymerization process by PDA is reduced.The introduction of PDA in hydrogel greatly increased while maintaining a higher strength(>300kPa).The resistive sensor assembled by PMEA-PAM-PDA hydrogel has a large sensing range(0 to 430%)and a low response time(0.25s).Further,glycerol was used to prepare freeze drying and anti drying organic hydrogels.The sensor can meet the low-temperature adhesion characteristics at-20℃.It can be used as a wearable sensor to monitor various human sports and physiological activities..(3)PVA-clay-PDA/P(NIPAM-co-AM)hydrogels are polyvinyl alcohol intercalated montmorillonite nanoparticles(clay-PDA)cross-linked polyvinyl alcohol(PVA)(PVA-clay-PDA)as the first network,BIS cross-linked P(N-isopropylacrylamide acrylamide)P(NIPAM-co-AM)as the second network.The nano enhanced dual network hydrogel has high tensile strength(>600%)and high strength(>230kPa),temperature sensitivity and reversible adhesion to temperature control.Using PVA-clay-PDA/P(NIPAM-co-AM)hydrogel as a strain sensor,it has high sensitivity(GF=1.9),fast response(0.25s)and controllable adhesion(>5 cycles).It can be used for swallowing,chewing,finger bending and other human motion detection.