Preparation Of Physically-physically Cross-linked Tough And Conductive Double-Network Hydrogel And Their Study In Strain Sensor

Conductive double-network hydrogels are flexible materials with excellent mechanical properties,good electrical conductivity,and strain sensitivity,which are favored by researchers in the fields of wearable sensors,human health monitoring,flexible robots,and nanogenerators.However,the development of conductive double-network hydrogels still faces problems such as lack of good adhesion and rapid self-recovery,inability to combine high mechanical strength and electrical conductivity,and poor biocompatibility.In view of the above deficiencies,this paper designed and synthesized two high-strength physically-physically cross-linked conductive double-network hydrogels(κ-CG-K⁺/p HEAA hydrogels and BSA-MA-PPy/P（AM-co-AA）/Fe³⁺hydrogels)and explored their practical application in flexible strain sensors.Specifically,the research content of this paper includes the following two aspects:（1）Preparation of physically-physically cross-linkedκ-CG-K⁺/p HEAA conductive double-network hydrogel and its research in strain sensorWithκ-carrageenan（κ-CG）as the first network and poly（N-hydroxyethyl acrylamide）as the second network,a high-strength and strong-adhesivephysical-physicalcrosslinkingconductiveκ-CG-K⁺/p HEAA double-network hydrogels was prepared by a one-pot method and assembled into strain sensors to monitor human activity.Under the optimal ratio conditions(m _CG=200 mg,C_K+=6 wt%,m _HEAA=5.0g),the prepared hydrogel had strong mechanical properties（the tensile strength of 2.02 MPa,tensile strain of 1181%,and elastic modulus of0.79 MPa）,excellent recovery and self-healing properties.Due to the abundant hydroxyl and amide groups in the network,the hydrogel exhibited excellent adhesion on various substrate surfaces,and its interfacial toughness on titanium plate reached 773 N/m².The addition of potassium ions not only improved the mechanical properties of the hydrogel,but also endowed the hydrogel with good electrical conductivity.In addition,the hydrogel flexible sensor displayed excellent strain sensing,sensitivity（GF=2.48）and stability,and can well detect the activities of different joints of the human body.（2）Strain sensors based on BSA-MA-PPy/P（AM-co-AA）/Fe³⁺conductive double network hydrogel for human motion and heart rate monitoringThe BSA-MA-PPy/P（AM-co-AA）/Fe³⁺double-network hydrogels with high-strength,rapid recovery,and conductive was synthesized by a polymerization-soaking two-step method using polypyrrole-modified bovine serum albumin as the first network and acrylamide-acrylic acid copolymer as the second network,and used it as a strain sensor and heart rate monitor electrode to monitor human motion and heartbeat.The hydrogel exhibited excellent mechanical properties（its tensile stress,compressive stress,elastic modulus,and toughness reached 5.36 MPa,39.01 MPa,3.13 MPa,and 17.66 MJ/m³,respectively）,rapid recovery（after 10 min resting,the mechanical properties of the hydrogels can be recovered to more than 93%）,and fatigue resistance.Bovine serum protein was used to construct the hydrogel network,which endowed the hydrogel with good biocompatibility.Due to the synergic conductive effect of free ions and polypyrrole,the hydrogels had good conductivity（0.99 S/m）and strain sensitivity（GF=4.6）,and the hydrogel strain sensors for monitoring human movement and compression deformation.In addition,the hydrogel can be used as a flexible electrode in a heart rate monitor to monitor human heart rate in real time.