Construction Of Thermoplastic Tough PNAGA Hydrogel And The Research Of Its Mixtures For Strain Sensors And Shape Memory Materials

Tough hydrogels that can be processed into various shapes repeatedly as thermoplastics have great practical significance.Until now,the re-processable hydrogels are general suffering from poor mechanical properties.What's more,these gels are usually based on shape memory effect,which cannot be shaped to arbitrary forms.In principle,physically cross-linked network by reversible bonds(hydrogen bonds,ionic bonds,hydrophobic interaction etc.)can endow hydrogels with re-processability.Therefore,in this paper double hydrogen bond cross-linking network was chose to construct a re-processable tough hydrogel and functionally modified with Li Cl and gelatin.First,we fabricated a class of supramolecular hydrogels with a network cross-linked by double hydrogen bonds provided by poly(N-acryloyl glycinamide)(PNAGA).The resulting PNAGA-30 hydrogels(the solid content of the hydrogel is 30%)were re-processable,tough(tensile strength up to 1.35MPa)and recyclable similar to thermoplastics.Meanwhile,PNAGA-30 hydrogel fragments could be reprocessed into various shapes,such as flakes,filaments,cylinders,or other complex shapes,by stamping in high pressure reactors or injecting after heating in a microwave oven.The mechanical properties of such reprogramed samples were comparable to the original samples.PNAGA hydrogels with re-processability and robust mechanical properties are promising for practical applications in the soft actuator,robot,wearable devices and load-bearing materials.Secondly,we further demonstrated the mixture PNAGA-30&Li Cl hydrogels and its applications.The resulting hydrogels also showed thermoplasticity and excellent toughness.In particular,the recovering efficiency of PNAGA-30&Li Cl hydrogels in tensile strength and conductivity was both approaching 97%,which could extend the service life of the materials.Furthermore,the repaired and reshaped hydrogels still maintained unique signal transmission capability comparable to the original state.The PNAGA-30&Li Cl hydrogels were fabricated into multifunctional strain sensors for monitoring physiological activities of the human body including large human movements(knee,neck,elbows,fingers,etc.)and tiny vibrations such as pulse beat,which could be found potential applications in robotics,biomedical prosthetics,personal healthcare monitoring,etc.Finally,a thermoplastic and tough shape memory hydrogel PNAGA-30 & Gelatin was prepared by compounding PNAGA-30 hydrogels with gelatin.The PNAGA-30&Gelatin hydrogels exhibited shape memory ability that responded quickly to temperature and redefinable permanent shapes.The gelatin network in PNAGA-30&Gelatin hydrogels would be softened at 37?,which enabled the hydrogel to write temporary shapes.When the temperature was further increased,the PNAGA-30&Gelatin hydrogel underwent a gel-sol transition,which enabled the hydrogel to redefine permanent shapes.Moreover,PNAGA-30&Gelatin had excellent mechanical properties(tensile strength?1.49 MPa,strain at break ?400%),which were pivotal for the applications of shape memory hydrogels for tumor embolization,deep tissue hemostasis,intelligent response,etc.