Deformable Hydrogel Sensing Actuator With Temperature-triggered Reversible Adhesio

In recent years,hydrogel sensing actuators have been widely used in artificial intelligence,biomedicine,software robots and other fields.Among them,self-powered sensors based on piezoelectric and frictional methods have received widespread attention from researchers due to their mechanical properties similar to skin and no need for additional power sources.However,these two sensors cannot record static and low-frequency pressures,and are different from the signal carriers(ions)of the human sensory system,limiting their application range.In addition,as a 3D deformable material,the self deformable hydrogel actuator has been prepared by researchers using 3D printing technology,but the current 3D printing technology is difficult to combine the microscopic anisotropic structure with the macroscopic complex deformation.Another important and unique element of hydrogel sensing actuators is the adjustable adhesion.However,conventional adhesives may have poor adhesion on soft surfaces,making it difficult to remove them after use,and cannot be reused after removal.Although researchers have designed and constructed reversible on-demand debonding adhesives,these adhesives need to achieve reversible adhesion under external stimuli such as ultraviolet radiation,current,specific separation fluids,etc.These stimuli may be difficult to achieve for human skin use.Therefore,in order to solve the above problems,this paper studies and designs a thermal responsive deformable hydrogel sensing actuator combining self-powered structure and adjustable adhesion capability.(1)In this paper,gradient polyelectrolyte hydrogels were prepared using dimethylaminoethyl methacrylate(DMAEAM)and N-isopropylacrylamide(NIPAM)as reaction monomers under unilateral UV irradiation.The final lowest phase transition temperature(LCST)of the hydrogel sensor is 33 ℃.When the temperature is higher than the LCST,the adhesion of the hydrogel sensor is enhanced,the transparency is reduced,and the mechanical performance is improved.When the temperature is lower than the LCST,the adhesion of the hydrogel sensor is reduced,easy to peel off,and the transparency is improved.The gradient polyelectrolyte hydrogel sensor has a self induced potential due to the free movement of its internal charge and the gradient structure of its aperture,and can sense the slight change of pressure.It has a high stress sensitivity,a wide strain sensing range,and a high strain sensitivity.In addition,the sensor can also sense the changes of human fingers,wrists and other joints for accurate detection,proving the potential application of hydrogel adhesive in artificial skin and self powered biomechanical monitoring system.(2)Based on the thermal response deformation behavior of poly(N-isopropylacrylamide)(PNIPAM)hydrogel,by adjusting the UV absorber,and using unilateral UV light to induce the hydrogel to generate gradient structure and non-uniform residual internal stress field,the hydrogel obtained spontaneously bends to the non light side after heating.Then,through the introduction of photomask,the local internal stress field of the hydrogel can be precisely adjusted to achieve deformation and bending,so as to realize the 3D complex deformation of the hydrogel,and build a 3D hydrogel "claw" to achieve the adhesion and grasping of objects of various shapes.