Fabrication And Actuating Behvior Research Of Gradient Porous Composite Hydrogel

Intelligent hydrogel actuators offer fascinating applications due to their unique structural forms that can produce specific shape changes under external stimuli such as light,electricity,heat,p H,magnetic and ionic strength.However,the lack of a simple and universal method for preparing anisotropic hydrogels with rapid response and recovery properties has hindered their further practical application.Although researchers have put forward some solutions,such as the preparation of anisotropicdouble hydrogels by stepwise polymerization method;using special chemical crosslinking agent or nanoparticles with the extra complex magnetic field or electric field to induce heterostructure;however,the hydrogels we have mentioned have complex preparation process,long experimental period,unstable interface and slower speed in bending and recovery.Therefore,the exploration of a simple,green and universal preparation method for obtaining heterogeneous hydrogels with the capacity of fast actuation,recovering,diverse deformation and easy functionalization is urgent and challengeable.This paper mainly focuses on the preparation of anisotropic hydrogels,the research of driving performance and design of actuating structure to obtain hydrogels actuator by the different liquid diffusion（such as amyl alcohol,water,ethanol,methanol and glycerol and aqueous solution containing functional nanoparticles（CNTs and Fe₃O₄））into monomeric precursor solution of hydrogels（such as polyisopropyl acrylamide（PNIPAM）,polyacrylic acid（PAAC）,and polyacrylamide（PAAM））.Monolayer anisotropic hydrogel actuators with excellent response performance are prepared by in-situ polymerization with extra solutions.And the research content of this paper mainly includes the following parts:1.Based on the principle of liquid delamination and interface diffusion,we studied and induced PNIPAM thermo-sensitive hydrogel driver by adding amyl alcohol on the hydrogel precursor solution.The response of hydrogel actuator is controlled by changing the diffusion time between amyl alcohol and NIAPAM hydrogel precursor solution,the content of amyl alcohol and the thickness of the hydrogel.In addition,various deformations of hydrogels from 2D to 3D could be achieved through different structural designs by using the mask.The results show that the actuator can get up to the maximum angle of 360°within 10 s when 1 m L amyl alcohol is added on the surface of the precursor solution with the 3min-diffusion time in hot water.At the same time,the patterned hydrogel can be achieve different angles of spiral like 30°,45°,60°,90°,and different digitals including"0","1","2","3","4","5","6","7","8","9"or other complex three-dimensional deformation（3D）.2.In order to explore the universal preperation method of hydrogel with the principle of liquid delamination and interface diffusion we have mentioned,we choose different inorganic solution such as water,ethanol,methanol and glycerol to add on the surface of NIPAM gel precursor,and take the same way to control their diffusion time.By scanning electron microscopy（SEM）observation,it can be confirmed that water,ethanol,methanol and glycerol also mutually diffuse with the precursor solution of NIPAM hydrogel and generate anisotropic structure.The obvious gradient difference makes the hydrogel actuator have better response performance.As a result,it is proved that the preparation method of the hydrogel is widely applicable,and these obvious gradient difference makes the PNIPAM hydrogel actuator have excellent response performance to temperature.3.In order to further validate the universality of the preparation methods and obtain functional hydrogels actuator,we choose different responsiveness hydergel precursor like AAM and AAC hydrogels precursor or aqueous solutions with different functional nanoparticles,such as carbon nanotubes（CNTs）and Fe₃O₄nanoparticles to prepare diverse functional hydrogel actuators with the rule we have proposed.Adopt the same method to add these solutions onto hydrogels precursor surface,and control the diffusion time of the added material on the hydrogel precursor to further control response and bending properties of the hydrogel.Furthermore,the anisotropic microstructure of hydrogel is confirmed by SEM.All in all,we proposed a simple,green,and fast strategy with one-step synthesis to prepare robust gradient porous hydrogel actuators.This hydrogel actuator can respond to temperature,light and magnetic.Therefore,this green,general and facile diffusion-driven strategy provides significant guidance for fabricating environmental responsive hydrogels with tailorable functionality for their multipurpose applications in drug delivery,bioengineering,smart actuator,and soft robot.