The Fabrication And Performance Research Of Shape Memory Hydrogels Capable Of Intelligent Deformation

As an important smart polymer hydrogel,shape memory hydrogels(SMHs)can stabilize temporary shape and recover to permanent shape in respond to external stimuli,showing promising potential applications in biomedicine,soft robots.However,the development of SMHs is limited by precondition of manual intervention to endow temporary shapes.In recent years,hydrogels capable of shape changing emerged in endlessly.Not only simple swelling/shrinking,elongation/contraction can be made,but advanced movement such as self-working,shape-morphing can be achieved.If the mechanism of shape changing is introduced into shape memory hydrogels,the development of shape memory hydrogels will be promoted to a more intelligent,more practical direction.This thesis did follow works concerning the fabrication of SMHs capable of shape changing intelligently:1.In the thesis,a well-developed stimulus responsive polymer Poly(N-isopropyl acrylamide)(PNIPAAm)was utilized.Through layer by layer polymerization,PNIPAAm hydrogel was combined with chitosan(CS)shape memory hydrogel.As driven layer,the PNIPAAm hydrogel transfers from hydrophilic to hydrophobic in respond to temperature increasing.Intelligent deformation of the hybrid hydrogel can be made by changing temperature.In addition,due to the pH stimulus responsiveness of CS,microcrystal will be generated inside the hydrogel in respond to alkali condition,which acts as crosslinks to stabilize the temporary shape of our hybrid hydrogel,achieving shape memory functionality.By adjusting the thickness ratio of two layers,intelligent deformation and shape memory capacity of bilayer hydrogel can be adjusted.By using photo mask method,a patterned driven hydrogel layer was polymerized on the surface of the composite hydrogel.Through changing the type and morphology of the pattern,complex temporary shape of SMHs can be achieved.Stripe patterned PNIPAAm hydrogel was fabricated on the surface of CS hydrogel,enabling the transformation from plane rectangle to cylinder,from triangle sheet to quasi-cone,from strip to helix.The sinistrogyration and dextrorotation of the helix can be chosen by changing the angle of the stripe pattern.The deformation of localized patterned composite hydrogel is highly programmable.The shape fixity ratio is above 90%.2.Via using temperature responsive bio-macromolecule gelatin and fabricating the double network of chemical and physical crosslinks,we increased the mechanical strength of SMHs and achieved shape memory functionality simultaneously.The hydrogel prepared can be stretched to 4-5 times long to initial length.The maximum tensile stress of our hybrid hydrogel increased from 0.03 MPa to 0.3 MPa.After frozen in 2 ~oC,the hydrogel can memorize its temporary shape.The shape fixity ratio is above80%.The hydrogel can rapidly return to its initial shape after increasing the temperature to 90 ~oC.The shape recovery ratio is 100%.Taking advantage of different swelling behavior of poly(acrylic acid)in different pH,the deformation of SMHs can be adjusted,enabling shape memory and shape changing in respond to pH and temperature respectively.