Shape Memory Polyampholyte Hydrogels And Their Applications In Spontaneous Actuation

Usually shape memory hydrogels(SMHs)consist of two crosslinking nteworks: one is permanent crosslinked network to maintain the original shape of the hydrogel;the other one is temporary reversible crosslinked network,which can be constrsucted or destroyed under proper conditions.Therefore,SMHs can memorize the temporary shape under a stimulus and recover to the original shape driven by entropy elasticity of permanent network under another corresponding stimulus.The reversible network of SMHs can be established by supramolecular interactions or dynamic covalent and shape memory effect will be induced by different environmental stimuli based on different reversible interactions inside.SMHs are a very important kind of stimuli-responsive hydrogels and it's applied in biomedical more and more widely as a smart material.In the current work,we synthezed pH-induced shape memory hydrogel by introducing weak electrolytic monomers into the traditional polyampholyte hydrogels.Also,we prepared a thermal responsive shape memory hydrogel based on elastinlike polypeptide(ELP).First,we replaced part of strong anionic electrolytic monomer sodium p-styrenesulfonate(NaSS)with methacrylic acid(MAA)and the pH-induced shape memory polyampholyte hydrogel was synthesized by one-step copolymerization.The hydrogel didn't only have shape memory effect,but also spontaneous actuating by simply alternating HCl and NaOH solutions,which provided a new strategy for designing soft actuators with continuous movement.Then strong cationic electrolytic monomer [3-(methacryloylamino)propyl]trimethylammonium chloride(MPTC)was replaced with 2-(dimethylamino)ethyl methacrylate(DEAEMA)and another shape memory hydrogel was synthesized using a similar method.The hydrogel combined the excellent and stable shape memory with self-healing,self-reinforcement,conductivity,which would play an important role in the field of biomimic and biomedical.Additionally,we synthesized pH-induced shape memory polyion-complex(PIC)hydrogel by one-step polymerization,that was,2-(diethylamino)ethyl methacrylate(DEAEMA)was polymerized in presence of poly(styrene sulfonic acid)(PSSA)and NaCl.The hydrogel possessed good shape memory effect and the temporary shape could be helical shape or tensile state.The hydrogel also had self-healing property and several functions(wrapping,connecting and information encryption)were realized when combining swelling/deswelling property,which would be very valuable for smart materials.ELP is monodisperse polymer with high designability and biocompatibility.In this work a thermosensitivity hydrogel was synthesized using a long chain ELP(V250)and acrylamide.The hydrogel had shape memory effect and the process could repeat at least 10 times.Taking advantage of shape recovery during shape memory process,gripping an object and connecting two tubes were realized,which would open a new field to design biomedical materials.