Preparation And Properties Of Shape Memory Hydrogel Based Gelatin

Stimuli responsive polymer is a kind of materials which can response to external stimuli such as light,heat,sound,water,ion,chemical reaction and so on.The changes of physical and chemical properties such as change of the swelling degree,the change of hydrophilicity are generally made in response to the stimuli.The Mimosa in natural is a kind of stimuli responsive material.Shape memory hydrogel is a common class of stimuli responsive polymer,which can be temporarily fixed under external conditions and return to the original shape when stimulated by the corresponding stimuli.Because of its special performance such as nontoxicity and good biocompatibility,it has great potential in the field of biomedicine and attracted wide attention of researchers.However,the inevitable water absorption and swelling of the traditional hydrogel caused by affinity with water will reduce its mechanical properties.In recent years,some methods have contributed to solving these problems,such as dual network,nanocomposite,supramolecular hydrogel and so on.The construction of double network hydrogel is a common method to enhance the mechanical properties of hydrogel,but the response of the hydrogel is relatively simple.Therefore,the preparation of hydrogels with excellent mechanical properties and multi stimulus response based on dual network is of great significance.This research work is carried out in the following three parts:A double network hydrogel was prepared by free radical polymerization with acrylamide as a monomer,N,N’-methylene bisacrylamide as crosslinking agent,ammonium persulfate as initiator,gelatin as the physical crosslinker.The effects of component content on the mechanical properties and shape memory properties of hydrogels were investigated.When the concentration of（NH₄）₂SO₄ is 20 wt%,the shape memory property of hydrogel is the largest.When gelatin content is 8 w/v%,the shape memory property of hydrogel is the best.Double responsive double network hydrogels were prepared by free radical polymerization using acrylamide（AM）and acrylic acid（AA）as monomers,N,N’-methylene bisacrylamide as chemical crosslinker,ammonium persulfate（APS）as initiator,gelatin and graphite oxide（GO）as physical crosslinker.The effects of graphite oxide（GO）,acrylic acid（AA）and gelatin content on the mechanical properties of hydrogel were investigated.It is found that the carboxyl group（-COOH）of acrylic acid in the hydrogel can form the coordination crosslinking with the trivalent iron ion(Fe³⁺),and the reducing agent and chelating agent can destroy the coordination crosslinking,thus the hydrogel have shape memory properties,and the coordination crosslinking also enhances the mechanical properties of the hydrogel.In addition,the salting out effect（Hofmeister effect）of gelatin under brine condition can also make it have salt water responsiveness.Double network hydrogel were prepared by simple free radical polymerization using acrylamide（AM）as a monomer,N,N’-methylene bisacrylamide as crosslinker,ammonium persulfate（APS）as initiator,gelatin,polyvinyl alcohol（PVA）and graphite oxide（GO）as physical crosslinker.The effects of graphite oxide（GO）,polyvinyl alcohol（PVA）,gelatin content on the mechanical properties of hydrogels were investigated,and the effects of gelatin and other components on the shape memory properties were also investigated.It is found that the polyhydroxy of the polyvinyl alcohol（PVA）molecular chain can form a reversible covalent bond with four sodium borate,which not only enhance the mechanical properties of the hydrogel,but also make the hydrogel p H responsiveness,...