Synthesis And Characterization Of A Novel Hydrogel Based On Polysaccharide Isolated From Umbilicaria Esculenta Cultivated In Huangshan Mountain

Umbilicaria esculenta（Miyoshi）Minks,a complex formed by the symbiosis of fungi and algae,belong to the genus Lithocarpus.Huangshan Stone Ear Polysaccharide（HSSE）is a polysaccharide component prepared from Huangshan stone ear.In this paper,polysaccharide hydrogels were constructed using epichlorohydrin（ECH）as a cross-linking agent in polysaccharide HSSE/sodium hydroxide/urea system,and temperature-sensitive hydrogels were prepared on the basis of polysaccharide hydrogels,so as to clarify the physical and chemical properties of these hydrogels and expand the application scope of polysaccharide HSSE in the field of biological materials.The experimental results are as follows:（1）The effects of the ratio of sodium hydroxide to urea and the temperature on the stability of polysaccharide HSSE solution was studied by means of macromolecule method.The system mainly composed of a monodisperse inclusion compound,and the solution was the most stable,providing a stable polysaccharide solvent for the later hydrogel construction.（2）In the sodium hydroxide/urea water system,epichlorohydrin was introduced as a crosslinking agent to prepare a polysaccharide HSSE hydrogel.The rheological results showed that:the solution-gel transition of the polysaccharide HSSE/epichlorohydrin system is a function of HSSE concentration,epichlorohydrin content,and temperature.The concentration of polysaccharide HSSE in the system increased from 8 wt%to 12wt%,and the gel point decreased from 28 min to 22 min.The epichlorohydrin content increased from 10%to 14%and the gel point was shortened from 36 min to 22 min.An increase in temperature shortens the gelation time of the system.The results of FT-IR showed that the characteristic absorption peaks of polysaccharides in polysaccharide HSSE hydrogel were 3400 cm^-11 and 2900 cm^-1,respectively;the characteristic absorption peaks of epichlorohydrin were 1460 cm^-11 and 856 cm^-1,respectively.The appearance of characteristic peaks proved that polysaccharide HSSE and epichlorohydrin existed in the gel system,and the entire network structure had been successfully constructed.The SEM results showed that the hydrogel has a porous structure with a pore size ranging from 6 to 50μm.An increase in the concentration of the polysaccharide HSSE and the crosslinker resulted in a decrease in the pore size.The swelling results showed that the polysaccharide concentration increased from 8 wt%to14 wt%,the swelling rate of the hydrogel decreased from 17.7 g/g to 9.7 g/g;the crosslinker content increased from 10 v/v%to 14 v/v%,the hydrogel swelling rate decreased from 15.3 g/g to 10.3 g/g.The water retention capacity of the polysaccharide HSSE hydrogel increased with the increase of polysaccharide and epichlorohydrin content.Extracellular toxicity experiments demonstrated that polysaccharide HSSE hydrogels have no cytotoxic effects.（3）Based on the polysaccharide HSSE hydrogel,a temperature-sensitive hydrogel（IPN）was prepared by introducing poly（N-isopropylacrylamide）（PNIPAAm）.The SEM results showed that the IPN hydrogel has a tighter three-dimensional network and a uniform porous structure.The results of FT-IR and TGA showed that the first layer network and the second layer network are independent of each other,and there is a strong hydrogen bond between them,but no new chemical bonds are formed.DSC and swelling results showed that the lower critical solution temperature（LCST）of IPN hydrogel appeared near 32°C,when the temperature was higher than LCST,the IPN hydrogel contracted rapidly and the swelling rate decreased significantly,showing a typical temperature sensitivity curve.The vitro release behavior of bovine serum albumin as a model drug showed that the drug release rate and release amount increased with the increase of PNIPAAm content in IPN hydrogel,and the maximum release amount was 91.5%.When the temperature at 37°C（above LCST）,the drug release rate was constant,and at 32°C（below LCST）,the IPN hydrogel showed a burst release.Extracellular toxicity experiments have demonstrated that IPN hydrogels are non-cytotoxic and exhibit good biocompatibility.