Response Surface Optimization And Force-induced Evolution Of Pore Structures In Microbially Fermented Hydrogels

In view of the fact that yeast is a facultative anaerobic fungus,which metabolizes CO₂under both aerobic and anaerobic conditions,human beings use it for fermentation to make food,such as bread and steamed bread.It can be seen that yeast is an excellent microbial foaming agent,which has the advantages of fast reproduction,diversified products,wide sources,low price,safety,environmental protection and other microorganisms.However,there are many factors influencing the preparation of porous hydrogels by yeast fermentation,and the internal relations among these factors are complex.In this study,the factors affecting the fermentation process and gelation process were screened by Single Factor Experiment,and the experimental scheme was designed by Response Surface Methodology（RSM）.The preparation process of yeast fermentation multi-stage porous gel was further optimized to determine the optimal experimental scheme.In addition,the evolution behavior of porous structure induced by yeast under tension was preliminarily analyzed.Firstly,poly（isopropylacrylamide）porous hydrogel was successfully prepared by free radical polymerization through yeast fermentation induction.The density,maximum swelling degree and compression strength test data were analyzed by single factor analysis.The results showed that the proportion of yeast/glucose,gelation temperature and gelation reaction time had the greatest influence on the preparation process.Secondly,Response Surface Methodology（RSM）was used to design the experimental scheme,and the preparation process of yeast fermentation porous hydrogel was further optimized to determine the optimal experimental scheme.The results showed that the optimal experimental conditions for preparation of porous gel by yeast fermentation were as follows:yeast/glucose ratio 2.0,the amount of monomer NIPAAm 2.5 g,the amount of crosslinking agent N,N’-methylene bisacrylamide（MBA）0.2 g,the gelation temperature of yeast fermentation 25 ^oC,and the gelation reaction time 240 min.Under the optimum conditions,the density of the porous hydrogel is 120.22 Kg/m³,the maximum swelling degree is 808.00%,and the compressive strength is 0.9560 MPa,which provides theoretical basis for the preparation and application of the porous hydrogel fermented by yeast.Thirdly,the morphology of porous hydrogels was compared by optical microscope,electron microscope,confocal microscope and X-ray microscope.According to Mercury Porosimeter test and density test,the porosity of sodium alginate/polyacrylamide（SA/PAAm）porous hydrogel prepared by yeast fermentation can be as high as 93%,and the density can be as low as 51.8 Kg/m³.It is also found that the prepared porous hydrogels exhibit different swelling degrees in different p H environments,and the swelling degree gradually increases with the increase of p H value.The analysis of sound absorption and noise reduction shows that the porous hydrogel has excellent sound absorption and noise reduction ability,and the sound absorption coefficient is as high as 0.973.Finally,the evolution behavior of multi-stage porous gel pore structure under dynamic tension was studied,and the variation laws of super-macroporous,macroporous and microporous morphologies and pore length-diameter ratio（R）under different tension ratios（ε）were comparatively analyzed.The results show that with the increase ofεfrom 0%to 100%,a large stress concentration occurs around the super-large hole firstly,which leads to the hole being rapidly stretched into an elongated elliptical shape,and the pore length-diameter ratio R_macincreases sharply to4.5.In contrast,the large pores deform only slightly during this process,and the aspect ratio R_micincreases slowly to 1.5.The pore structure of the multistage porous gel exhibited a regioselectivity under continuous stretching.