Design And Fabrication Of Hybrid Hydrogel Beads For Enzyme Immobilization Based On Biomimetic Silicification/Calcification

Biomimetic mineralization, which utilizes natural polymer or syntheticanalogues to catalyze the formation of inorganic oxides can be operated under mildconditions. The size and morphology of the inorganic materials can be controlled bythe template. Therefore, it has significant advantages in preparing organic-inorganichybrid materials. Based on biomineralization, choosing natural polymer materialswith the function of shape-forming and biomimetic mineralization such as gelatin andchitosan, the core–shell structure of organic-inorganic hybrid carriers were fabricatedby simple and effective method. These organic-inorganic carriers were utilized foryeast alcohol dehydrogenase(YADH) immobilization.The main details in this study were summarized as follows:Firstly, based on the gelling ability of gelatin at low temperature and inducingsilicification, choosing sodium silicate as precursor, the core–shell structure of thegelatin-silica beads were fabricated. Yeast alcohol dehydrogenase (YADH) wasencapsulated in the hybrid beads during the silicification process. The effects ofdifferent conditions such as pH, the concentration of sodium silicate andglutaraldehyde on biomimetic silicification were studied. The silica shell was uniformand complete coverage on the surface of the gelatin beads under optimized conditions.The as-prepared gelatin-silica hybrid beads displayed superior swelling resistancecompared to pure gelatin beads and enzyme leakage was notably reduced. Theencapsulated YADH exhibited significantly higher thermal stability, recycling stabilityand storage stability as well as a broader temperature range than its free counterpart.Secondly, based on the gelling ability of chitosan by ionic crosslinking andinducing calcification, choosing calcium chloride as precursor, the core–shellstructure of the calcium phosphate-mineralized chitosan beads (chitosan-CaP) wereprepared via a one-pot method. The chitosan beads formed immediately and coupledwith in situ precipitation of calcium phosphate. The effects of different concentrationsof calcium chloride on the morphology and swelling properties of hybrid chitosanbeads were studied. The anti-swelling properties of hybrid beads were greatlyimproved and the swelling degree decreased to5%. The immobilized YADHenhanced operational stability, thermal stability and storage stability compared withnative YADH counterpart. After storing for50days, the immobilized YADH stillremained80%of the initial activity. Thirdly, based on the gelling ability of chitosan and gelatin easily inducingsilicification, choosing sodium silicate as precursor, the core–shell structure of thechitosan/gelatin-silica beads were fabricated. YADH was then encapsulated in hybridbeads. The effects of different concentrations of sodium silicate on the morphologyand swelling properties of hybrid chitosan beads were studied. The anti-swellingproperties of hybrid beads were greatly improved and enzyme leakage was notablyreduced due to the silica shell. Compared to free YADH, encapsulated YADH showedenhanced stabilities. Especially, YADH encapsulated in the hybrid beads still retainedabove60%of its initial activity after8batches.