Application Of Microbial Tissue Engineering In Biocatalysis

The immobilized cells can be protected from harsh environmentalconditions such as pH, temperature, organic solvent, and poison.Immobilized microbial cells also can be handled more easily and recoveredfrom the solution without difficulty. Nevertheless, the small void space ofpolymer matrix and the leakage of cells limit a final cell loading in the beadsof the traditional immobilization methods. In order toovercome the defects of the traditional immobilization methods, thescaffold of microbial tissue engineering is used as the immobilized catalyst.Polyvinyl alcohol （PVA） and Calcium alginate （ALG-Ca） were used as thescaffold material and cultured with Saccharomyces cerevisiae cells in it.,respectively. The two kinds of loading cells scaffolds were coated withnanocomposite gel of PVA/organic montmorillonite（OMMT）, and twodifferent scaffolds of microbial tissue engineering. The characteristics of thetwo kind of composite scaffolds and the properties of these two coatedcell-scaffolds were investigated in this article, respectively. In this paper,ethanol was prepared by the two coated cell-scaffolds as biocatalyst.Incidentally, the reusability and storage stability of the two coated cell-scaffolds have been investigated.Firstly, the cylinder shape three-dimensional porous scaffolds（4mmdiameter,2mm thickness） were prepared with PVA/MMT composites afterthe freezing process and salt-leaching, and its porosity reached71%. thedisk shape three-dimensional porous scaffolds（8mm diameter,2mmthickness） were prepared with ALG/MMT composites after theion-exchange process and paraffn-leaching, and its porosity reached93%.The expansion coefficient of PVA scaffold is0while ALG scaffold is1.18.All of them were easily operated suitable for cells culture, and more,significant effects are achieved after the diffusion research.Secondly, these two kinds of scaffolds as carriers for seeding ofSaccharomyces cerevisiae were cultured. Then the cell-scaffold compositeswere coated with about200μm thickness PVA/OMMT nanocomposite gel.After crosslinked using boric acid and sodium sulfate, the coated microbialtissue engineering scaffolds are prepared. We investigated embeddingsituation, cells load of the two coated microbial tissue engineering scaffolds,effects of pH and temperature on intracellular ADH activity of the coatedmicrobial tissue engineering scaffolds and storage stability of them. Theexperimental results indicate that the cells load capacity of the PVA scaffoldsreach to32mg cell d.w. cm^-3gel while ALG scaffolds reach to45mg celld.w. cm^-3gel and all of them have no cells leakage aftercoating（200³00μm）. Regardless of pH or temperature, the tolerance ability of the cells in coated microbial tissue engineering scaffolds have beensignificantly improved compared with the dissociated cells. And theintracellular ADH in the coated scaffolds retained over75.4%of it originalactivity after one month of storage.Finally, the production of ethanol is prepared with the PVA/MMTmicrobial tissue engineering scaffolds as biocatalyst. To examine itsreusability after the used scaffolds is recultivated, and the ADHactivity can be quickly restored with the range between98%to101%.