Development of porous membranes of poly (lactic acid) via thermally induced phase separation and its application to bioprocesses

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Biodegradable polyesters, e.g., poly(_L-lactic acid), which are degraded by microorganisms in natural environment and degradable in human bodies, have recently received increased attention in bioengineering. In this study we have developed microporous membranes of biodegradable polyesters via thermally induced phase separation. At first effect of characteristics of polymers and conditions of phase separation (diluent, polymer concentration, and thermal history) on the growth of the droplet in phase separation and the structures and pore sizes of the formed porous materials. Then, we made microporous membranes of poly(_L-lactic acid), poly(ε-caprolactone), and their blends. The poly(_L-lactic acid) membrane showed the characteristics of a screen filter in the filtration of yeast cell suspensions. The membrane of a polymer blend of poly(_L-lactic acid) and poly(ε-caprolactone) showed that of a depth filter. The filtration flux with the latter membrane was much higher than that with the former. We also applied poly(_L-lactic acid) membrane to the production of an oxidase, laccase, by membrane-surface liquid culture of white rot fungus, Trametes versicolor. The membrane was stable at 28℃ and the fungus grown on the membrane secreted much more enzyme in the repeated use of membrane-surface liquid culture than in liquid surface culture. The porous biodegradable membranes would contribute to the development of sustainable bioindustry and biomedical engineering.