Study on membrane characteristics of alginate–chitosan microcapsule with cell growth

Alginate–chitosan (AC) microcapsule with polyelectrolyte complex (PEC) membrane has been attractive in biotechnological area such as cell immobilization fermentation. The PEC membrane has been known important to control microcapsule performance, but the knowledge was mainly obtained with empty or drug-loaded microcapsules. In this paper, the emphasis was to explore the influence of cell growth on PEC membrane characteristics, that is, to study the membrane characteristics in dynamic process. AC microcapsule entrapping yeast cells (Saccharomyces cerevisiae BY4741) was used as model, and the PEC membrane characteristics including membrane thickness, swelling behavior, permeability, and component were studied during cell culture process. It was found that both the membrane thickness and volume swelling degree of AC microcapsule increased, however, membrane permeability decreased with the growth of entrapped yeast cells. Fluorescence-labeling studies suggested the concentrated alginate layer squeezed by the proliferated cells and macromolecular metabolites layer secreted by proliferated cells contributed to above increment. The former PEC membrane, together with the new layers, constituted the ‘apparent membrane’, which increased the diffusion resistance of substances.