Interfacial photopolymerization of beta-cell clusters: Approaches to reduce coating thickness using ionic and lipophilic dyes

Microencapsulation of insulin-secreting cells is a potential therapy for Ty pe I diabetes. Critical requirements for therapeutic use are the high numbe r of beta -cells to be implanted and a fast insulin diffusion through the e ncapsulating membrane. The use of thin, conformal coating for beta -cell en capsulation may be a way to reach these goals by decreasing the capsule voi d volume. This study focuses on the production of very thin membranes by in terfacial photopolymerization of beta -cell clusters. Two types of photosen sitizing dyes were used: Eosin Y, which stains the cell surface as well as the cytoplasm, and a lipophilic-derivatized eosin that specifically stains the cell membrane. The fraction of encapsulated clusters and membrane thick ness were studied as a function of irradiation parameters. In the case of E osin Y, the fraction of encapsulated clusters is found to depend mainly on an optimal light dose for and above which complete encapsulation is obtaine d. We found that the membrane thickness decreased with decreasing irradiati on time, but does not depend on irradiation intensity. Using Eosin Y, 16 mu m thick coatings were obtained, together with a high fraction of encapsulat ed clusters. The coating thickness was further reduced to 10 mum by using t he lipophilic-derivatized eosin photoinitiator. Cell viability and function ality were studied following the encapsulation process using vital staining and measurement of insulin secretion. Cell viability and functionality wer e preserved following the encapsulation process with Eosin Y and for suffic iently low lipophilic dye concentration. Although it still requires further improvement, the method proposed here provides a promising route to obtain thinner coatings, down to a few microns. (C) 2001 John Wiley & Sons. inc.