Tissue-engineered pancreatic islets: culturing rat islets in the chitosan sponge.

Subcutaneous islet transplantation has become an attractive modality. With development of tissue-engineering techniques, it is possible to rectify the disadvantage of poor blood supply in the subcutaneous site by reconstruction of the capillary network. According to reports, the Chitosan sponge (CS) could be used for reconstruction of in vitro capillary-like network and could be used in artificial skin equivalent. In this study, we cultured the islets in CS for future application. CSs, having 200-500 microm pore size, were prepared by freeze-drying method. Rat islets were isolated from the pancreas of Lewis rats (10 weeks old, 280-300 g, male) by collagenase digestion followed by discontinuous dextran gradient centrifugation method. Each 20 islets were seeded equally into the CSs and were cultured for 62 days with various culture media such as RPMI-1640, Dulbecco's modified Eagle's medium (DMEM), and Eagle's MEM. They contained 10% fetal bovine serum (FBS) and 5 ml/L antibiotic-antimycotic mixed stock solution in the culture dishes. Insulin concentration both inside and outside of the islet-seeded CS was measured during culture. Changes in the morphology of islets were also observed in this study. Freshly isolated islets had a loose appearance with an irregular border, and most were seen as a single islet. Occasionally a cluster, consisting of 2-4 islets ranging mainly from 150 to 250 microm in diameter, was observed. Islets cultured in the CSs in different culture media retained initial morphology, which had well-delineated smooth borders for at least 53 days. The insulin release behavior of islets cultured in the CS showed constant secretory capacities for 49 days. After that they exhibited a rapid and definitive decline from the initial insulin release. Until this stage, insulin concentration in the CS was well maintained. The properties were dependent on culture medium used and insulin diffusion released from islets. This experiment is a new study model for establishment of islet culture in a three-dimensional matrix. Also extension of this observation will provide new insights for islet transplantation at the subcutaneous site by a tissue-engineering approach.