Nutritional requirements of islets are not fully understood. It is certain that many small molecules are consumed fairly rapidly and must be freely available. It is also known that some larger molecules are necessary, but these larger molecules are not consumed at the same high rate. Thus, it is sufficient if these large molecules diffuse slowly through the device.

It is clear from a variety of studies that under most conditions, at least in the short term, the limiting nutrient is oxygen.

(figure courtesy Clark Colton, M.I.T.; Colton, C. K. (1995) Cell Transplant 4, 415-436.)

One cannot predict the exact permeability profile that will minimally satisfy the long-term nutritional requirements of coated islets. Islet Sheet Medical can address this tricky question empirically by simple and straightforward experiments. Using well-understood chemistry, we have demonstrated tight regulation of the molecular permeability of the alginate matrix surrounding and protecting the islets in Islet Sheets. In fact, it is possible to fabricate an Islet Sheet that is freely permeable to even the largest nutrients thought to be required for long-term islet function.