Cryopreservation and xenotransplantation studies of microencapsulated rat pancreatic islets

Islets of Langerhans were isolated from the Sprague Dawley rat pancreas digested by injected collagenase, and purified by Ficoll density gradient centrifugation. In order to make smaller and more uniform microencapsulated islets, we designed a special high-voltage electrostatic microcapsule generator. The effects of operational parameters of the generator on the size and the uniformity of microcapsules were analyzed, such as the voltage, the plunger speed of suspension delivery to the needle tip, the distance between needle tip and solution surface. The optimal parameter combinations for making microcapsules are: 5 kV of voltage, 50 mm/h of the plunger speed, and 20 mm distance. The high-voltage electric system can produce uniform microcapsules with diameters ranging from 0.3 to approximately 0.5 mm, which are smaller and more uniform than those produced by air-jet system. A comparison of the cryopreservation effects between microencapsulated islets and unencapsulated islets showed that the microcapsules can protect the fragile islets from freezing damage, and increase the retrieval rate from 68.5% to 92.6%. Xenotransplantation of the cryopreserved rat islets resulted in the normalization of the metabolic blood glucose of the diabetic mice for 90 days, whereas the unencapsulated islets were easily fragmented and lost during the freezing process. They only reversed hyperglycemia for less than 3-5 days.