Immunoisolation of porcine islets of langerhans by polyurethane-silicone macrocapsules

The immunological problems related to islets tranplantation may be overcome by the immunoisolation of the graft, using micro- or macro-capsules. In botih cases it is mandatory for the capsules to be biocompatible, ìmpermeable to the immnunocompetent cells and freely permeable to nutrients and hormones. We prepared macrocapsules using as biomaterial a blend of polyurethanes and silicone. The macrocapsules were obtained by plugging segments of tubes prepared by a sprayilg and phase inversion technique that produced a microporus structure, with a thin skin on the inside of the tube. The rnacrocapsules were evaluated as for permeability to glucose, insulin, albunin, inrnunoglobulines and white blood cells. In addition, the response to glucose of macroencapsulatecl islets of Langerìrans purified fron the adult pig pancreas was studied. Glucose and insulin diffusion from the macrocapsules to the incubation mediun reached the plateau after 10 and 30 rninutes respectively. Albumin, immunoglobulines and blood white cells remained inside the macrocapsules. Macroencapsulated porcine islets secreted 3.7 +- 1.6 and 5.3 +- 1.4 uU insulin/islet/min (P< O.O5) in the presence respectively of 50 and 40 mg/dl glucose in KRBGB solution at 37 "C. The average increase of ormoone release was 55% at the higher glucose concentration, a value sirnilar to that one (60%) observed for freschly prepared, not encapsulated pig islets incuba'Ced at the same conditions. These results suggest the possibility of using poly-urethane-silicone macrocapsules for allo- and xeno-transplantations of islets of Langerhans.