Optimization of monomethoxy-polyethylene glycol grafting on the pancreatic islet capsules

As a new approach to islet transplantation, biocompatible monomethoxy-poly(ethylene glycol) (mPEG) was chemically grafted onto the pancreatic islet capsule. The aim of this study was to determine the optimal conditions for completely covering the islet by the mPEG while maintaining a high viability of islets according to the reaction time and the repeating number of the reaction. By grafting the fluorescein-PEG instead of mPEG, we determined the optimal mPEG grafting time as 1 h, during which time the procedure did not reduce islet viability. Insulin secretion from islets where the mPEG was grafted on for 3 times was similar to that of control islets. Moreover, the mPEG-grafted islets rapidly responded to the changes in the glucose concentration in the same pattern as did control islets. These results showed that mPEG grafting did not damage the function of islets. In conclusion, when the mPEG grafting was performed for 1 h and repeated twice with 1-day culture between each mPEG-grafting step, the mPEG completely covered the islet capsules without any damage to the viability and function of the islets. The main advantage of mPEG grafting on the islet capsule is that it can protect the islet against the host's immune system without increasing the islet size so that it can be administered into the portal vein by the catheter.