A method has been defined to interfacially photopolymerize poly(ethylene glycol) diacrylates (PEG diacrylates) to form a crosslinked hydrogel membrane upon the surfaces of porcine islets of Langerhans to serve as an immune barrier for allo‐ and xenotransplantation. A sensitivity study of six key parameters in the interfacial photopolymerization process was performed to aid in determination of the optimal encapsulation conditions, leading to the most uniform hydrogel membranes and viable islets. The key parameters included the concentrations of the components of the initiation scheme, namely eosin Y, triethanolamine, and 1‐vinyl 2‐pyrrolidinone. Other parameters investigated included the duration and flux of laser irradiation and the PEG diacrylate molecular weight. Each parameter was doubled and halved from the standard conditions used in the encapsulation process while holding all the remaining parameters at the standard conditions. The effects of changing each parameter on islet viability, encapsulation efficiency, and gel thickness were quantified. Islet viability was sensitive to the duration of laser illumination, viability significantly increasing as the duration was reduced. Encapsulation efficiency was sensitive to the concentrations of eosin Y, triethanolamine, and 1‐vinyl 2‐pyrrolidinone, to the laser flux, and to the PEG diacrylate molecular weight. Increasing the concentration of eosin Y significantly improved the encapsulation efficiency, while decreasing the concentration of 1‐vinyl 2‐pyrrolidinone and increasing the concentration of triethanolamine had the greatest effects in significantly reducing the encapsulation efficiency. Gel thickness was sensitive to the concentrations of triethanolamine and 1‐vinyl 2‐pyrrolidinone, to the duration of laser illumination, and to the PEG diacrylate molecular weight. Increasing the PEG diacrylate molecular weight significantly increased the gel thickness, while decreasing the concentration of 1‐vinyl 2‐pyrrolidinone and increasing the concentration of triethanolamine had the greatest effects in significantly reducing the gel thickness. From this sensitivity study, conditions were determined to encapsulate porcine islets, resulting in greater than 90% islet viability and greater than 90% encapsulation efficiency. © 1998 John Wiley & Sons, Inc. Biotechnol Bioeng 57: 655–665, 1998

The usefulness of interfacial photopolymerization of poly(ethylene glycol) (PEG) diacrylate at a variety of concentrations and molecular weights to form hydrogel membranes for encapsulating porcine islets of Langerhans was investigated. The results from this study show in vitro and in vivo function of PEG-encapsulated porcine islets and the ability of PEG membranes to prevent immune rejection in a discordant xenograft model. Encapsulated islets demonstrated an average viability of 85% during the first week after encapsulation, slightly but significantly lower than unencapsulated controls. Encapsulated porcine islets were shown to be glucose responsive using static glucose stimulation and perifusion assays. Higher rates of insulin release were observed for porcine islets encapsulated in lower concentrations of PEG diacrylate (10-13%), not significantly reduced relative to unencapsulated controls, than were observed in islets encapsulated in higher concentrations (25%) of PEG diacrylate. Perifusion results showed biphasic insulin release from encapsulated islets in response to glucose stimulation. Streptozotocin-induced diabetic athymic mice maintained normoglycemia for up to 110 days after the implantation of 5,000-8,000 encapsulated porcine islet equivalents into the peritoneal cavity. Normoglycemia was also confirmed in these animals using glucose tolerance tests. PEG diacrylate-encapsulated porcine islets were shown to be viable and contain insulin after 30 days in the peritoneal cavity of Sprague-Dawley rats, a discordant xenograft model. From these studies, we conclude that PEG diacrylate encapsulation of porcine islets by interfacial photopolymerization shows promise for use as a method of xenoprotection toward a bioartificial endocrine pancreas.

The goal of islet transplantation in human diabetes is to maintain the islet grafts in the recipients without the use of immunosuppression. One approach is to encapsulate the donor islets in permselective membranes. Hollow fibers fabricated from an acrylic copolymer were used to encapsulate small numbers of rat islets that were immobilized in an alginate hydrogel for transplantation in diabetic mice. The fibers were biocompatible, prevented rejection, and maintained normoglycemia when transplanted intraperitoneally; hyperglycemia returned when the fibers were removed at 60 days. Normoglycemia was also maintained by subcutaneous implants that had an appropriately constructed outer surface on the fibers.

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The purpose of this study was to determine the in vitro effect of ovine PRL (oPRL) on the dynamics of insulin secretion and dye coupling among islet B cells. The effect of oPRL (2 micrograms/ml) on insulin secretion was time dependent and reached a maximum on day 4 when there was a 2.4-fold increase in insulin secretion from cultured neonatal rat islets (n = 6, P less than 0.001). When islets cultured in the presence of oPRL for 4 days were perifused, 300 mg/dl glucose stimulation resulted in insulin release of 131 +/- 20 microU/ml.100 micrograms islet tissue as compared to control islets 94 +/- 20 microU/ml.100 micrograms islet tissue (n = 7, P less than 0.02). Stimulation of the islets with a linear 30-250 mg/dl glucose gradient resulted in a threshold for glucose-stimulated insulin secretion of 73 +/- 6 mg/dl glucose for the oPRL treated islets (n = 7) as compared to a threshold of 123 +/- 6 mg/dl glucose for control islets (n = 7, P less than 0.001). Mean islet volume was unchanged after 4 days of oPRL treatment but was 34% greater after 8 days (n = 6, P less than 0.001). Dye coupling among central islet B cells was also increased after in vitro treatment with oPRL for 4 days. The mean projected area of dye spread was 2-fold greater in the oPRL treated islets (n = 33) in comparison to the control islets (n = 33, P less than 0.05). These results indicate that in vitro lactogen treatment, in the form of oPRL, alters insulin secretory behavior and B cell junctional communication and supports our hypothesis that lactogen, insulin secretion, and junctional communication among B cells are related.