Improvements in biomedical devices have increased the overall success rates of islet transplantation for diabetics, as noted in the January issue of Cell Transplantation (Vol. 17 No.9).

A review by Dr. Cherie Stabler and colleagues from the Diabetes Research Institute and the Department of Biomedical Engineering at the University of Miami, evaluated the engineering of bio-hybrid devices and encapsulation technologies that may aid in the success of islet transplants.

"A recent focus has been to redesign bio-hybrid devices that promote vascularization and effective nutrient delivery to prevent islet cell necrosis and at the same time minimize device volumes," said Stabler.
According to Stabler, one bio-hybrid design has been fabricated for pre-vascularization to afford maximum nutrient delivery and minimal exposure to inflammatory agents. At the same time, macrodevices, such as hollow fibers, have also been used for cell loading.

"The combination of these two treatments increased vascularization and blood flow around a bioartificial pancreas when compared to control implants," noted Stabler.

Encapsulation is also a technique for minimizing both immune response and the need for high dose immunosuppressive protocols. By coating the surface of the cell with semi-permeable biomaterial, the ability of host cells to recognize surface antigens on implanted cells is impaired and provides a barrier between the host and transplanted cells. Masking immune recognition also opens the possibility for xenotransplantation.

"Biomaterials used for encapsulation should be well-characterized, pharmaceutical grade and verified as pyrogen and endotoxin-free," explained Stabler. "It is critical to establish guidelines for generating capsules optimized for biocompatibility, immunoprotection and islet function."

Researchers supported the use of the portal vein as a site for islet transplantation, but noted that there are issues with injecting encapsulated cells into the liver. Finally, the research team suggested decreasing capsule size to nano-scale and combining PEGylation coating of capsules with a layer of poly(ethylene) glycol molecules with low-dose immunosuppression to improve engraftment and long-term function.

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