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Melanie Köllmer. 1 Department of Biomedical Engineering, Illinois Institute of Technology, Chicago, Illinois.
Alyssa A. Appel. 1 Department of Biomedical Engineering, Illinois Institute of Technology, Chicago, Illinois. 2 Research Service, Hines Veterans Administration Hospital, Hines, Illinois.
Sami I. Somo. 1 Department of Biomedical Engineering, Illinois Institute of Technology, Chicago, Illinois. 2 Research Service, Hines Veterans Administration Hospital, Hines, Illinois.
Eric M. Brey. 1 Department of Biomedical Engineering, Illinois Institute of Technology, Chicago, Illinois. 2 Research Service, Hines Veterans Administration Hospital, Hines, Illinois.
Address correspondence to: Eric M. Brey, PhD, Department of Biomedical Engineering, Illinois Institute of Technology, 3255 South Dearborn Street, Chicago, IL 60616, E-mail: brey@iit.edu
Introduction
Transplantation of encapsulated living cells is a promising approach for the treatment of a wide variety of diseases. During cell encapsulation, viable cells are suspended in a biomaterial designed to serve as a transport barrier, allowing nutrients and oxygen to diffuse in and waste products to diffuse out while providing a barrier to larger objects such as antibodies and immune cells. This concept can be utilized to prevent graft rejection of nonautologous cell transplants and has been studied extensively for the delivery of islets as a treatment for type 1 diabetes. Islet transplantation is being evaluated as a therapy for some patients whose blood glucose levels are difficult to control, despite intensive insulin therapy.1 The goal of this procedure is to achieve normal blood glucose levels and to reduce or ultimately eliminate the need for daily insulin injections that are associated with the risk of hypoglycemic shock. Furthermore, long-term complications such as retinopathy, neuropathy, nephropathy, and cardiovascular problems could be prevented through reduction in hyperglycemic events.
Microencapsulation has been shown to result in prolonged survival and function of islet grafts in chemically induced and autoimmune diabetic animal models (rodents, dogs, and monkeys).2-4 However, different results with regard to the length of graft survival and overall metabolic benefits have been reported. Differences in study outcomes are difficult to interpret as they might arise from the use of different capsule materials/conditions, islet sources (allogeneic vs. xenogeneic), implantation sites, and recipients (normal vs. autoimmune).
A variety of synthetic and natural biomaterials have been explored for cell encapsulation. The most investigated material for islet encapsulation is alginate, which has...