Tissue Engineering Scaffolds for Protein and DNA Delivery: A Platform for Islet TransplantationPublic Deposited
Tissue engineering offers a promising approach for the replacement of diseased or injured tissues, and is based upon the premise that cells can be induced to form new tissues when presented with the appropriate set of environmental cues. Polymer scaffolds play a central role in most tissue engineering strategies by providing a three-dimensional structure to support cell adhesion and organize tissue formation. However, the creation of controllable microenvironments capable of directing cellular behavior and coordinating the formation of complex tissues represents a significant challenge in the field of tissue engineering. To this end, controlled delivery of proteins and DNA from scaffolds can be used to manipulate soluble signals (e.g. growth factors) present within the local tissue microenvironment, and thereby regulate a variety of cellular processes such as migration, proliferation, and apoptosis. The primary objective of this dissertation was to develop scaffolds for DNA and protein delivery, in order to create an effective platform for islet transplantation, which is a cell-replacement therapy for the treatment of type I diabetes. DNA-releasing scaffolds were evaluated for their ability to provide localized and sustained transgene expression in vivo at different anatomical locations. Both the implant site and DNA dose were important factors that regulated the extent and duration of transgene expression. A critical limitation in the initial scaffold design was discovered in that the DNA incorporation efficiency was dependent on the scaffold structure. To eliminate this constraint, an alternative layered scaffold design was developed. Microcomputed tomography analysis demonstrated the ability of scaffolds delivering angiogenic proteins or DNA encoding angiogenic proteins to locally enhance vascularization, which will likely be important for promoting islet survival and function. Scaffolds were also developed for sustained delivery of exendin-4, a peptide that exhibits several therapeutic effects on islet cells. Initial studies have demonstrated that islets transplanted on exendin-4-releasing scaffolds exhibit enhanced function relative to those transplanted on control scaffolds. The continued development of scaffolds for controlled delivery of DNA and additional therapeutic proteins will likely lead to novel strategies for improving the outcome of islet transplantation.