DEGRADABLE SCAFFOLDS FOR GENETICALLY ENGINEERED GRAFTS

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The goal of this proposal is the development of polymeric scaffolds for cardiovascular tissue engineering which will lead to the production of tissue-based small diameter vascular grafts. Hydrogel polymer scaffolds will be formed by rapid photopolymerization of aqueous precursors which allows for the incorporation of cell suspensions within the final product. Cell viability is maintained during this process, and the focus will be on the use of genetically engineered smooth muscle and endothelial cells. The incorporation of a variety of bioactive domains within the structure of the hydrogel matrices will be investigated to promote cell adhesion, growth, and extracellular matrix synthesis. Bioactive domains to be incorporated will include cell adhesion peptides and peptide growth factors. Cells will be transduced with genes that encode NO synthase for NO production (a proven anti-thrombotic agent), an endothelial cell-specific growth factor (VEGF), lysyl oxidase to enhance matrix crosslinking, and protease inhibitors (TIMPs) to reduce matrix degradation. In vitro assessment of cell viability and proliferation, extracellular matrix synthesis, and transgene expression will be performed under conditions of flow and static culture. Polymer preparations and polymer/cell composites will be tested using small animal in vivo vascular injury models for the recruitment of endothelial cells and the maintenance of homeostasis. Coating of Dacron grafts with polymers and polymer/cell composites will be investigated both in vitro and in vivo in canine arteriograft modalities. The ultimate focus of this proposal is to develop polymers which are biodegradable and can be used to support cell growth and deposition of extensive extracellular matrix material for de novo synthesis of vascular tissue. Populations of vascular cells (smooth muscle and endothelial cells) will be introduced as suspensions to the polymer environment prior to crosslinking of the hydrogel. Genetic engineering of cells will be used to optimize their production of matrix materials for the formation of tissue structures with mechanical integrity and to introduce anti- thrombotic properties to the newly formed tissue. The proposal seeks to develop vascular tissue grafts based on the provision of a biodegradable structure which will serve as a temporary scaffold and which will promote the proliferation and extracellular matrix elaboration of normal and genetically enhanced cell populations.