Development of 3-D collagen gel vascularized tissue-engineered constructs for bone replacement and regeneration using embryonic and postnatal progenitors

Adult stem cell based tissue engineering for repair and regenerative purposes, has been an emerging area of intense investigation. The current major challenge to these approaches has been the inability to vascularize and perfuse in vitro engineered tissue constructs. Attempts to provide oxygen and nutrients to cells contained in biomaterial constructs have met with varying degrees of success. Engineering a tissue of clinically relevant magnitude requires the formation of extensive and stable microvascular networks within the tissue. Since most in vitro engineered tissue constructs do not contain the intricate microvascular structures of native tissue, the cells contained in scaffolds heavily rely on simple diffusion for oxygenation and nutritional delivery. The majority of cells need to be within 100-200 μm of a blood supply to receive adequate oxygen and nutrients for survival. Otherwise, due to limitations of diffusional transport, the cells in the interior regions of the artificial scaffold can experience hypoxia or anoxia and undergo cellular degeneration and necrosis. Hence, this necessitates the formation of appropriate in vitro three-dimensional (3-D) plexuses of new blood vessels within the pre-implanted biomaterial constructs through the process of in situ de novo vasculogenesis/angiogenesis for organ tissue engineering. To this end, here we demonstrate the application of 3-D matrix scaffolds composed of type I collagen to address these concerns.