Angiogenesis and Vascularity for Tissue Engineering Applications

Abstract

Tissue engineering is a field of medicine that has experienced significant growth in prominence over the past three decades. Though traditional interventions exist for many medical maladies, tissue engineering aims to combat such disorders through the synthesis of body tissues and organs, resulting in functional implants. Tissue engineering takes an innovative approach, often utilizing autologous stem cells for tissue construction or materials that are biocompatible while avoiding immune rejection (Nomi et al., 2002). Despite its immense successes, a major hurdle still faces tissue engineering. Large volumes of implanted tissue are unable to stimulate the formation of necessary blood vessels required for their survival. In the body, naturally occurring, equivalent vascular networks serve vital functions in gas and nutrient exchange, metabolic processes, and waste expulsion. Though individual, large vessels have been successfully engineered for implant, it is still exceptionally difficult to fashion a stable and sustainable network of vessels for large volumes of tissue (Nomi et al., 2002). Neovascularization after tissue damage requires a level of positive and negative control that has not been successfully replicated in a laboratory environment to date. As such, rapid de novo synthesis of a controlled, established vascular network remains a challenge today. Angiogenesis is the morphogenic process of forming new blood vessels from pre-existing ones (Laschke et al., 2006; Dai and Rabie, 2007; Li and Rabie, 2007). This event plays an important, normal physiological role in wound healing, tissue repair, pregnancy, and exercise (Ferrara and Davis-Smyth, 1997), and exists in contrast to vasculogenesis (the formation of the every first blood vessels in the body, and especially predominant in embryological development). Yet, the abuse of angiogenesis, leading to an uncontrolled vascular formation as a consequence of epigenetic influence, nucleotide polymorphisms, or endocrine irregularities can also result in tumor formation (Verbridge et al., 2010). However, angiogenesis is clearly an activity that is central to development and tissue maintenance. Successful modulation of angiogenesis can have profound therapeutic outcomes for organs and tissues deprived of an adequate, stable vasculature. Studies from the last two decades have shown that the manipulation of various factors directly influences angiogenic outcome.