Vascularization in Tissue Engineering: Angiogenesis versus Inosculation

<i>Background/Purpose:</i> The key challenge in tissue engineering is the establishment of an efficient vascularization for tissue constructs guaranteeing long-term survival and function. Vascularization may be achieved by the stimulation of angiogenesis or the inosculation of preformed microvascular networks within the implants to the host microvasculature. The present review provides an overview of these two concepts applied in tissue engineering. <i>Methods:</i> A literature search was performed in PubMed for publications focusing on vascularization, angiogenesis and inosculation in tissue engineering. <i>Results:</i> Several strategies have been proposed to stimulate the ingrowth of new blood vessels into tissue constructs. These include the modification of the chemical composition and architecture of scaffolds, their bioactivation by incorporation of growth factor delivery systems or by cell seeding as well as the stimulation of stem cell recruitment. However, because angiogenesis is a time-consuming process, all of these approaches cannot prevent ischemic cell death within larger 3-dimensional tissue constructs during the initial phase after implantation. To overcome this problem, in vitro or in situ prevascularization has emerged as a novel concept in tissue engineering. This bears the advantage that preformed microvascular networks within tissue constructs simply have to inosculate with the host microvasculature at the implantation site to get completely blood-perfused within a short period of time. <i>Conclusions:</i> During the last years, considerable progress has been made in the development of promising vascularization strategies in tissue engineering. Particularly the inosculation of preformed microvascular networks has the great potential to markedly improve the survival of tissue constructs after implantation. The optimization of this vascularization strategy may pave the way for a broad clinical use of tissue engineering applications in the future.