In vitro models of angiogenesis.

Neovascularization can be categorized into two general processes: vasculogenesis and angiogenesis. Angiogenesis is the formation of new capillaries from pre-existing vessels, requiring growth factor driven recruitment, migration, proliferation, and differentiation of endothelial cells (ECs). Complex cell-cell and cell-extracellular matrix (ECM) interactions contribute to this process, leading finally to a network of tube-like formations of endothelial cells supported by surrounding mural cells. The study of angiogenesis has broad clinical implications in the fields of peripheral and coronary vascular disease, oncology, hematology, wound healing, dermatology, and ophthalmology, among others. As such, novel, clinically relevant models of angiogenesis in vitro are crucial to the understanding of angiogenic processes. We highlight some of the advances made in the development of these models, and discuss the importance of incorporating the three-dimensional cell-matrix and EC-mural cell interactions into these in vitro assays of angiogenesis. This review also discusses our own 3-D angiogenesis assay and some of the in vitro results from our lab as they relate to therapeutic neovascularization and tissue engineering of vascular grafts.