*3.1. Angiogenesis*

The formation of capillaries from pre-existing vessels to expand the microvascular system by increasing the capillary density is called angiogenesis. Driven by several growth factors such as hypoxia-inducible factor 1<sup>α</sup>, vascular endothelial growth factor (VEGF) [40] and inflammatory mediators as well as inflammatory cells (mainly monocytes [41]), a local milieu is formed [42] which promotes the proliferation and migration of endothelial cells, pericytes and smooth muscle cells. Thereby, "the amplification of the vascular network occurs within a short time due to either abluminal outgrowth (sprouting) or intraluminal division (intussusceptive growth) of capillaries" [43]. In contrast to arteriogenesis, angiogenesis is mostly driven by metabolic demands (i.e., hypoxemia) [44]
