(D) Angiogenic sprouting of primary human umbilical vein endothelial cell (HUVEC) spheroids embedded in a collagen-based matrix was induced by the application of EGFL7 (E7), fibronectin (Fn), or a combination of both (upper row). Co-application of an integrin α5β1 blocking antibody (anti-α5β1) reduced sprouting in all cases but control (lower row). Scale bar represents 100 µm 