Schematic of possible mechanism of pre-vacularized implants for bone repair. (A) Endothelial cells (red) and mesenchymal stem cells (MSCs) (yellow) are co-immobilized within a biomaterial scaffold (grey) in vitro. (B) Cells attach to the surface of biomaterial. Endothelial progenitor cells form a microvascular network, and some MSCs which have been exposed to endothelial growth supplements differentiate into perivascular cells (green). Other MSCs exposed to osteogenic supplement differentiate toward osteoblast cells. (C) After implantation in vivo, perivascular cells act to support blood vessels, the microvascular network fuses with host vasculature, osteoblasts line the surface of biomaterials, and new bone is formed with embedded osteocytes (black).