Figure 12. A schematic illustration of in vivo mineralization of a collagen fibril: top layer-calcium orthophosphate clusters (green) form complexes with biopolymers (orange line), forming stable mineral droplets; second top layer-mineral droplets bind to a distinct region on the collagen fibers and enter the fibril; second bottom layer-once inside the collagen, the mineral in a liquid state diffuses through the interior of the fibril and solidifies into a disordered phase of ACP (black); bottom layer-finally, directed by the collagen, ACP is transformed into oriented crystals of biological apatite (yellow). Reprinted from reference 628 with permission.