1. Apatite: a welcoming structure

Bone is a composite tissue made up of an organic part – essentially collagen – and a mineral part. The latter is a calcium phosphate that crystallizes with the "apatite" structure. Apatite compounds have been present in our bodies since the appearance of vertebrates, and we have learned to synthesize them – in order to calcify the collagen fibers produced by osteoforming cells (osteoblasts) and thus give bone improved mechanical properties, but also to provide a reactive mineral capable of taking part in ion exchange and molecular adsorption phenomena with the surrounding biological fluids. Moreover, via the bone remodeling process, the body is also able to solubilize bone apatite if necessary (through osteoclast cell activity), while leading to natural metabolites – calcium and phosphate ions typically – which can be reused by...