Surface properties of biomimetic nanocrystalline apatites; applications in biomaterials

The term biomimetic is used with different meanings; applied to materials it is often intended to denote preparative techniques and/or properties mimicking those of biological materials. Biological nanocrystals are characterized by the existence of non-apatitic domains, which have sometimes been interpreted as a sign of formation of precursor phases. Finally, spectroscopic (FTIR and SS-NMR) analyses of wet samples revealed that the surface hydrated layers were structured, and that the structuralization was related to surface composition and easily altered by fast, reversible ionic exchange, leaving the apatite domains unchanged. The hydrated layer shall not be considered as a Stern double layer but a result of the precipitation process of biomimetic apatites. This layer is believed to decrease the water-crystal interfacial energy and to favor the formation of the nanocrystals in aqueous media. From a thermodynamic point of view, however, the apatite domains are the most stable and with time they develop at the expense of the hydrated layer, incorporating some of the mineral ions presenting this layer.