Biomimetic coatings on titanium: a crystal growth study of octacalcium phosphate

The biomimetic approach allows the coating of metal implants with different calcium-phosphate (Ca-P) phases. Films elaborated at physiological conditions exhibited structures closely resembling those of bone mineral. For instance, octacalcium phosphate (OCP, Ca8(HPO4)2(PO4)4 . 5H2O) crystals have been deposited on titanium through a two-step procedure. After cleaning and etching, Ti6Al4V plates were immersed for 24 h into a simulated body fluid (SBF1). A thin amorphous carbonated Ca-P layer precipitated on the metal substrate. Secondly, these thinly Ca-P coated titanium substrates were immersed for 48 h into another simulated body fluid (SBF2). The thin amorphous carbonated Ca-P layer induced the fast precipitation of a second Ca-P layer of 55 microm in thickness composed of OCP crystals. The measurements of Ca and P concentrations versus soaking time in SBF2 showed that the carbonated Ca-P layer partially dissolved before the deposition of the OCP coating. X-ray diffraction (XRD) revealed that OCP crystals grew epitaxially on the substrate. OCP is known to be one of the precursors during the bone mineralization process, thereby, this new generation of biomimetic coatings are promising for orthopedic surgery.