Surface modification of orthopedic implants by optimized fluorine-substituted hydroxyapatite coating: Enhancing corrosion behavior and cell function

Abstract Fluorine may only have negative effects on bone metabolism if the optimum concentration of fluorine would not be determined, especially in osteoporosis. In this study a nano-porous and uniform fluorhydroxyapatite (FA) coating in different concentration of fluorine could be deposited on the 316 L substrate with a thickness of 50 μm. Fluorine can have influence on cell proliferation, matrix production, ALP releasing, coating dissolution rate, bio activity, and corrosion resistivity. The dissolution rate of the coating evaluated by ICP and found with an increase in fluorine due to the elimination of CaO, Ca2+ releasing decreased. The results of SBF and MTT exhibited the fluorine within the apatite structure enhanced the growth of natural apatite and function of human osteoblast like cell (MG-63). Furthermore, cell density and attachment showed an enhancement while fluorine increased. Surprisingly the ALP activity test showed the mineralization ability of coating would be improved significantly in presence of fluorine. Furthermore potentiodynamic polarization showed with increasing fluorine, the current density decreased from 112 to 13 nA/cm2. Corrosion property of FA is higher because it is too stable but can also persuade to severe adverse effects like osteomalacia. According to the achieved results, 75% partially-substituted fluorine within apatite structure was introduced as a proper combination of biocompatibility while 100% substituted fluorine could be a better candidate in corrosion resistant performance.