BEHAVIOR OF HYDROXYAPATITE COATED TITANIUM AS A FUNCTION OF NaOH PRETREATMENT

Resumen

Titanium plates have been submitted to a chemical pretreatment with NaOH solutions at 130ºC followed by heat-treatment at 600ºC. These pretreated titanium samples were then soaked in a Simulated Body Fluid (SBF) during four weeks in order to promote the nucleation and growth of hydroxyapatite (HA) on the surface of the titanium under biomimetic conditions. The free electrochemical potentials of the titanium samples were measured during four weeks while undergoing the biomimetic coating process. The evolution of potentials into noble directions indicates the protective characteristics of this coating. Anodic polarization curves were carried out in a usual SBF as well as a modified one, which simulates the infection condition. The best electrochemical behavior is achieved by the crack-free coating of titanium. The effects of low pH, in similar infected condition, are the reduction of free potential and increase of anodic current density. When the heterogeneous precipitation occurs by biomimetic process, cracking on the coating frequently takes place for 5 and 10M NaOH conditions. Consequently, the pretreatment of titanium at 130ºC for 1hr with 1M NaOH produces a coating with better properties than 5 or 10M NaOH. The physical nature of coating was characterized by X-ray diffraction, infra-red spectroscopy and scanning electron microscopy.