Biomimetic coating on titanium: evaluation of bioactivity and corrosion

Pure titanium and its alloys have been widely applied as implant material with excellent results in a long term because of their excellent biocompatibility and resistance to corrosion. Biomaterials with porous structure optimize the interfacial resistance between the material and the bone, leading to a more efficient fixation of the implant by bone growth in the pores. Titanium implants covered with calcium phosphates have received increasing application in odontology and orthopedics, and clinical studies indicate that the healthy bone tissue responds positively to the bioceramic surfaces. Calcium phosphates, particularly hydroxyapatite in the form of coating, provide a bioactive surface to the metal, which induces the direct union between the implant and the bone tissue. Consequently, the time for osseointegration and, therefore, the total time for treatment, can be reduced. Researches have been conducted to obtain a coating, in order to enhance the adherence between bone and implant, modifying the metal surface, allowing an efficient regeneration of the bone tissue, osseointegration and accelerating its growth. In this work, the effect of coating by the biomimetic method on a titanium substrate was studied, consisting of the immersion of the substrate in a synthetic SBF (Simulated Body Fluid) solution, with composition, pH and temperature similar to blood plasma. The coating was efficient for obtaining hydroxyapatite, which was confirmed by the techniques of scanning electron microscopy (SEM), X-ray diffraction (XRD) and infrared. The bioactivity assay revealed that the samples which received the coating with 1.5 SBF presented bioactive characteristic by the formation and development of the carbonated hydroxyapatite on the surface, in a superior way to the samples without coating, thus suggesting a fast osseointegration of the bone with the implant. The polarization curves showed that the titanium without coating presented a higher resistance to corrosion compared to the titanium with coating.