HAP Coatings for Biomedical Applications: Biocompatibility and Surface Protection Against Corrosion of Ti, Ti6Al4V and AISI 316L SS

The implants used as cardio stents, orthopedic and dental implant may be subjected to biological corrosion. Uncoated implants can be corroded in various parts of the body due to acidic erosion and oxidation. This paper presents the findings of a coating technique for the deposition of hydroxyapatite (HAP) coatings on Ti, Ti6Al4V and AISI 316L stainless steel substrates (316L SS). HAP synthesized using the sol-gel technique have been successfully produced. The corrosion behaviors of uncoated and HAP coated substrates were investigated in Ringer's and 0.9% NaCl solutions. The HAP coatings obtained by the sol gel method are effective in preventing corrosion and increased the polarization resistance values compared to the uncoated samples. Surface structures and chemical composition of the coatings were investigated by scanning electron microscopy (SEM) and energy diffraction X-ray (EDX) methods. SEM images of HAP coated substrates show cauliflower-like structures on the surface. Furthermore, the HAP coatings formed do not completely cover the surface. EDX analysis of HAP coated substrats were determined that there were Ca, O and P as well as oxides on the surface. The obtained HAP powder was characterized by X-ray diffraction (XRD) and Fourier transform infrared (FTIR) methods. In XRD analysis, it was analysed that HAP powder consisted of CaP and HAP structures. In addition, FTIR spectrum was determined that characteristic HAP absorption bands.