At present time titanium and its alloys are widely used as biomedical materials, especially in those applications where good mechanical properties and high biocompatibility are required. Unlike bioactive materials, that bond quickly to living bone through a bone like apatite layer titanium does not have the bone-bonding ability and is usually encapsulated by fibrous tissue layer after implantation. It was previously shown that titanium induces bone-like apatite formation in simulated body fluid (SBF) when it has been treated with NaOH solution to form amorphous sodium titanate layer on its surface.
In this study we showed that the sodium titanate layer formation and subsequent apatite precipitation is affected by titanium processing prior to the alkali treatment. Sand blasted, abraded and machined titanium samples were treated with NaOH solution and soaked in SBF. The precipitation of apatite was evaluated using thin film x-ray diffraction (TF-XRD). While the precipitation rates on the sand blasted and abraded surfaces were comparable the apatite formation on machined samples exhibited low reproducibility and the incidence of apatite spherulites was scarce.
During the alkali treatment the protective oxide layer dissolves and dissolution of titanium in an active state occurs. In our study the time dependence of the corrosion potencial of titanium during the treatment in NaOH was measured. We found that a heat treatment of titanium at 300ยฐC for 15 minutes can prevent the oxide layer from dissolving and thus inhibit the sodium titanate layer formation. It is known that even higher temperatures can be reached locally during the machining especially when sufficient cooling is not ensured.
The surface profiles of sand blasted, abraded and machined samples were also measured and parameters characterizing the surface roughness were evaluated. The average roughness parameter R a and the mean spacing of adjacent local peaks S showed that abrasion and sandblasting produce micro rough surfaces whereas machined surface having higher values of both R a and S consists of larger peaks and valleys. This difference can significantly affect the reactivity of the surface and subsequently the sodium titanate layer formation and the apatite precipitation.