Apatite formation and cellular response of a novel bioactive titanium.

The modification of titanium and titanium alloy surface properties by chemical and electrochemical techniques has opened new possibilities to improve the bioactivity and, in general, the biological performance of the implants once in vivo. One of the main aims is the achievement of a surface oxide layer that stimulates hydroxylapatite mineralization and, also, shows osteoconductive properties once in the host. In the present study, two different bioactive surfaces have been prepared following the method purposed by the group of Kokubo and a new method, BioSpark, involving high voltage anodic polarisation and alkali etching both on surface mineralization potential. The aim of the present work was to evaluate and compare the mineralization capability and the early cell response of titanium modified with a new bioactive method and with a well-known and widely tested biomimetic treatment, both compared to non treated titanium. Physical and chemical (energy dispersion spectroscopy, thin film X-ray diffractometry) and morphological (scanning electron microscopy) characterisation of the novel surface features has been performed. Also the effect of the novel surface properties on both hydroxyapatite precipitation and early cellular response has been investigated using in vitro models. The results have shown that both treatments produce an active outer layer on titanium but do not impair cells activity and support osteoblasts processes. BioSpark showed high bioactivity and good mineral phase deposition even after early incubation time, these properties were found in Kokubo's surface as previously published. Mineralisation mechanisms of the two materials were different, and while this mechanisms was well characterised and reported for Kokubo's surface, it was still unclear for BioSpark. In this paper an explanation was given and catalytic properties of the latter surface was bound to both well known crystal titanium oxide exhibiting anatase lattice and a certain level of calcium and phosphorus doping, which promoted chemical and physical variation in anatase properties. At the same time early osteoblasts response to Kokubo's and BioSpark's surface was characterised and, no significant differences was found.