Surface activation and characterization of Ti6Al4V alloy foams in biomedical applications

Biomaterials, which used in load bearing applications in body, suffered from stress shielding and insufficent biocompatibility problems. The aim of this study, production of Ti6Al4V alloy foams mechanically compatible to body bones were manufactured and to get bioactiactive surfaces by surface treatment using hydrothermal treatments that allow apatite formation. Alloy foams with 100% open cells and porosities in the range 53-66% were manufactured by evaporation of magnesium from powder mixtures. Foams had elastic moduli in the range 7.6-1.0 GPa, respestively, comparable to that of body bone. Mainly bioactive sodium titanate hydrogel (Na2Ti3O7.nH2O) layer formation was observed on the foam surfaces as a result of alkali treatment in 5M NaOH aqeous solution at 60oC for 24 hours. The density of hydrogel layer increased and it transformed to crystalline sodium titanate layers as a result of post alkali heat treatment at 600oC. Although post heat treatment increased the mechanical stability of titanat layers, it degraded mechanical properties of foams. However, heat treatment under argon resulted relatively lower decrease in yield strength and ductility compared to air heat treatment and less sodium loss was detected upon argon treatment. As a result of in-vitro tests conducted by simulated body fluid (SBF), alkali treated surfaces revealed highest bioactivities among the tested samples and the surfaces allowed hydroxyapatite within 5 days. The order of bioactivities of surfaces after 25 days testing was determined as alkali treated, alkali+argon heat treated and alkali+air heat treated. On the other hand, hydroxyapatite formation on untreated surfaces was not considerable.