The effects of heat treatments and bead size on the corrosion of porous F75 in saline and serum.

An accelerated anodic corrosion method was used to study the effects of heat treatment and bead size on corrosion and metal ion release of porous coated F75 cylinders in saline and serum. Three heat treatments were used: a standard process for F75 implants (HTA), the standard plus an additional hour in air to produce a thin oxide film (HTA'), and a sintering in high vacuum to produce a chromium-depleted surface (HTB). Three bead sizes of similar composition were used, with approximate sizes of 215, 300, and 560 microns. The results demonstrated that HTA' had the lowest corrosion rate and that of HTB was significantly greater than either HTA or HTA'. The corrosion rates of HTA and HTA' were significantly greater in serum as compared with saline, whereas that of HTB was not affected by the presence of serum, suggesting an interaction between chromium and serum proteins. Bead size had a minimal effect on the corrosion rate of HTA'. For HTA, the small beads had the highest corrosion rate; the lowest was with the medium-sized beads. Bead size had the most significant effect with HTB, with that of the smaller beads having the higher corrosion rates. The effects of bead size were less consistent in serum, suggesting that protein adsorption may mask some of the surface area effects. It is concluded that the oxide film does reduce corrosion, that proteins do have an influence on the corrosion of F75, and that this method can be a useful tool for studying the effects of improved heat treatment methods on the corrosion rate of F75 implants.