Plasma processing for inducing bioactivity in stainless steel orthopaedic screws

The work presented in this paper is centred on applying plasma processing for inducing bioactivity (ability of a material to bond with bone) in otherwise bioinert stainless steel screws commonly used in orthopaedic surgery. As-received cortical stainless steel screws were hydroxylated using a patented two-step plasma process developed by the authors. The bioactivity of the screws thus processed was investigated in vitro by treating them with simulated body fluid (SBF). The SBF treatment resulted in a thin, continuous surface layer of hydroxyapatite (HA, calcium hydroxy phosphate) on the screws, thus confirming their bioactivity. The plasma processed screws were also compared with wet chemically processed screws for the growth of HA from SBF, and it was found that the HA layer on the plasma processed screws exhibited higher (complete) substrate coverage. The realisation of bioactive screws, in particular fine-threaded stainless steel screws, offers a major advancement towards the fixation of both internal and external orthopaedic implants.