Bioactive HA/PVDF-HFP nanocomposite coatings for superior corrosion protection of 316 L stainless steel

Reliable osseointegration of metallic implants remains a significant challenge in orthopaedic and dental applications. Advanced surface coatings are required to improve bone bonding and ensure long-term stability. While hydroxyapatite (HA) coatings are widely used, many studies rely on synthetic HA. This study proposes a novel nanocomposite coating that uses HA derived from waste bovine bone via mechanosynthesis as a bioactive component. This HA is combined with poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP), which is a highly chemically resistant, thermally stable, hydrophobic polymer, to address the issue of HA porosity. The corrosion resistance of the coatings was evaluated in a simulated body fluid (SBF) over 28 days using potentiodynamic polarisation and electrochemical impedance spectroscopy. Scanning electron microscopy, energy-dispersive X-ray spectroscopy and X-ray diffraction were employed to confirm apatite formation, elemental composition and crystalline phase development. Of the systems tested, a bilayer coating consisting of a PVDF-HFP base layer and a top layer containing 20 wt% HA/PVDF-HFP performed best, exhibiting a corrosion rate of 0.0007 mm/year. Impedance results revealed a stable semicircle after 21 days, indicating coating integrity and apatite formation, which is essential for bone integration. XRD confirmed progressive hydroxyapatite diffraction peak development at 26 ° and 32 ° after 14 and 28 days of immersion. This coating provides enhanced corrosion protection and controlled bioactivity, making it a promising material for biomedical applications.