Comparative study of bio-tribology and bio-corrosion behaviour of hybrid nano zinc oxide/hydroxyapatite-PMEA composite coating on stainless steel 316 L with pure n-ZnO and ZnO hydroxyapatite coatings

• (ZnOH)n/P coating on SS316L reduces friction and wear. • PMEA binder enhances coating adhesion and tribo-film formation. • (ZnOH)n/P coating shows superior corrosion and pitting resistance. • (ZnOH)n/P coating exhibits antibacterial activity and biocompatibility. Stainless steel 316 L (SS316L) implants are prone to tribological and corrosive degradation in physiological environments, resulting in wear debris, inflammation, and toxic ion release. To address these limitations, uncoated SS316L (UCS), nano-zinc oxide ((ZnO)n), nano-zinc oxide/hydroxyapatite ((ZnOH)n), and nano-zinc oxide/hydroxyapatite reinforced with poly(2-methoxyethyl acrylate) ((ZnOH)n/P) were systematically evaluated. Bio-tribology analyses were carried out using a pin-on-disc tribometer (ASTM G99 ) using simulated body fluid (SBF, Kokubo’s protocol) with a sliding distance of 100 m, load of 1 N, velocity of 5 cm/s, and 32 min test duration. Electrochemical corrosion behaviour was investigated in SBF using electrochemical impedance spectroscopy and potentiodynamic polarisation (−250 to +250 mV at 1 mV/s). Surface chemistry was examined by X-ray photoelectron spectroscopy (XPS), while antibacterial efficacy was tested against Staphylococcus aureus using the disc diffusion method. Hemocompatibility and anti-inflammatory activity were further assessed via human red blood cell (HRBC) membrane stabilisation assays. Among all coatings, the (ZnOH)n/P hybrid coating exhibited superior performance, showing a lower friction coefficient (0.25 vs. 0.40 for UCS), reduced wear rate (2 × 10⁻⁷ vs. 4 × 10⁻⁷ kg/Nm), and minimal corrosion rate (0.0001 mm/year vs. 0.028 mm/year). The level of zone of inhibition was relatively maximum (15 mm vs. 0 mm), non-haemolytic (1 % vs. 2.28 %), and provided enhanced anti-inflammatory protection (84.4 % vs. 82.92 %). Overall, the (ZnOH)n/P hybrid coating effectively improved tribological, corrosion, and biological resistance, establishing it as a promising candidate for long-term biomedical implant applications.