The effect of hydroxyapatite on the morphology and corrosion behavior of chitosan/gelatine-reduced functionalized graphene oxide coating on 316 stainless steel

Hydroxyapatite (HA)-based nanocomposite coatings on 316L stainless steel (SS316L) implants can be modified by components such as chitosan/gelatine (CS/Gel) and reduced and functionalized graphene oxide (rfGO) to improve antibacterial properties and biocompatibility. In this research, HA and rfGO were produced. HA-CS/Gel-rfGO nanocomposites with different HA values (200, 500, 800, and 1100 mg) were applied by electrophoretic deposition (EPD) at various voltages (80, 100, and 120 V). Analyzing HA and rfGO by XRD, SEM, and FTIR proved the successful synthesis. The contribution of HA and coating voltage was investigated on the morphology, microstructure, and corrosion behavior by morphological studies, electrochemical impedance spectroscopy (EIS), and potentiodynamic polarization. The possible intermolecular interactions between coating components were evaluated and found to be effective on the coating performance. Increasing HA reduced the cracks but caused unfavorable agglomerations and uneven distribution of the constituents in the coatings. Higher voltages caused voids and porosities. The coating at 1100-mg HA was porous but crack-free. The coating thickness increased by voltage and HA, from ~ 9.3 to 14.8 µm. Electrochemical polarization and EIS analysis in SBF solution showed that corrosion behavior is affected by coating morphology and bonding configurations among HA-CS/Gel-rfGO. The lowest corrosion rate occurred in the lowest HA (200 mg), with a corrosion resistance of 143,000 Ω.cm². At constant HA, increasing the applied voltage significantly decreased the corrosion resistance from 23,046 to 15,000 Ω.cm², and an induction bend occurred at 120 V. The corrosion mechanism was carefully investigated by an equivalent circuit with two time constants and corresponding dielectric capacitors.