Electrospun PVP/ZnO/HA Coatings on Silane-Modified ZK60: Corrosion, Antibacterial Activity, and In Vitro Apatite Formation

Abstract

This study investigated a two-stage surface modification strategy for ZK60 magnesium alloy based on 3-aminopropyltriethoxysilane (APTES) pretreatment followed by electrospun polyvinylpyrrolidone (PVP) nanofibers containing ZnO and hydroxyapatite (HA) nanoparticles. Three PVP/ZnO/HA formulations were prepared to examine the effect of nanoparticle loading, and corresponding coatings with and without APTES pretreatment were compared. The coatings were characterized using Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM/EDX), and a cross-hatch adhesion test. Corrosion behavior was evaluated in simulated body fluid (SBF) using open-circuit potential (OCP) monitoring and potentiodynamic polarization. Antibacterial activity was screened against S. aureus and E. coli, while in vitro apatite-forming ability was evaluated after 14 days of SBF immersion. XRD analysis confirmed the presence of crystalline HA and ZnO phases in the electrospun coating. The APTES-pretreated specimen showed a lower coating-removal area (3.52%) than the electrospun-only specimen (8.05%). The best-performing APTES-pretreated specimen exhibited a corrosion rate of 3.003× 10-3 mm· year–1 compared with 0.488 mm· year–1 for uncoated ZK60, corresponding to a 99.38% reduction in the short-term electrochemical corrosion rate. The selected APTES-pretreated/electrospun specimen exhibited inhibition zones of 22 mm against S. aureus and 28 mm against E. coli. After SBF immersion, this specimen exhibited the highest Ca and P contents and a Ca/P atomic ratio of 1.63, indicating enhanced in vitro apatite-forming ability. Overall, the results indicate that APTES pretreatment combined with electrospun PVP/ZnO/HA nanofibers improves coating retention, suppresses the initial electrochemical corrosion activity of ZK60, and provides antibacterial and apatite-forming surface characteristics under the investigated in vitro conditions.