Multifunctional nanosilver-reinforced biocomposite coatings for metallic surface protection

Abstract

Stainless steel 316L is widely used for biomedical implants because of its high mechanical strength, corrosion resistance, and durability; however, its relatively bioinert surface requires modification to improve biological interaction and osseointegration. In this study, multifunctional Ag/PMMA–NiO multilayer coatings are developed on 316L stainless steel. An electroless Ag interlayer is first deposited, followed by electrostatic spray deposition (ESD) of PMMA/NiO composite coatings containing 4, 6, and 8 wt.% NiO. The coatings are characterized by X-ray diffraction (XRD), FESEM/EDS, thickness, surface roughness, wettability, and Vickers microhardness measurements. The Ag coating exhibited an average thickness of 59.1 µm, while the multilayer thickness increased to 86.6, 88.5, and 89.6 µm for 4, 6, and 8 wt.% NiO, respectively. FESEM revealed dense, continuous, and relatively homogeneous coatings, while EDS confirmed the presence of C, O, Ag, and Ni; the Ni content increased from 3.3 to 3.5 wt.% between the 6 and 8 wt.% NiO coatings. Surface roughness decreased from 0.740 ± 0.016 µm for bare 316L to 0.320 ± 0.016 µm after Ag deposition and to 0.255 ± 0.008, 0.235 ± 0.008, and 0.245 ± 0.008 µm for 4, 6, and 8 wt.% NiO, respectively. The contact angle decreased from 98.573° for uncoated 316L to approximately 58.948° and 60.948° for the 6 and 8 wt.% NiO coatings. Microhardness increased from 351 ± 3 HV to a maximum of 506 ± 4 HV for the 6 wt.% NiO coating. Overall, the 6 wt.% NiO/94 wt.% PMMA composition provided the most favorable combination of surface smoothness, wettability, and mechanical performance.

The average thickness of the nanosilver coating is approximately 59.1 µm, whereas the average thicknesses of the multilayer composite coatings are 86.6 µm for the 4% NiO-containing coating, 88.5 µm for the 8% NiO-containing coating, and 89.6 µm for the other reported NiO composition. Morphological examination further demonstrated that the deposited layers are uniform, homogeneous, continuous, and essentially free of cracks. Moreover, the coated surfaces exhibited high wettability, suggesting improved surface characteristics that may promote favorable interactions between the implant surface and the surrounding biological environment.