Effects of current control modes on the morphological and biological properties of graded FeCrNi metal-matrix coatings containing Al2O3 nanoparticles for cardiovascular applications

Abstract

Implant coatings represent the most effective strategy to address multiple issues, ultimately increasing implant longevity and improving implant compatibility. In this study, we investigated the electrodeposition of a novel graded FeCrNi/Al₂O₃ coating on a 316L substrate for cardiovascular implants using direct current (DC) and pulsed current (PC). The effects of a current density range of 3–11 A dm⁻² and decreasing the duty cycle from 90 % to 50 % and subsequently to 10 % on the concentration of Al₂O₃ nanoparticles in the FeCrNi matrix, as well as on the microstructure and morphological properties, were studied using scanning electron microscopy (SEM). Additionally, structural characterization of the FeCrNi/Al₂O₃ films was performed using X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). To assess the cytocompatibility of the samples, human coronary artery endothelial cells (HCAEC) were used. The results indicate that the PC provides a uniform microstructure and a smoother surface compared to the direct current DC. The study also reveals that the PC results in fewer defects and microcracks in the coating due to reduced formation of chromium hydrides in the layer and a significant reduction in stress during the deposition process. When using PC, an increase in particle incorporation in the coating was achieved, but no effect of changing the duty cycle was found. The highest deposition rate of Al₂O₃ was achieved at a current density of 11 A dm⁻² with an electrolyte containing 10 g L⁻¹ Al₂O₃. The FeCrNi/Al₂O₃ coatings exhibit low cytotoxicity when deposited using a high alumina content and DC, showing cell viability of over 90 %. However, only a few samples demonstrated cell viability higher than 80 % on day three. The proposed composite coating may represent an initial step towards improving implant coatings for cardiovascular stent materials.