Electropolishing Fe-based biodegradable metals for vascular applications: impact on surface properties, corrosion and cell viability

Abstract

Biodegradable metals constitute a new class of materials for medical application. By breaking the paradigm that a metallic biomaterial to be implanted in the body must be corrosion resistant, biodegradable metals advance surgery allowing clinicians to dispose of temporary devices. Among them, Fe–Mn–C steel has emerged due to its outstanding mechanical properties, while its degradation rate must be carefully controlled. For this purpose, especially for medical devices, the surface finishing plays a pivotal role and influences both the corrosion behavior and biological response of these materials. Therefore, this research investigated the impact of electropolishing (EP) processes on the Fe–Mn–C alloy surface finishing in terms of composition, morphology, topography, and wettability. Three electrolytes were carefully selected and used in this study: EP1 (ethanol, perchloric acid, and glycerol), EP2 (perchloric acid, acetic acid, and glycerol), and an ionic liquid EP3 (choline chloride and ethylene glycol). Corrosion behavior and cell viability were investigated and compared with those obtained on mechanically polished (MP) samples. The results displayed that electropolishing was governed by two mechanisms: 1) controlled mass transport for EP1 and EP2, and 2) an adsorption mechanism for EP3. Among the tested conditions, EP2 emerged as a promising overall EP process. It promoted the smoothest and most hydrophilic passivated surface (R_a ∼ 10 nm, WCA = 53°, respectively) and the highest ratio of metal oxides to metallic elements. In addition, EP2 exhibited appropriate corrosion behavior suitable for biodegradable metal devices by inducing the formation of a protective oxide layer. Furthermore, cell viability with EP2 was comparable to that observed with MP. These findings emphasize the potential of electropolishing for enhancing the properties of Fe–Mn–C alloys, paving their applicability, especially in cardiovascular devices.