EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

Metallic biodegradable alloys constitute a new class of biomaterials for temporary applications. Fe-Mn-C steels are particularly attractive for the production of very thin implants, including stents, mainly due to their outstanding mechanical properties. To cut the complex geometry of stents, laser processing is considered the gold standard, even if it results in debris and slag materials on the surface that need to be removed. Electro polishing constitute the envisaged technique for removing debris and slag, and achieving the appropriate surface finishing of the device made of corrosion-resistant metals. However, for degradable metals, electro polishing may initiate the degradation process, and mechanical polishing is often privileged, although its homogeneity is not comparable with electro polishing. This work aimed to investigate the influence of different electrolytes for electro polishing, and compare with mechanical polishing.
Samples were mechanically polished with 80-240 grit Si-C papers prior to subsequent treatments: a mirror finish mechanical polished (MP) and electropolished samples (EP). Three distinct electrolytes EP1 (ethanol, perchloric acid and glycerol), EP2 (perchloric acid, acetic acid and glycerol) and EP3 (choline chloride and ethylene glycol) were selected. Morphology, chemical composition, topography and wettability were assessed by scanning electron microscope (SEM), X-Ray Photoelectron spectroscopy (XPS), Atomic Force Microscope (AFM), and by water contact angle (CA). Electrochemical tests as potentiodynamic polarization (PDP) and impedance spectroscopy (EIS) measurements were carried out for treated samples in modified Hanks’ solution (MH) and M199 medium.
EP samples showed the typical morphology and wavily structure, mainly due to the dissolution mechanisms governed by electrolyte composition, temperature and duration. Briefly, EP2 samples presented a smoother surface if compared to mechanical polished ones or to other conditions attaining the same cell viability behaviour. Results demonstrate that electro polishing under controlled conditions constitute the choice for surface finishing of Fe-based biodegradable metals.