On the feasibility of electroforming Fe-Co alloys for biodegradable tiny medical devices

Biodegradable metallic alloys made of magnesium, iron and zinc constitute today a recognized alternative to corrosion-resistant alloys, especially for clinical application where temporary support is required. Pure Fe presents interesting mechanical properties, but also a low degradation rate. For this reason, the addition of alloying elements could be effective to improve the corrosion rate of Fe-based alloys. In this work, electroformed Co-containing Fe-based alloys were produced, and their properties investigated. Optical microscopy and x-ray diffraction were used to assess the microstructure, while scanning electron microscopy, atomic force microscopy and contact profilometry were used for the evaluation of the surface topography. Chemical composition was assessed through energy dispersive spectrometry. Potentiodynamic polarization and electrochemical impedance spectroscopy tests assessed the corrosion behavior of the materials. Results showed a complex influence of Co on surface topography and degradation properties of the samples. The electroformed alloys showed an α-Fe microstructure, while the addition of Co led to the modification of some microstructural parameters. Fe-Co alloys also showed a decrease in wettability compared to pure Fe; this was attributed to the formation of a passive layer. For most of the samples, Co addition resulted in superior corrosion resistance. Nevertheless, for sample Fe-5.0Co, a synergy between an unstable passive layer and high nano-scale rugosity (27.6 nm) resulted in increase in the corrosion rate from 0.17 mm·y -1 (for pure Fe) to 0.29 mm·y -1 . Finally, cell viability showed a unique concentration-dependent cytotoxicity of the Fe-Co alloys for fibroblasts, and all samples presented a direct kill mechanism for E. coli .