CO2-rich atmosphere strongly affects the degradation of Fe-21Mn-1C for biodegradable metallic implants

• CO2-rich environment, as in human blood plasma, is a missed element in most of the studies.
• The degradation behavior of Fe-Mn-C alloy is a function of test-atmosphere.
• The CO2-rich atmosphere led to the formation of a uniform and dense degradation layer.
• An incubator with CO2-rich atmosphere was proposed for a new static immersion in-vitro test.

For decades, biomaterials used as implants saved the life or improved its quality for millions around the globe. Biodegradable metals constitute a new class of biomaterials especially designed for temporary implants. Fe-based biodegradable metals are an important sub-class, but their development is limited by their tendency to degrade faster in vitro than in vivo. Blood is known to contain a high CO2 concentration. This is susceptible to form various carbonates with different stability, thus affecting and potentially decrease the material degradation rate. Therefore, this work investigates the influence of CO2 on the static degradation of Fe-21Mn-1C alloy in modified Hanks' solution. Results clearly evidenced that the presence of CO2 led to different degradation patterns and rates. Indeed, in 5% CO2 atmosphere, the degradation layer exhibited uniform, compact and dense manganese carbonate crystals, whereas, under ambient atmosphere, amorphous iron phosphorous compounds were dominant.