Biodegradable implant materials are rising alternative materials as the diseased or injured tissue can heal and remodel over time and the implant material is no longer necessary. We present our study on the influence of 3.5 wt% Cu addition (FeMnCCu) on the biodegradable Fe-30Mn-1C alloy (FeMnC). Thereby, the influence of Cu on the microstructure and initial degradation behaviour by means of potentiodynamic polarisation is presented. After immersion in a bacterial growth medium, the degradation layer was further investigated by glow discharge optical emission spectrometry and transmission electron microscopy with energy-dispersive X-ray analysis and concerning the ion release with inductively coupled plasma optical emission spectroscopy (ICP-OES). To the best of our knowledge, antibacterial behaviour was compared to clinically applied 316L stainless steel for the first time. The three bacterial strains Pseudomonas aeruginosa, Staphylococcus aureus and Escherichia coli were utilized as these are the main strains causing implant-related infections.
Both Fe-based alloys exhibited a single-phase austenitic microstructure. For the Cu-modified alloy a significant influence on the degradation was found in static immersion tests. Additionally, a significant higher Fe and Mn ion release could be detected due to the Cu alloying. Furthermore, the degradation layer was more heterogeneous and thicker for FeMnCCu.
In this preliminary study, an inherent antibacterial effect of FeMnC on S. aureus, P. aeruginosa and E. coli was detected. This effect is probably caused by the formation of reactive oxygen species during degradation. Furthermore, the addition of Cu enhanced the antibacterial effect on P. aeruginosa. As this strain is quite prominent in causing coronary stent infections, FeMnCCu is a promising alloy for temporary stent implants. On E. coli, FeMnCCu had a quite different effect on the cell number as well as on the ion release. An increased proliferation of the bacterial cells was accompanied by an increased ion release compared to the ion release of the alloy without bacterial influence. In follow-up studies, the mechanisms of the Cu ions have to be further investigated in more detail.