Magnesium alloys are great candidates for deployment in biodegradable implant applications. They often comprise significant amounts of alloying elements to improve their mechanical properties. One well-known example is WE43, which contains about 4 wt.% Y and 3 wt.% rare-earth (RE). In contrast, we have developed in recent years fine-grained, lean Mg-based alloys with alloying contents below 1 at.%, such as ZX10 (MgZn1.0Ca0.3, in wt.%) [1] and MgCa [2]. Via hot-extrusion processing we can tune the microstructure and thus the properties of these lean Mg alloys [2]. Varying the extrusion parameters, we can produce high-strength alloys with a yield strength >400 MPa at ductility >5% or highly ductile alloys with ductility >30% at intermediate strength.

Highly ductile plates and high-strength screws of lean, ultrahigh-purified MgCa (X0) were implanted in the pelvis of six adult female Swiss alpine sheep and compared with WE43 [3]. Some of the X0 implants were subjected to PEO coating. Fluorescent dyes were injected at two time points before the animals were sacrificed after 8 weeks. MicroCT and histological studies were performed at these time points together with mass-loss investigations. The average degradation rate of X0 (coated or uncoated) was 0.31 mm/year and slightly less than that of WE43 (0.37 mm/year). The bone-implant contact was found to be significantly higher for X0 than for WE43. Importantly, the RE-containing degradation products of WE43 stayed in its original place, whereas X0 only revealed a very thin degradation-product layer. This together with X0’s lower degradation rate explains the much better osseointegration of X0 compared to WE43.

[1] J. Hofstetter, et al. JOM, 2014, 66, 566-572.
[2] T. Akhmetshina et al., 14th Biometal Conference (Aug. 24-29, 2022), Europ. Cells and Materials, 2023, in press.
[3] L. Berger et al., 14th Biometal Conference (Aug. 24-29, 2022), Europ. Cells and Materials, 2023, in press.