In vitro evaluation of the surface effects on magnesium-yttrium alloy degradation and mesenchymal stem cell adhesion

Magnesium (Mg) alloys present many advantages over current materials used in medical implants and devices. However, the rapid degradation of Mg alloys can raise the local pH and create gas cavities. Fundamental understanding of their biodegradation processes is necessary for their success in clinical applications. This study investigated how the oxidized and polished surfaces of a Mg-yttrium (Y) alloy affected the degradation mode and rate in cell culture media versus deionized water. The interactions of the alloy surfaces with cells were examined in vitro using bone marrow derived mesenchymal stem cells, since they are critical cells for bone tissue regeneration. The polished surface was more stable than the oxidized surface in cell culture media, but less stable in water. When comparing polished and oxidized surfaces, their degradation modes were similar in water, but different in cell culture media. The microstructure, roughness, and oxygen content of the alloy surface contributed to these differences. The presence or absence of a stable degradation layer determined the rate of Y loss and the inhibiting or promoting behavior of Y on degradation. The initial alloy surfaces not only influenced the degradation, but also determined cell attachment, which is critical for tissue integration. The polished surface showed more cell adhesion than the oxidized surface, mainly because of its slower degradation rate and lesser effect on the local pH. In conclusion, this study demonstrated that both the Mg alloy surfaces and the immersion fluids played important roles in controlling the degradation and cellular interactions.