Mechanically driving supersaturated Fe–Mg solid solution for bone implant: Preparation, solubility and degradation

Abstract

Fe has attracted great attention as biodegradable bone implant. Unfortunately, its degradation rate is too slow for bone repair. It is well known that the lower the electrode potential is, the faster the metals degrade. In the case of dissolving low electrode potential species (Mg for instance) into Fe lattice, the corrosion potential of the matrix can be negatively shifted and the overall degradation rate can be accelerated. However, Fe and Mg are immiscible in equilibrium due to their large differences in melting and boiling temperature. In this study, a supersaturated Fe–Mg solid solution was developed in solid-state by mechanical alloying (MA). In detail, Fe particles experienced cycled mechanical impact and friction during MA, which produced a large number of dislocations and defects. In this condition, Mg atoms were forcibly diffused into Fe lattice along with the motion of dislocations and defects. The results showed that about 8.5 at.% Mg was dissolved in Fe (0.02 at.% in equilibrium). Subsequently, the MA powders were fabricated into bone implants by selective laser melting (SLM), in which the fast laser scanning speed resulted in a rapid cooling rate. The molten liquid passed the immiscible zone quickly, thereby avoiding the separation of Mg solute. SLMed implants exhibited a lowered electrode potential (−0.93 V) comparing with Fe. Additionally, the implants also had good cytocompatibility and promoted cell proliferation.