Stress-Induced Dual-Phase Structure to Accelerate Degradation of the Fe Implant

Abstract

Fe is considered as a potential candidate for implant materials, but its application is impeded by the low degradation rate. Herein, a dual-phase Fe30Mn6Si alloy was prepared by mechanical alloying (MA). During MA, the motion of dislocations driven by the impact stress promoted the solid solution of Mn in Fe, which transformed α-ferrite into γ-austenite since Mn was an austenite-stabilizing element. Meanwhile, the incorporation of Si decreased the stacking fault energy inside austenite grains, which tangled dislocations into stacking faults and acted as nucleation sites for ε-martensite. Resultantly, Fe30Mn6Si powder had a dualphase structure composed of 53% γ-austenite and 47% εmartensite. Afterward, the powders were prepared into implants by selective laser melting. The Fe30Mn6Si alloy had a more negative corrosion potential of −0.76 ± 0.09 V and a higher corrosion current of 30.61 ± 0.41 μA/cm 2 than Fe and Fe30Mn. Besides, the long-term weight loss tests also proved that Fe30Mn6Si had the optimal degradation rate (0.25 ± 0.02 mm/year).

Iron–Gold Composites for Biodegradable Implants: In Vitro Investigation on Biodegradation and Biomineralization

“…Thus, in pure Fe, the iron hydroxide is formed at cathodic sites as a result of the alkalization (5), and it can reduce the degradation rate. As stated in eq 6, the ferrous hydroxide interacts with dissolved oxygen to produce ferric hydroxide (6).…”

“…Such implants must ensure that the mechanical integrity is preserved with no stress shielding effect on the tissue. − Therefore, these implants are to be made of biodegradable metallic alloys composed of nontoxic elements that can be absorbed/metabolized by the human body. Magnesium (Mg), iron (Fe), and zinc (Zn) are considered promising candidates for developing such implants due to their biocompatible and biodegradable characteristics. − Mg-based systems have a major drawback due to their high degradation rate associated with H 2 gas evolution in the physiological environment. − Unlike Mg-based biodegradable metals (BMs), Zn-based BMs do not create any harmful effects such as H 2 gas evolution during the degradation and have a moderate degradation rate in a physiological environment. However, the poor mechanical characteristics of most Zn-based BMs limit their applicability. , …”