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The purpose of this study is to advance understanding of surface degradation kinetics for Fe-Mn bioresorbable alloys (specifically Fe-20%Mn) and target degradable fracture fixation implants for hard tissues. This study addresses how arc melted Fe-20%Mn discs degrade in a static, osteogenic medium for up to a 3 month time span. Degradation behavior of these bulk alloys was investigated using both mass loss tests for measuring long-term corrosion rates and potentiostatic tests for following the instantaneous rate of degradation. It was discovered that cold-rolling Fe-20%Mn to 77% cold work (CW) suppressed the instantaneous corrosion rate compared with the cast structure. It was also found that an unstable iron-rich oxide layer forms on the entire surface of these bulk samples and the act of machining the bulk metal into a defined shape may affect the morphology of the oxide layer on the outer edge of the samples during degradation. The mechanisms behind the surface evolution of these potential orthopedic implants are investigated in detail.

Resorbable, porous iron-manganese-hydroxyapatite biocomposites with suitable degradation rates for orthopedic applications are prepared using salt-leaching for the first time. These transient biomaterials have the potential to replace inert, permanent implants that can suffer from long-term complications, or have to be surgically removed, leaving an unfavorable void. Fe30Mn-10HA materials are newly developed to address inadequate resorption rates of degradable materials proposed for orthopedic environments in the past. In this study, controllable porosities with 300 µm diameter pores are introduced into Fe30Mn alloys and Fe30Mn-10HA composites, which enhance tissue ingrowth. For the composites, a Ca Mn O phase generated within the Fe30Mn matrix during the sintering process greatly increases degradability. The combination of this second phase and added porosity is found to contribute to increased bone-like apatite layer formation, mouse bone marrow mesenchymal stem cell attachment, and reduction of detrimental oxide layer flaking. Remarkably, after thirty days in vitro, there is a significant increase in degradation up to 0.82 ± 0.04 mm per year for 30 wt% porous Fe30Mn-10HA biocomposites, compared to 0.02 ± 0.00 mm per year for traditional nonporous Fe30Mn, thereby increasing the viability of these materials for future clinical studies.

The effects and mechanisms of dealloying Zn-diffused Fe-Mn alloys over a wide range of processing parameters have been investigated using a four-step surface modification technique. The dealloying process was applied to construct tailorable, nanoporous Fe-Mn alloys for the development of functional, bioresorbable implants. The results showed that nanoscale features can be deliberately designed by selectively leaching out the less noble metals from the outer surface layer to create an extensive variety of porous topographies. It was found that initial microstructure, Zn diffusion time, etching rate, annealing temperature and time, and the type of etching media all play a role in customizing the resulting dealloyed morphology. The resulting nano-sized structures have the potential to enhance initial cell attachment for future bioactive, resorbable materials.