Researchers in biodegradable metals have been putting efforts to accelerate the corrosion of ironbased biodegradable metals. These include by alloying iron with manganese and noble elements such as silver, but further increase to the corrosion rate is still needed. In this study, a set of bimodal nano/microstructured Fe-30Mn-1Ag alloys was prepared through mechanical alloying and spark plasma sintering. The alloys were characterized and tested for their corrosion behavior in Hanks' solution at 37 o C and for their mechanical properties. The bimodal-structured alloy possessed a mixture of austenitic (γ-FeMn) and ferritic (α-Fe) phases, while the nano-and macro-structured ones were essentially composed of γ-FeMn and α-Fe phases, respectively. Addition of 1-3 wt.% of silver into the nanostructured alloy increased its corrosion rate from 0.24 mm/year to 0.33 and 0.58 mm/year for Fe-30Mn-1Ag and Fe-30Mn-3Ag, respectively. Whilst, the bimodal Fe-30Mn-1Ag alloy corroded at a higher rate of 0.88 mm/year. This alloy also possessed an interesting combination of high and low micro-hardness phases that contributed to high shear strength of 417 MPa and shear strain of 0.66. Detailed discussion on the relationship of microstructure with corrosion behavior and mechanical properties is presented in this manuscript.
The addition of noble elements such as Ag was shown as a successful method to accelerate the corrosion rate of absorbable Fe-based alloys. One major concern of Ag addition is its effect on hemocompatibility and biocompatibility. In this study, in vitro degradation and surface analysis of Fe-30Mn-xAg (x= 0, 1 and 3 wt.%) alloys as well as their effects on hemocompatibility and cell viability of human umbilical vein endothelial cells (HUVECs) were investigated. The static degradation rate of the alloys was 4.97, 4.69 and 4.49 mg/cm 2 for Fe-30Mn, Fe-30Mn-1Ag, and Fe-30Mn-3Ag, respectively. The surface analysis after degradation showed that γ-FeOOH was formed on Fe-30Mn-3Ag, while α-FeOOH was more dominant on Fe-30Mn and Fe-30Mn-1Ag. As γ-FeOOH is more soluble than α-FeOOH, it assists further degradation of Fe-30Mn-3Ag alloy. The high amount of Ag, induced hemolysis ratio however, inhibited coagulation by decreasing the platelet adhesion. Fe-30Mn-1Ag and Fe-30Mn-3Ag alloys shown improved cell viability compared to that of Fe-Mn alloy. Shear yield strength and shear elastic modulus of the samples after immersion tests were increased while the ultimate shear strength was not affected. Based on acceptable hemolysis rate, low platelet adhesion, acceptable cell viability, and appropriate mechanical properties after degradation Fe-30Mn-1Ag can be considered as a suitable blood-contacting Fe-based absorbable alloy.
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