The effect of alloying elements on the properties of pressed and non-pressed biodegradable Fe–Mn–Ag powder metallurgy alloys

Abstract

Current trends in the biodegradable scaffold industry call for powder metallurgy methods in which compression cannot be applied due to the nature of the scaffold template itself and the need to retain the shape of an underlying template throughout the fabrication process. Iron alloys have been shown to be good candidates for biomedical applications where load support is required. Fe–Mn alloys were researched extensively for this purpose. Current research shows that all metallurgical characterisation and corrosion test on Fe–Mn and Fe–Mn–Ag non pre-alloyed powder alloys are performed on alloys which are initially pressed into greens and subsequently sintered. In order to combine the cutting-edge field of biodegradable metallic alloys with scaffold production, metallurgical characterisation of pressed and non-pressed Fe, Fe–Mn and Fe–Mn–Ag sintered elemental powder compacts was carried out in this study. This was performed along with determination of the corrosion rate of the same alloys in in vitro mimicking solutions. These solutions were synthesised to mimic the osteo environment in which the final scaffolds are to be used.Both pressed and non-pressed alloys formed an austenite phase under the right sintering conditions. The corrosion rate of the non-pressed alloy was greater than that of its pressed counterpart. In a potentiodynamic testing scenario, addition of silver to the alloy formed a separate silver phase which galvanically increased the corrosion rate of the pressed alloy. This result wasn't replicated in the non-pressed alloys in which the corrosion rate was seen to remain similar to the non-silver-bearing alloy counterparts.

Six-Month Long In Vitro Degradation Tests of Biodegradable Twinning-Induced Plasticity Steels Alloyed with Ag for Stent Applications

“…A previous study focusing on the electrochemical behavior of Fe–Mn–C–Ag alloys already showed that such lean alloying did not produce any effect on the electrochemistry of these steels, leading even to a reduced corrosion current density . A similar trend in the mass loss was already observed in the literature for tests up to 28 days in a similar solution, while other researchers observed that the presence of Ag reduced the corrosion resistance of TWIP steels from electrochemical tests. , After 3 days, SEM analyses (Figure ) showed that some voids appeared around Ag particles, indicating that galvanic coupling could effectively take place, as the difference in electrochemical potential between Ag and TWIP steels could suggest. The galvanic coupling effect could explain why more nuclei of DPs were observed at the surface at 7 days with respect to the 0Ag alloy.…”

In Vivo Evaluation of Bioabsorbable Fe‐35Mn‐1Ag: First Reports on In Vivo Hydrogen Gas Evolution in Fe‐Based Implants

“…Figure 7 gave strong evidence that the enhanced corrosion rate in the Fe‐35Mn‐1Ag is caused by the prevalence of microgalvanic corrosion, consistent with previous studies. [ 50,51,79 ] The areas around the Ag particles were all hollowed out, which indicates an advanced stage of corrosion of the Fe matrix. Niendorf et al.…”

“…Caligari Conti et al. [ 51 ] likewise reported that a 2% addition of Ag resulted in a five‐fold increase in in vitro degradation rate in fully austenitized Fe‐30Mn. Sotoudehbagha et al.…”

Biodegradation behaviour of Fe-based alloys in Hanks’ Balanced Salt Solutions: Part II. The evolution of local pH and dissolved oxygen concentration at metal interface

“…The fundamental difference in powder-processing microstructures and microstructures prepared using melt processing, is the resultant porosity in the former. To this effect, multiple groups have confirmed the increase in degradation resulting from increased percentage porosity in the tested samples [ 23 , 36 , 37 ]. Apart from this, powder-processed metal, especially FeMn-based alloys of interest in the field, are more susceptible to the formation of manganese oxide inclusions resulting from high temperature oxidation [ 38 ].…”