In vitroandin vivocorrosion properties of new iron–manganese alloys designed for cardiovascular applications

Abstract

The principle of biodegradation for the production of temporary implant materials (e.g. stents) plays an important role in the treatment of congenital heart defects. In the last decade several attempts have been made with different alloy materials—mainly based on iron and magnesium. None of the currently available materials in this field have demonstrated satisfying results and have therefore not found entry into broad clinical practice. While magnesium or magnesium alloy systems corrode too fast, the corrosion rate of pure iron‐stents is too slow for cardiovascular applications. In the last years FeMn alloy systems were developed with the idea that galvanic effects, caused by different electrochemical properties of Fe and Mn, would increase the corrosion rate. In vitro tests with alloys containing up to 30% Mn showed promising results in terms of biocompatibility. This study deals with the development of new FeMn alloy systems with lower Mn concentrations (FeMn 0.5 wt %, FeMn 2.7 wt %, FeMn 6.9 wt %) to avoid Mn toxicity. Our results show, that these alloys exhibit good mechanical features as well as suitable in vitro biocompatibility and corrosion properties. In contrast, the evaluation of these alloys in a mouse model led to unexpected results—even after 9 months no significant corrosion was detectable. Preliminary SEM investigations showed that passivation layers (FeMn phosphates) might be the reason for corrosion resistance. If this can be proved in further experiments, strategies to prevent or dissolve those layers need to be developed to expedite the in vivo corrosion of FeMn alloys. © 2014 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 103B: 649–660, 2015.

Comparison of the electrochemical behavior of CoCrWNi, CoCrFeNiMo, and CoNiCrMo alloys

“…Other work involving Fe in Hanks solution showed that Fe phosphate was present in a layer of corrosion product precipitated on a surface oxide (thought to be Fe 3 O 4 ) (Kocijan, Milosev, & Pihlar, 2003). Furthermore, an FeMn phosphate passivation layer was found to be formed on FeMn alloys (0.5, 2.7, and 6.9 wt% Mn) in mice and was thought could explain the lack of significant corrosion observed after 9 months (Drynda, Hassel, Bach, & Peuster, 2015). Both CoCrFeNiMo and CoCrWNi contained 2% Mn as well as Fe, whereas CoNiCrMo had less than 0.01% Mn and only 0.14% Fe (Pound, 2010).…”

Sustained release from biodegradable metallic matrix—The entrapment of drugs within iron

“…Oxidation of the disc is much slower because of its compactness, and therefore this decrease is not seen for this format. It could also be that the residual iron phosphate (indicated in the XRD) helps in preventing the penetration of oxygen [30]. The release profiles from the discs also show that there is a population of drug molecules that is so tightly entrapped, that it remains unreleased, compared to powder in PBS: 35% of chd and 20% of rap are released from the discs.…”

Are Fe-Based Stenting Materials Biocompatible? A Critical Review of In Vitro and In Vivo Studies

“…In 2014, Fe-based alloys found implementations also in osteosynthesis and cylindrical pins were implanted into the rat femur until 52 weeks, showing that the tissue surrounding Fe implantation contains a significant amount of Fe ions but without toxicity [69]. Subcutaneous implantations in mice models did not allow the material to corrode, so any prediction about the suitability of Fe-based materials was not possible [58]. Finally, more recently, a large study was conducted by Lin et al, which involved nitrited Fe scaffold implantation in several abdominal aortas of rabbits and minipigs.…”