Magnesium in the murine artery: Probing the products of corrosion

Many publications are available on the physiological and pseudophysiological corrosion of magnesium and its alloys for bioabsorbable implant application, yet few focus on the characterization of explanted materials. In this work, commercially pure magnesium wires were corroded in the arteries of rats for up to 1 month, removed, and both bulk and surface products characterized. Surface characterization using infrared spectroscopy revealed a duplex structure comprising heavily magnesium-substituted hydroxyapatite that later transformed into an A-type (carbonate-substituted) hydroxyapatite. To explain this transformation, an ion-exchange mechanism is suggested. Elemental mapping of the bulk products of biocorrosion revealed the elemental distribution of Ca, P, Mg and O in the outer and Mg, O and P in the inner layers. Carbon was not observed in any significant quantity from the inner corrosion layer, suggesting that carbonates are not a prevalent product of corrosion. Backscatter electron imaging of cross-sections showed that thinning or absence of the hydroxyapatite in the later stages of degradation is related to local thickening of the inner corrosion layer. Based on these experimental observations, mechanisms describing corrosion in the quasi-steady state and during terminal breakdown of the magnesium specimens are proposed.