Synchrotron-radiation Based Microtomography for In-vivo Corrosion Measurements of Magnesium Alloys

+*Witte, F; *Fischer, J; **Nellesen, J; **Crostack HA; ***Beckmann, F; *Windhagen, H +*Hannover Medical School, Hannover, Germany [email protected] INTRODUCTION: The in-vivo corrosion of magnesium alloys has the potential to provide a new mechanism which would allow degradable metal implants to be applied in musculoskeletal surgery [1]. This would particularly be true if magnesium alloys with predictable in-vivo corrosion rates could be developed. Since the magnesium corrosion process depends on the corrosive environment, the corrosion rates of magnesium alloys under standard in-vitro environmental conditions are not directly comparable to results of corrosion rates obtained from an animal model. However, synchrotron-radiation based microtomography (SRμCT) is an accurate non-destructive method to evaluate materials and bone in the micrometer range [2]. Since there is no established non-destructive method for measuring in-vivo corrosion, we asked the research question whether or not SRμCT can be used for in-vivo corrosion measurements of magnesium alloys. METHODS: Two gravity cast magnesium alloys (AZ91D, LAE442) were used in this study. Standardized immersion and electrochemical tests according to ASTM standards were performed. The in-vivo corrosion tests were carried out by intramedullar implantation of magnesium alloy rods into guinea pig femura. Animal studies were performed according to a governmental approved protocol. Following fixation in paraformaldehyde, the specimens were scanned in a microtomography device utilizing synchrotron radiation at the Hamburger Synchrotronstrahlungslabor HASYLAB at Deutsches ElektronenSynchrotron DESY (Fig. 1). At beamline W2, the specimens were imaged by attenuation microtomography using a photon energy of 31 keV. Exposed to the parallel X-ray beam, the sample was precisely rotated stepwise 0.25° in the angular range 0-180°. After each step the absorption image was recorded [3]. The specimens were investigated in five different positions of the z-axis to obtain a high spatial resolution. Further, these separately reconstructed datasets were finally stacked to form an entire dataset. The voxel edge size of the tomogram was 10 μm. The residual implant volume was analyzed using VGStudio Max 1.2® software. Absorption tomography produces 3-D images of the linear Xray attenuation coefficient μ l. The attenuation of the X-rays passing through a material can be described using the equation