The effects of cells on biocrrosion of Mg alloys

Abstract

Event Abstract Back to Event The effects of cells on biocrrosion of Mg alloys Akiko Yamamoto1 and Akemi Kikuta1 1 National Institute for Materials Science, Biomaterials Unit, International Center for Materials Nanoarchitectonics, Japan Recently, biomedical application of magnesium (Mg) and its alloys are intensively studied for realization of biodegradable metallic devices such as bone fixture and cardiovascular stents. For the success of these devices, control of their degradation rate in the human body is a key issue since it critically influences the mechanical integrity and biocompatibility of these devices during implantation period. Body fluid contains inorganic ions as well as organic compounds such as amino acids and proteins. We have already reported the accelerating and inhibiting effects of amino acids and serum proteins on the degradation of pure Mg under cell culture condition[1]. Implanted devices are also facing to surrounding tissues and cells. Therefore, the degradation of Mg alloys can be influenced by the surrounding tissue and cells due to their metabolic activities and specific microenvironments. In this study, the effect of living cells cultured on Mg alloy substrate on the substrate degradation is examined by electrochemical measurements. Rolled sheet of Mg-3wt.%Al-1wt.%Zn (AZ31) alloy is employed in this study. The plates of 15 mm square and 0.5mm in thickness were prepared. Every surface of the plate was polished with #600 (14 µm) SiC paper in ethanol, and then, ultrasonically washed and sterilized with acetone for 5 min. In vitro degradation behavior of these plates was studies with and without culturing cells (murine fibroblasts L929) in Eagle’s minimum essential medium supplemented with 10% fetal bovine serum (E-MEM+FBS) under cell culture condition, i.e., 37˚C and 5% CO2 in humidified air. A standard three-electrode system was employed; an AZ31 alloy sample (exposed area of 0.950 cm2) as a working electrode, Ag/AgCl (3M NaCl) as a reference electrode, and a platinum mesh as a counter electrode. Electrochemical impedance spectroscopy (EIS) was performed under following conditions; at open circuit potential (OCP), 5mV, 0.01~105 Hz after 2, 6, 12, 24 and 48h of incubation. Potentiodynamic measurement was carried out after 48h of incubation at the scanning rate of 0.5mV/s and OCP-0.25V to -1.2V. Fig.1 shows typical EIS results of AZ31 alloy samples with and without cells. The equivalent circuit model used to analyze EIS spectra and resulting polarization resistance (Rp) were shown in Fig.2. Rp was calculated by adding Rfilm and Rct. Rp without cells increased along the incubation period whereas Rp with cells decreased after 6 h. The polarization curves of AZ31 with and without cells after 48 h of incubation were shown in Fig.3. Current density of AZ31 with cells tended to be higher than that of without cells. The pH of the medium after 48h-incubation with and without cells was 7.58 and 7.39, respectively. This slightly lower pH for the sample with cells probably causes the reduction of Rp. Obtained data revealed the accelerating effect of cells on the biodegradation of AZ31. This acceleration effect of cells on the degradation of Mg alloy substrate is also confirmed by Mg-Ca alloy, with the observation of localized corrosion around cell colony formed on the sample surface[2]. This work was supported by JSPS KAKENHI Grant number 26282151.