Corrosion Effects of Electrolytic Biocomposites Coated Magnesium on Endolithial Cell Viability

Abstract

Though the degradable magnesium alloy used to construct an absorbable stent could be another candidate, its poor corrosion resistance is relatively a serious impediment against wider applications of magnesium alloy[1]. In this study, the coatings of zirconia (ZrO2) bottom layer and calcium phosphate (CaP) top layer are carried out on pure magnesium specimens by electrolytic deposition and subsequent annealing, leading to the corrosion current density reduced from 13.3 to 3.86 μA/cm2 derived by potentiodynamic polarization tests in artificial blood plasma at 37 °C. Furthermore, calcium phosphate (CaP), gelatin (Gel) and heparin (Hep) are co-deposited on post CaP/ZrO2 coated specimens in order to fabricate the heparin sustaining release system for promoting the hemocompatibility of magnesium. Heparin loaded composite coatings are analyzed by X-Ray diffractometry (XRD), field emission scanning electron microscope (FESEM), focused ion beam (FIB) system, toluidine blue colorimetric assay, UV-visible spectrometer, and indirect endothelial cell viability tests. The drug content increases from 243.56±55.18 μg/cm2 for single layer (CaP-Hep) to 484.19±19.26 μg/cm2 for multilayer (CaP-Gel-Hep/CaP-Hep/CaP/ZrO2) and the sustaining release of the latter lasting for more than 28 days compared with that of the former for 1 day in PBS solution. The cell viability, related to Mg2+ ions in medium extracts which are still toxic to endothelial cells at high concentrations, is 63 % for the uncoated, 97 % for the ZrO2 coated, and 110 % for the CaP/ZrO2 and CaP-Gel-Hep/CaP-Hep/CaP/ZrO2 coated specimens compared with 100 % for the negative control. All results indicate that ZrO2 coated, CaP/ZrO2 coated, and CaP-Gel-Hep/CaP-Hep/CaP/ZrO2coated magnesium specimens are potential for biodegradable cardiovascular stents. Acknowlegement The authors are grateful for the support of this research by the National Science Council,Republic of China (Taiwan) under contract No. NSC 102-2221-E-005-027-MY3. [1]M.J. Wang, C.F. Li, S.K. Yen, Electrolytic MgO/ZrO2 duplex-layer coating on AZ91D magnesium alloy for corrosion resistance, Corrosion Science, 76 (2013) 142-153.