Corrosion Effects of Electrolytic Biocomposites Coated Magnesium on Endolithial Cell Viability

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.