| Summary: | 碩士 === 國立中興大學 === 材料科學與工程學系所 === 102 === Some limitations like the hypersensitivity reaction, the long-term impairment of endothelial response, and the late stent thrombosis for drug-eluting stents using percutaneous transluminal coronary angioplasty (PTCA) are still found. Though the degradable magnesium alloy used to construct an absorbable stent could be another candidate, the poor corrosion resistance is relatively a serious impediment against wider applications of magnesium alloys. In this study, the coatings of zirconia (ZrO2) bottom layer and calcium phosphate (CaP) top layer are carried out on pure magnesium specimens by electrochemical 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 system (FIB), 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/ZrO2 coated magnesium specimens are potential for biodegradable cardiovascular stents.
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