The Influence of Double Extrusion Process on the in-vitro Dynamic Degradation Properties and Biocompatibility of Mg-Zn-Zr Mini-tubes

Abstract

According to the statistic reports from WHO on 2011 cardiovascular diseases (CVDs) are the number one cause of death (31%) in non-communicable diseases globally Among them the coronary artery clogging plays the most significant role due to cholesterol pileup Clinically balloon angioplasty combined with stent implantation (60%) is performed to effectively maintain the blood flow Traditionally 316L stainless steel titanium and Co-Cr alloys are widely used However they have some inherent disadvantages that restrict their widely use and most importantly about 25% of patients suffered from restenosis Also being clinically proven the self-healing of the vessel is about 6~12 months thus the investigation of biodegradable stent is necessary Magnesium alloy has its unique advantages to become the biodegradable material as a stent Adequate high strength and most importantly excellent biocompatibility make it highly attentioned However the obstacle that researchers are facing is the high degradation rate of magnesium alloy in human body which may not be able to catch up with the healing rate of surrounding tissue In this study magnesium mini-tube that fits the diameter of cardiovascular stents was successfully made using double extrusion methods by semi-continuous process The influence of extrusion ratio temperature extrusion speed on microstructure were examined Accompanied with electrochemical test dynamic corrosion test and biocompatibility test the best criterion among low extrusion ratio double extrusion process was defined It not only preserved homogeneous fine grain structure with 2μm of grain size but also containd 350MPa yielding strength and nearly 12% elongation property Most importantly the results of dynamic corrosion rate was excellent coming to average value of 1 mmy-1 after 14 days which was even better than the static corrosion rate of other reports Nonetheless the cytotoxicity test and hemolysis test also proved the nice biocompatibility of ZK60

Date of Award	2016 Nov 17
Original language	English
Supervisor	Ming-Long Yeh (Supervisor)