Research On Degradation Behavior And Biocompatibility In Vitro Of Mg Alloys For Cardiovascular Stent Application

Artificial implants are needed to help restore bone trauma or cardiovascular stents more than 50 million people around the world year by year.Non-degradable stainless steel,nickel-titanium alloy or cobalt-chromium alloys are usually used for human implantable stents which are being in the body for a long time and not conducive to tissue repair and physical examination.Thus,the use of degradable metal to prepare cardiovascular stents has become the focus of research.On the one hand,no surgical removal is required to relieve the pain of the patent?s two surgeries.On the other hand,the degradable implant material release specific ions,which can induce cell proliferation,tissue regeneration and achieve self-repair.The materials required for the implantable stent of the human body are relatively high.it is required to have good strength,toughness,corrosion resistance and biocompatibility at the same time.Magnesium alloys are expected to be a degradable metal material suitable for cardiovascular stents due to their excellent biocompatibility and elastic modulus.In the early stage,our group developed magnesium alloy with excellent mechanical properties.Its strength and plasticity meet the requirements of vascular stent application.However,the degradation behavior of magnesium alloy as a cardiovascular stent needs a lot of research.Blood compatibility and cell compatibility experiments are needed to test its safety and effectiveness before clinical use at the same time.Therefore,this paper focuses on the degradation mechanism and biocompatibility in vitro of magnesium alloys for cardiovascular stents.In this paper,Mg-2Y-1Zn-0.4Zr and Mg-1Y-3Zn-0.6Zr-0.5Ca alloy compositions were designed.The as-cast alloys were separately subjected to extrusion and solution aging treatment to obtain magnesium alloys with different microstructures.The degradation properties and biocompatibility of the alloys were investigated by microstructure,electrochemical corrosion,weight loss,blood compatibility and cell compatibility.The degradation mechanism of magnesium alloy in simulated body fluid?SBF?environment was studied,and the interaction mechanism between degradation rate and tissue microenvironment was determined.The research results are as follows:?1?Microstructure evolution of two different components of magnesium alloys in different states:the phase composition of the Mg-2Y-1Zn-0.4Zr is mainly?-Mg and Mg₃YZn₆.The phase composition of the as-cast and the as-extruded Mg-1Y-3Zn-0.6Zr-0.5Ca alloy is mainly?-Mg,Ca₂Mg₆Zn₃,MgZn₂and Mg₃YZn₆.After heat treatment?T4?,the second phase of Ca₂Mg₆Zn₃,MgZn₂ and part of Mg₃YZn₆ is dissolved into the matrix.?2?Corrosion mechanism of magnesium alloy in SBF:the potentials of Mg₃YZn₆,Ca₂Mg₆Zn₃ and MgZn₂ phases are higher than the magnesium matrix potential,forming corrosion galvanic couple with magnesium matrix.The phenomenon causes the corrosion rate of magnesium matrix around the second phase to accelerate,resulting in second phases peeled off to form a corrosion pit.The experimental results show that the as-extruded Mg-2Y-1Zn-0.4Zr alloy and the as-extruded Mg-1Y-3Zn-0.6Zr-0.5Ca alloy have good corrosion resistance.?3?Relationshipbetweendegradationrateanddifferentcell microenvironment:degradationrateofdifferenttreatmentstates Mg-2Y-1Zn-0.4Zr alloys and Mg-1Y-3Zn-0.6Zr-0.5Ca alloys in physiological saline and culture fluid is different.Thus,the concentration of magnesium ions in the extracts is different.The experimental results show that the as-extruded Mg-2Y-1Zn-0.4Zr alloy and the as-extruded Mg-1Y-3Zn-0.6Zr-0.5Ca have good blood compatibility and cytotoxicity.?4?Tolerance of different concentrations of magnesium ions to different cell types:When the magnesium ion concentration is higher than 6.16mmol/L,the cell morphology of mouse fibroblast L929 changes,and the survival rate decreases.When the magnesium ion concentration is higher than 12.25mmol/L,the cellular activity of murine bone marrow mesenchymal stem cells began to decrease.