| Introduction:Endovascular stent placement is an important and effective treatment for peripheral arterial disease（PAD）.As a new type of scaffold that can be absorbed in the human body,bioresorbable vascular scaffold（BVS）has the potential to solve long-term side effects such as chronic vascular inflammation,intimal hyperplasia,and stent thrombosis,which are caused by traditional stent placement.Metal BVS has better mechanical performances than polymer BVS with the same thickness,which is beneficial to make the vascular scaffold thin and light,reducing both the metabolic burden of the body and the interference to the blood flow.However,magnesium（Mg）alloy BVS,which is widely used in clinical metal BVS,always faces the challenge of rapid degradation rate,while iron（Fe）alloy BVS still has the problem of slow degradation rate.Compared with Mg,because of the better strength and plasticity,Fe can greatly reduce the thickness of the stent wall,reducing the metabolic burden,which makes it the implantable and degradable metal materials with great potential.However,as a degradable material,Fe still has the problem of slow degradation.How to greatly improve the degradation rate under the premise of maintaining sufficient mechanical properties has always been a major problem,and it is urgent to conduct in-depth research on material design and preparation.Alloying is an effective solution.Manganese（Mn）,as an indispensable trace element in the human body,is a suitable alloying element.The degradation rate can be significantly increased by FeMn binary alloying.Many studies have shown that FeMn alloy have good mechanical performance,biocompatibility and nuclear magnetic resonance compatibility,and the degradation rate is controllable.The mechanical properties and degradation properties of FeMn alloy have been thoroughly studied.However,most of its biocompatibility studies only evaluate the cytotoxicity in vitro.More systematic and in-depth biocompatibility studies are needed.The ternary FeMnC alloy obtained by adding carbon（C）element may further improve the mechanical properties and degradation rate,and will have a broader clinical application prospect.Traditional vascular stents currently in clinical use are mostly prepared by laser engraving technology or wire braiding technology.These two processes still have problems,such as difficult preparation of capillary materials,imperfect processing technology,immature material development and extreme dependence on imports,both of which have defects such as high production cost,long cycle,and large equipment investment,etc.Moreover,core technologies such as design and preparation process are mostly controlled by foreign pharmaceutical technology companies,without core intellectual property rights,resulting in high costs and prices of vascular stents,belonging to the monopolized"bottleneck"technical problem in China.Therefore,it is necessary to develop a new stent preparation technology,which can not only ensure product performance,but also avoid complicated processes,improving productivity and reducing production costs.The new manufacturing technology of vascular stent-metal injection molding（MIM）technology has the advantages of preparing parts with high shape complexity,small size and excellent performance in a short time and on a large scale,which can ensure product quality and greatly reduce the production cost.However,these characteristics of MIM technology have not been sufficiently developed in vascular implant materials.In view of the above series of problems,this study is guided by the cutting-edge BVS needs in the field of vascular interventional medicine,and intends to prepare new FeMnC alloy and scaffold through MIM technology,and evaluate the mechanical properties,biocompatibility,degradation performance,efficacy and safety of FeMnC alloy BVS through in vitro and in vivo experiments on cells,blood,tissues,organs and animals.In this study,MIM technology was applied to stent preparation,which innovated stent manufacturing technology,and is expected to be a complementary or even alternative technology for laser engraving technology and wire braiding technology in the field of vascular stent preparation,providing a new treatment strategy for PAD.Methods:（1）In this study,FeMn alloy was prepared by MIM technology,and the element content,density and mechanical performance of FeMn alloy were tested,and the microscopic characterization was observed.（2）Primary human umbilical vein endothelial cells（HUVECs）and primary human aortic smooth muscle cell（HASMCs）were cultured in vitro.The cytocompatibility of FeMnC alloy was investigated by analyzing cell proliferation,migration,adhesion,apoptosis,cytoskeleton morphology,tube-formation and expression of cell inflammatory factors with western blot.At the same time,subcutaneous embedding FeMnC alloy models were constructed in rats.Hematoxylin-eosin（HE）staining and Prussian blue staining,and alloy corrosion products were characterized and analyzed to further explore the tissue and organ compatibility and speculate the possible corrosion products.（3）FeMnC alloy BVS was prepared by MIM technology,and a series of post-treatment of the scaffold were carried out,including the detection of the radial support strength of the scaffold,the characterization of the size,the optimization of the polishing process,etc.,to explore the overall performance of FeMnC alloy BVS.（4）Biodegradable FeMnC vascular scaffold was compared with non-biodegradable 316L stainless steel vascular stent through animal experiments to evaluate the implantation efficacy and safety,mechanical performance,tissue and organ compatibility,and degradability of biodegradable FeMnC vascular scaffold.Results:（1）With the increase of sintering pressure to 5 atm and carbon content of 0.5 wt.%,the density of FeMnC alloy increases to 97%,the tensile strength increases to 778 MPa,the yield strength increases to279 MPa and the elongation rate increases to 35%.（2）10%extract of FeMnC alloy could slightly inhibit cell proliferation of HUVECs（80.6%vs 100%,p<0.001）,but had no significant effects on cell migration,adhesion,tube-formation and expression of inflammatory factors（vascular cell adhesion molecule-1,intercellular adhesion molecule-1,CD62E-selectin and Interleukin-1β）of HUVECs（p>0.05）.10%extract of FeMnC alloy can inhibit the 24 h migration of HASMCs（38.5%vs60.5%,p<0.001）,but has no significant effect on cell proliferation,adhesion,cytoskeleton morphology and apoptosis of HASMCs（p>0.05）.（3）The hemolysis rate of FeMnC alloy is only 0.65%,far lower than the5%required by the national standard.Compared with 316L stainless steel,FeMnC alloy can inhibit platelet adhesion and aggregation.In addition,FeMnC alloy has no significant effect on fibrinogen degradation product,thrombin time,prothrombin time,fibrinogen,D-Dimer,activated partial thrombin time and antithrombinⅢ（p>0.05）.（4）No significant morphological and pathological toxicological changes and immune cell recruitment were observed in the subcutaneous embedding model of rats.The weight loss rate of degradation for 90 days(1.72×10-4g/d)and 30days(3.58×10-4g/d),respectively,was significantly different from that of degradation for 7 days(8.79×10-4g/d)（p<0.001;p<0.001）.Energy dispersive spectrometer（EDS）and X-ray photoelectron spectroscopy（XPS）were used to analyze the surface elements of FeMnC alloy sheets in 1 week,1 month and 3 months.It was proved that the main components of the corrosion products were FeMn oxide and Ca/P product accumulation.（5）MIM technology can prepare biodegradable vascular scaffolds successfully.MIM technology combined with electrolytic polishing process and abrasive flow polishing process can better improve the surface quality and optimize the overall performance of FeMnC scaffold,and the characterization of scaffold size is stable.The radial support strength（k Pa）of the FeMnC scaffold was comparable to that of the 316L stainless steel stent（49.33 vs 57.33;p=0.268）.（6）The successful implantation rate of FeMnC scaffold placement was 100%,the survival rate of dogs was 100%,and no serious postoperative complications were observed.HE,EVG and Masson staining showed no significant abnormalities 1 month after surgery,and Prussian blue staining showed that trivalent iron ions penetrated into the whole layer of vascular wall.No significant abnormality of Fe and Mn ions was found in plasma,heart,liver,spleen,lung,kidney and brain by inductively coupled plasma-optical emission spectrometer（p>0.05）.HE staining of heart,liver,spleen,lung,kidney and brain showed no pathological changes.The EDS analysis of the surface products of the scaffold showed the increase of O elements and Ca/P elements,suggesting the formation of FeMn oxides and accumulation of Ca/P degradation products.（7）Micro-CT results indicated that the skeleton volume（mm3）of FeMnC scaffold 1month after implantation was reduced by 25.6%compared with that before surgery,and the difference was statistically significant（25.15 vs33.80,p<0.001）.However,during the degradation process,the whole structure was still intact,and there was no lumen collapse.Conclusion:（1）By increasing sintering pressure and carbon content,the densification of FeMnC alloy can be promoted and the mechanical performance was improved,so as to meet the clinical application requirements of degradable scaffold materials.（2）FeMnC alloy has good cytocompatibility,hemocompatibility,tissue and organ compatibility.（3）With the formation of FeMn oxides and the accumulation of Ca/P products,the degradation rate of FeMnC alloy decreased gradually with the longer the implantation time.（4）MIM technology innovation BVS manufacturing technology,combined with two step polishing process can better improve the surface quality of FeMnC scaffold and optimize the overall performance.The size of the scaffold characterization is stable and its radial support strength is comparable to 316L stainless steel stent.（5）FeMnC scaffold placement has shown good efficacy and safety in the early stage,and has good vascular compatibility and organ compatibility.（6）FeMnC scaffold had a good degradation rate in the early stage of placement,and its overall structure was still relatively complete and stable during the degradation process,and its mechanical performance could still meet the needs of continued application. |
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