Study On Four-axis 3D Printing Technology For The Fabrication Of Polymer Stents

As new generation of coronary stents,biodegradable polymer stents,with their unique biodegradability and biocompatibility,could effectively solve restenosis of coronary arteries after interventional therapy,which has received intensive attention and study.However,some fabrication problems of the stents,such as destruction of material bioactivity,low surface quality of stents,lack of flexibility,and high price,are still unsettled.It is noteworthy that 3D printing technology,by virtue of its striking advantages of additive manufacturing,has displayed great potentials in the manufacture of personalized biomedical devices in the past years.Both of stent design and manufacture will directly determine the final performances of the stents.Therefore,taking the polymer stents as the research object,this dissertation designed a new stent structure,analyzed the stent's expansion performance,adopted a novel four-axis 3D printing technology fabricating the stent,and investigated the molding experimental process.The main work of the paper is as follows:Firstly,an exceeding polymer vascular stent structure was put forward.The asymmetrical support units of the stent are made of two rectangular rib section sine curves ribs that contact at the apex,so the stent owns good radial support capacity in the case of smaller rib thickness.The Z-design in link units could effectively increase the flexibility of the stent.Besides,the influence of length changes of the support units on the stent's radial recoil and foreshortening ratio in the expanding process of a balloon-stent analysis model was explored by the finite element method.The results showed the stent structure displayed good expansion performances and by increasing length of the support units,radial recoil rate decreases but foreshortening ratio increases;besides,Von Mises stress slightly decreased.Secondly,in terms of special structures of the polymer stents,a novel four-axis 3D printing method based on the principle of Fused Deposition Modeling was firstly proposed.The four axis 3D printer is characterized by adding a rotating shaft with controllable motion and temperature based on common Descartes printer structure,so it has unparalleled advantages in fabricating special complex mesh thin-walled tube structures.And the full design of the fouraxis 3D printer was carried out in the paper and it successively introduced the printer's mechanical structure,control systems hardware and software in detail.In the end,the physical printer was fabricated.Then,with regard to the specific features of four-axis linkage 3D printing technology,the factors causing principle manufacture errors and technical errors were deeply analyzed.Their theoretical forming mechanisms were clearly illustrated.In the end,the corresponding improvement measures,such as improving manufacture and assemble accuracy of the printer,decreasing chord heights in the format conversion,and choosing suitable printing parameters,were respectively put forward.These work provided a theoretical basis for subsequent forming experiments.Finally,numerous manufacturing experiments of the stents on the four-axis 3D printer were conducted and the stent products exhibit good qualities,which validated the feasibility and effectiveness of four-axis 3D printing technology in manufacturing polymer stents.Furthermore,it was analyzed and discussed that how three significant process parameters,printing speed,print temperature and layer thickness,affects dimensions and radial support capacity of the stent printed.The results showed that these three parameters had significant influences on circumferential dimensions and radial support capability.