Applied Research On Mechanical And Degradation Properties Of Monofilaments Used In Plla Braided Stents

At present,the main treatment for vascular diseases is vascular stent implantation.The problem faced by traditional metal stents is that the stents will remain in the body permanently after vascular remodeling,which causes many complications and makes follow-up treatment difficult.Biodegradable stents are committed to solve this problem.Poly(L-lactic acid)(PLLA)has become a common material for biodegradable stents due to its superior biocompatibility and mechanical properties.PLLA stents need to increase the strut thickness or monofilament diameter in order to provide sufficient mechanical properties,which may cause a series of problems such as inflammation.This thesis aims to improve the mechanical properties of the PLLA braided stents,and taking PLLA monofilaments as the research object.The key processes affecting the mechanical properties of PLLA monofilaments are discussed,and the mechanical properties of the PLLA braided stents are improved.Main research results of this thesis are as below:(1)The problems faced by PLLA braided stents were summarized and analyzed,and the viewpoint of improving the mechanical properties of braided stents by improving the properties of PLLA monofilaments was put forward.The effects of crystallinity,molecular weight,and polymer orientation on the mechanical properties of PLLA monofilament were analyzed from the perspectives of the physicochemical properties and internal structure,which provided a theoretical basis for the subsequent experiments and the ideas for improving the mechanical properties of PLLA monofilaments.(2)In view of the material factors affecting the mechanical properties of PLLA,two kinds of processes to improve the mechanical properties of PLLA monofilament were proposed:solid-state drawing and annealing.The effects of different draw ratios and annealing methods on the properties of the monofilament were compared,and the evolution models of the internal structure of the monofilament in solid-state drawing and annealing were established based on the experimental data.(3)Degradation experiments were carried out to study the degradation performance of the monofilaments.Degradation experiments of monofilaments were carried out in PBS solution at 37℃.The changes of physicochemical properties and mechanical properties of PLLA monofilaments at different degradation stages were studied,which provided a preliminary theoretical basis for the degradation of PLLA braided stents in vivo.(4)To explore the application of solid-state drawing and annealing in the braided stents,the solid-state drawn monofilaments were braided into spiral structures and stents.Through the measurement of the mechanical properties of spiral structures and stents,the potential application of different annealing methods in braided stents was analyzed,and the effectiveness of solid-state drawing process to improve the mechanical properties of braided stents was discussed.