Study On Micro Injection Molding Technology Of Biodegradable Stent

Biodegradable and polymeric stent is the most potential development direction of stent, which not only has good biological compatibility, but also can be degraded into carbon dioxide and water after a temporarily supporting vessel wall. It has no stimulation to the human body, can reduce the incidence of thrombosis and restenosis, and is able to provide better treatment to keep morbid vascular open. At present, the stent relys mainly on laser processing to manufacture. Although laser processing can ensure the complete structure of stent, it has influence on heat affected zone. The production efficiency and yield are lower, which leads to the high price of stent. Therefore taking biodegradable and polymeric stent as the main research object, this dissertation carried out more comprehensive exploration and research on biodegradable materials of stents, structure, technology of the injection mold design and processing.First of all, the biodegradable and polymeric material (modified polylactic acid) of stent was studied in this paper. The material properties, mechanical strength, rheological properties of modified polylactic acid were studied mainly in three aspects:the DSC thermal analysis, tensile test and rheological properties. Research shows that crystallized modified polylactic acid materials can be fully obtained by a certain cooling speed rate, which can achieve relatively better mechanical properties. In the early stages of the shear rate increasing, the shear viscosity of modified polylactic acid materials relates to temperature, as the shear rate increases, impact of temperature on the shear viscosity decreases gradually.Secondly, the expansion process of stent was simulated and analyzed by using the finite element method. According to the technical requirement of stent design, a new structure for stent was proposed, which use the finite element method and computational mechanics to analyze the expansion process. By comparing with the expansion characteristics of metal stent, the expansion performance of poly (lactic acid)(PLA) material stent was explored and analyzed. Based on the research results, it can be seen that the support unit of stent with concave type not only has better relative deformation, but also has a better uniform expansion character, which can effectively inhibit the uneven expansion in the process of stent. Compared with metal stents, the biodegradable poly (lactic acid)(PLA) stent has better flexibility and uniform expansion, but the elastic resilience need to be further improved. Thirdly, according to the structure of the proposed biodegradable stent, the micro injection molding mold was designed. Taking structural characteristics and design technology of micro small plastic injection mold of stent into consideration, the overall structure and opening process of the mould were analyzed to determine the structure of stent micro injection mold, and stent micro injection mold was designed in detail.Finally, the micro injection mold of biodegradable stent was achieved by adopting reasonable micro machining and precision machining technology, and injection molding experiment was carried out. First of all, the precision and high precision processing equipment was used to manufacture the micro injection molding of stent mould. Second, the relationship between fill rates of stent and the different melt temperature, injection pressure and mold temperature was studied. The results show that the melt temperature, injection pressure and mold temperature are important process parameters in injection molding of small and thin part, and have a positive correlation of the fill rates of stent.