The Study Of New Biodegradable Intravascular Stents

1. To investigate the effect of the molecular weight of a PLLA thin film on the mechanical property thereof and the possibility of preparing new type of biodegradable intravascular stents (BIS) with advanced computer aided design (CAD) and laser engraving. To determine the difference between the mechanical properties of new shackle shape BIS, zigzag shape BIS, spiral shape BIS and metal stent. To develop the release device of the new shackle shape BIS.2. To investigate the biocompatibility of the new shackle shape BIS, and evaluate the histopathological findings according to a fixed timetable after implanting the shackle shape BIS so as to determine the possibility of implanting it into vessels. And to investigate the evolution of the vascular endothelial function shortly after implanting the new shackle shape BIS.Materials and Methods1. Five PLLA thin films with molecular weights of 50,000,150,000,300,000 and 500,000 respectively were prepared with solvent evaporation method and the mechanical properties of the PLLA thin films were tested. Fifteen shackle shape BISs, fifteen spiral shape BISs, and fifteen zigzag shape BISs were respectively prepared by using the PLLA thin film with molecular weight of 300,000 and their mechanical properties were tested and compared.2. The prepared new "shackle" shape BISs were implanted into the iliac arteries of pigs. CT and ultransonic examinations were performed on the pigs according to a fixed timetable to observe the stents and the arteries. The animals were euthanized according to a fixed timetable for histopathological assessment. Blood were extracted from the pigs according to a fixed timetable to test the biochemical criteria IL-1,6-k-PGF1a, ET-1, TNF-a and IL-6 of the vascular endothelial function so as to analysize the evolution of the vascular endothelial function after implanting the "shackle" shape BISs.Results1. The "shackle" shape BISs meet the requirement of the mechanical properties of an intravascular stent and are superior to the spiral shape BISs and the zigzag shape BISs in their mechanical properties.2. Twenty "shackle" shape BISs were successfully implanted into the iliac arteries of sixteen pigs. The "shackle" shape BISs were confirmed to have no displacement by using radiological examinations, the arteries were neither obstructed nor narrowed, and no servere inflammatory reactions were observed. The "shackle" shape BISs were not completely degraded twelve months after the implantation. The biochemical criteria IL-1,6-k-PGF1a, ET-1, TNF-a and IL-6 of the vascular endothelial function have a trend of decrease after an increase. The criteria are different at different time and thus are meaningful in statistics. Especially, the criteria IL-1,6-k-PGF1a, ET-1 and TNF-a have a peak seven days after the implantation. And each of the criteria tended to be recovered two months after the implantation.Conclusion1. The new "shackle" shape BISs meet the requirement of the mechanical properties of an intravascular stent, are superior to the spiral shape BISs and the zigzag shape BISs and are equivalent to the metal stents in their mechanical properties. The new "shackle" shape BISs can meet the requirement of implantation.2. The new "shackle" shape BISs are convenient to be released and deployed. After being implanted into arteries, the BISs do not induce severe inflammatory or foreign body reaction. At the 8th week, the BISs were covered completely by neointima, and after the 8th week the growth of the neointima slowed down. The "shackle" shape BISs were not completely degraded twelve months after the implantation. After implanting the "shackle" shape BISs, the biochemical criteria of the vascular endothelial function have a trend of decrease after an increase. The criteria tended to be recovered two months after the implantation. The "shackle" shape BISs have reliable mechanical strength and good biocompatibility, although further study are needed to determine when they can be completely degraded.