Research On Equipments And Technics In Polymer Coating Preparation Of Drug Eluting Intravascular Stent

The achievement of a hospitable relationship between stent, coating matrix, drug, and vessel wall is extremely challenging, so it is necessary that all the relevant knowledge should be applied comprehensively to solve the varied problems that would occurred in the process of developing DES. In formulation of a successful drug-eluting stent, there are generally three chief problems, including the coating matrix, the method of coating, and the screen, adherence, and release of biological agent, which should be solved. In order to develop the drug eluting stent, the domestic-made 316L Stainless Steel intravascular stent was used as stuff , and the L-polylactic acid (L-PLA) and poly DL-lactide-co-glycolide acid (PLGA) were used as coating matrix. The spray method based on ultrasonic atomization and HVLP were used to prepare Polymer-coated stent, which could be immersed in the drug solution to absorb the biological agent.At first, the spray equipment for experiment was designed and produced according to the character of spray process. The principle of ultrasonic atomization was used to design the ultrasonic atomization equipment in forepart. This equipment was composed of four parts, which including atomization module, gas-carrier module, solution-container module, and stent-carrier module. The atomization module could atomize the polymer solution through the 30WS Drop-In ultrasonic atomizer located in the cylindrical water container. The gas-carrier module could control and adjust the outflow flux of N2 in the high-pressure air tank through gas reductor. The polymer-solution container and nozzle were all made of glass that was beneficial to the atomization of polymer solution and the out-spray of atomized polymer. The stent-carrier module helped to prepare uniform polymer coating by the means of making the stent move back-and-forth in front of nozzle at the time of maintaining circumrotation. The principle of HVLP was used to improve this equipment in rare part. The improved equipment was also composed of four parts, which including gas-carrier module, solution-container module, spray nozzle and stent-carrier module. Two levels of gas redactors were used to control gas pressure precisely. Stepper motor and micro pump could control the solution flux precisely. The nozzle used the principle of inside-mixed atomization to reduce its own volume.Secondly, chromic acid lotion was used to pretreat surface of bare 316L SS stent. The oxidation degree of the surface in different time were compared to choose the best pretreatment art. The stent surface morphologies were visualized through scanning electron microscopy (SEM), energy dispersive X-ray spectrometry (EDS), contacting angle meterage and atomic force microscope (AFM) were used to confirm surface effects of 316L SS stent that pretreated by the pretreatment art.Finally, the technological process was introduced in this text. The optimal parameters, which were determined by measuring the thickness of matrix coating through the metallurgical microscopy(MM), were initialized to prepare the polymer coating whose morphologies were examined both pre- and post-expansion in vitro. The stent surface morphologies were visualized through Optical microscope (OM), scanning electron microscopy (SEM), and scanning probe microscope (SPM). The characters of post-expansion could be determined through judging there were cracks, break-off, or turnup on the stent surface or not.The experimental result revealed that the acid pretreatment techniques can rough surface of bare 316L SS stent tinily. The surface roughness was influenced by the acid lotion and the treat time. The spray equipment and technological process for experiment could be applied for preparing polymer matrix coating of drug eluting stent, but the roughness and thickness of matrix coating was influenced by the proportion of polymers, the chroma of polymers, the air pressure, and the duration of spraying.