| Summary: | 碩士 === 國立臺灣科技大學 === 機械工程系 === 106 === The stent retriever is a fish basket type metal stent and mainly used for dealing with ischemic cerebral stroke caused by blood vessel obstruction. The stent can grasp the blood clot that blocks the artery to the catheter, then the clot is taken out of the body with the catheter. The main commonly used material is Nitinol, due to its shape memory property and good biocompatibility.
The main purpose of this thesis is to improve two parts of the post laser cutting process in stent fabrication: sandblasting and electropolishing. The first is to improve the shortcoming of conventional mechanical sandblasting, which often results non-uniform stent material removal due to its hand-held method. Therefore, the newly developed rotary slurry grinding method was performed in this study. In the method, stents were fixed on a special fixture and immersed in the slurry to perform rotary grinding with a controllable DC motor. The surface morphology and slag removal of the stent model were investigated with increasing working time under different particle sizes. Finally, the effect of process time and power source type of electropolishing process on edge rounding was studied. Experiments were carried out by varying time of electropolishing work to observe the relationship between the material removal amount and the change of edge rounding. In addition, a pulsed DC power supply was used, compared with a DC power supply, to study its effect on the material removal rate and edge rounding performance in the stent electropolishing process.
The experimental results indicate that the rotary slurry grinding with the coarse abrasives (size 87.5~73.5μm) firstly and the medium abrasives (size 62~52.5μm) secondly can completely remove the slag generated by laser cutting, and obtain better surface topography quality. In the study of edge rounding, it is observed that the increase in the material removal can improve edge rounding. The study of pulse electropolishing has proved that it can improve the drawback of conventional DC electropolishing, to achieve edge rounding and sacrifice the material usage. The similar edge rounding value can be achieved with pulse electropolishing process and the material removal amount is about 3% less.
Keyword: stent retriever, rotary slurry grinding, pulse electropolishing, edge rounding
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