The application of electro-etching in the manufacturing process for cardiovascular stents
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The objective of this project is to investigate and develop suitable surface treatment methods applicable to bio-medical devices. In particular, attention is focused on incorporating the electro-etching procedure into the manufacturing process for cardiovascular stents. The project aims to replace the currently preferred chemical etching procedure with electro-etching. At present, the surface treatment processes incorporates: chemical etching followed by ultrasonic agitation in a purified water bath, and by electro-polishing. The Taguchi Method is applied to identify the optimum parameter settings in the electroetching process. These parameters include: time, temperature, potential difference between electrodes, acidity level of electrolyte and the amount of agitation applied to the electrolyte by stirring. The experimental equipment employed to determine the optimum electro-etching parameters include: low-noise DC power supply, fumehood, electroetching unit with electrodes and ultrasonic bath. The optimised electro-etching process has been incorporated into a manufacturing production line with great success. The overall duration of ultrasonic agitation during the entire manufacturing process of stents is decreased by 37% using the electro-etching. Exposure to ultrasonic waves decreases the subsequent fatigue life of the delivered product. Therefore the reduction in exposure to ultrasonic waves by 83.3% is of considerably benefit. A comparison study between the surface finish obtained using the chemical and the new electro-etching processes has been completed using Scanning Electron Microscope and Atomic Force Microscope. This study shows dimensional variation of ±0.00559 mm between struts thicknesses of stents treated by the two methods, while similar roughness values (Ra=0.23(J,m) are computed. The electro-etched stents have passed all visual and dimensional inspection procedures. The research presented in this thesis clearly demonstrates and quantifies that the electro etching process generates similar surface finish to the chemical process of etching.
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