Artificial Anal Sphincter using Shape Memory Alloys

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Following results and achievements have been attained in this project.1)In the first fiscal year of the project, we established the protocol of animal experiments for colostomy with piglets, implanted prototypes of the artificial sphincters under the stomas, and were successful in short-term animal experiments in the respects of basic functions : the closing and opening functions of the device.2)The second year of the project was devoted to the development of a transcutaneous energy transmission system and overheating prevention equipment in order to realize a complete implantation of the device. Animal experiments with periods of up to 4 weeks were carried out using these equipments. The healthy situation of the animal (piglet) in these experiments was confirmed. Moreover, ordinary evacuation was observed almost each time when the artificial sphincter was activated in open.3)The optimum design about the dimension and shape of the artificial sphincter was conducted. With the improved prototypes implanted into animals, the monitoring of the inner pressure was carried out with a pressure sensor inserted in the closed intestine. It was found that with the occlusion pressure ranging from 50 to 60mmHg, the device had sufficient closing function without any damage of ischemia.4)As a result of the careful design of the overheating protection and thermal insulation in materials and dimension, even when artificial sphincter was heated to open for a period longer than 10 min., it was able to control the temperature of its surface in contact with surrounding tissues to be lower than the maximum allowed temperature of living tissue,40℃.The occlusion pressure and surface temperature of the device are two most important criterions in the assessment of the device. The success in solving these two problems in this project will facilitate the commercialization of the device in near future.