Development of an Implantable Artificial Anal Sphincter Using a Shape Memory Alloy

Background/Purpose: The authors created a new artificial anal sphincter using a shape memory alloy (AS-SMA) to treat fecal incontinence and evaluated its validity. Methods: AS-SMA consists of 2 Ti-Ni plates to sandwich the intestine and generates a pressure of 55 mm Hg at its resting position. With the electric power supply, the 2 metals bend to form an almondlike shape making a maximum gap of 33 mm between each other at the temperature of 55°C. The device was attached to the colostomy in a piglet and was operated several times a day for 1 month. Fecal continence, bowel movements, and general condition of the piglet were recorded. After the experiment, tissue damage around the device was investigated. Results: Fecal continence was obtained while the device was in the resting position. When it was operated, bowel movements were observed. The bowel movements to operations ratio was 82:105 (78%). During the experiment, the animal had neither abdominal distension nor vomiting. At the autopsy, there was mild inflammation and shallow burns around the device. No compression injury was detected. Conclusions: AS-SMA achieved fecal continence of the colostomy. With reduction of the associated side effects, it would be a potential substitute for an impaired anal sphincter.