Yasuyuki Kakubari

Preclinical development of SMA artificial anal sphincters

This article presents some progress in the development for preclinical trials of an artificial anal sphincter using shape memory alloys. The novel device has been proposed and developed by the authors group at Tohoku University. It has two dominant features different from other systems, which are either clinically available or still under development. One is that a solid driving element, a combination of shape memory alloy (SMA) ribbons and silicone elastomer sheets with a layered structure, is adopted for the opening and closing functions of the artificial sphincter. The other is a sandwich mechanism for the closing of bowel to reduce the risk of buckling induced ischemia which has been reported in hydraulically driven artificial sphincters with a radial squeezing mechanism. The device has fewer parts inside the body and therefore be implanted more easily. A new design eliminating the risk of heat burns enables long‐term implantation and brings the device closer to practical use. Functionality and safety of the device have been proved in three‐month animal experiments.

Temperature control of SMA artificial anal sphincter

In this article we used artificial sphincter utilising shape memory alloy (SMA) which consists of Ni and Ti. The anal canal is placed in between two boards fabricated from SMA. Because the form of SMA changes towards temperature, the flexure of the SMA boards in response to being heated by flexible heaters stuck on these boards effects opening anal canal.

Thermosensitive transformer as temperature and output power control device

A temperature and output power control transformer that is applied to an implanted device called artificial sphincter that is composed of shape memory alloy (SMA) is examined. The artificial sphincter is using phase transformation of SMA depending on temperature. To prevent overheating, we examined temperature control utilizing thermosensitive magnetic ferrite. As the temperature rises, the power decreases that is conveyed through the transformer that uses thermosensitive ferrite as its core. If the heater attached to SMA is provided with the electric power through the transformer, it is possible to control the temperature of SMA.

Support Mechanism of a Newly-Designed Mechanical Artificial Myocardium using Shape Memory Alloy Fi bres

As the heart failure is caused by the decrease in the myocardial contraction, the direct mechanical myocardial assistance in response to physiological demand, that is, the synchronous support of the contractile function from outside of the heart, might be effective. The purpose of this study was to develop an artificial myocardium which was capable of supporting the cardiac contraction directly by using the shape memory alloy fibres based on nanotechnology. Some methodologies using novel devices other than the artificial hearts are proposed so far with severe heart disease. However, it was also anticipated that the decrease in cardiac functions owing to the diastolic disability might be caused by using those ‘static’ devices. Then, this study was focused on an artificial myocardium using shape memory alloy fibres with a diameter of 100 – 150 um, and the authors examined its mechanism in a mock circulatory system as well as in animal experiments using goats. Basic characteristics of the material were evaluated prior to the hydrodynamic or hemodynamic examination using a mock ventricular model. The results were as follows: a) The length of the structure was able to be adjusted so that the system could wrap the whole heart effectively. b) In the hydrodynamic study using the mock circulatory system, the myocardial system was able to pump a flow against the afterload of arterial pressure level. c) In the animal experiments, aortic pressure and flow rate were elevated by 7 and 15% respectively by the mechanical assistance of the artificial myocardium, which was driven synchronising with the electrocardiogram, and also, d) The anatomically-identical shape of the artificial myocardium might be more effective for the assistance. In conclusion, it was indicated that this controllable artificial myocardial support system was effective for the mechanical cardiac support for the chronic heart failure.

Preliminary Study on the functional reproduction of an Artificial Myocardium using Covalent Shape Memory Alloy Fibre Based on Control Engineering

The authors have been developing an artificial myocardium using a sophisticated covalent shape memory alloy fibre, which is capable of assisting natural cardiac contraction from the outside of the ventricular wall. We applied engineering method based on robotics control and constructed the artificial myocardial assist system which might be able to regulate derangement and regenerative tensile force on the surface of heart. In this study, a design to surround the total heart has been established in order to refrain from the stress concentration by the mechanical assistance, and the hemodynamic performance of the artificial myocardial assist system were examined in a mock circulatory system as well as on animal experiments using goats. Basic characteristics of the shape memory alloy fibre unit were examined and the displacement control could be achieved under the condition of the different external temperature by feedback using the PID control. And also the increase of the external work of the goats left ventricular pressure-volume relationship were obtained by the assistance using an artificial myocardium with parallel-linked configuration, and therefore it was indicated that the effective ventricular mechanical support could be performed by the device

Development of Transcutaneous Temperature Control System for Implantable Devices

In this work, a small inductor using magnetic property depending on temperature, and transcutaneous temperature control system was proposed. The artificial anal sphincter is actuated by flexible heaters attached to SMA, then opens anal canal. The purpose of this study is to propose the simple system of artificial sphincters controlled its temperature by the inductor consisting of Ni-Cu-Zn based thermosensitive magnetic ferrite. In this paper, a prototype of thermosensitive inductor is designed for evaluations, and tested it to confirm the temperature controllability in order to prevent the SMA from overheating.

Evaluation of heat conductivity of thermosensitive ferrite as temperature dependence device

To realize the temperature control for implanted medical device called artificial anal sphincter utilizing shape memory alloy (SMA) board, a small transformer is made as a control device that consists of thermosensitive ferrite core. Thermosensitive transformer can transmit the electric power to the load heater at the temperature under Curie-point of the thermosensitive ferrite, and can intercept the power at the temperature over Curie-point. Then the power control depending on temperature can be realized. At the device applying only the temperature dependence of magnetic property, a machine trouble rarely happens, so the device can be used safely in a living body. The heat transmission property of the ferrite core was not quite suitable as a thermosensitive device. In this examination, the power loss at the magnetic core is regulated, and the heat transmission property is equivalently improved. Then a long time control of the SMA temperature is confirmed.