A System Utilizing Metal Hydride Actuators to Achieve Passive Motion of Toe Joints for Prevention of Pressure Ulcers: A Pilot Study

This paper describes the influence of human toe movement on blood flow and the design of a toe joint passive motion system for preventing pressure ulcers. First, we measured lower extremity blood flow in the foot during active and passive motion of the toe to facilitate the design of new rehabilitation equipment. Also, the flexion and extension angles and the force of the toe joints were measured to determine appropriate specifications for the system. Increases in blood flow were observed at the external malleolus during movement. Flexion and extension angles and the force of the toe joints were found to differ significantly among participants. It is shown that a toe joint passive motion system can be effective in preventing pressure ulcers. On the basis of these results, a device using alloys of metal hydride (MH) as an actuator that is suitable for the system to initiate toe motion, was developed. 1. Introduction Inactivity due to bed rest during convalescence from illness can lead to the development of pressure ulcers. A pressure ulcer is defined as a lesion that is mainly caused by pressure in combination with shear stress. Recent studies indicate that excessive tissue/cell deformation, ischemia, and ischemia-reperfusion due to prolonged loading are important factors in pressure ulcer development [1, 2]. Thus, dispersion of external forces, shortening ischemic period, and increased blood flow at common sites play important roles in the primary prevention or symptomatic improvement of pressure ulcers. Many researchers have reported on the use of force dispersion to prevent pressure ulcers [3, 4]. Some researchers have developed cushions or mattresses with internal pressure that is controlled by water or air [5, 6], and the thickness, shape, and composition of these cushions have been discussed by other researchers [7–9]. Meanwhile, mechanical stimuli may also be effective in pressure ulcer prevention from microcirculatory point of view [10]. It has been reported that active motion of the human toe or oscillating the lower extremity in an appropriate cycle can increase skin blood flow of the foot [11, 12]. On the basis of these findings, it is expected that toe exercise will have some effect in preventing lower extremity pressure ulcers. However, aggressive exercises for pressure ulcer prevention are difficult to implement when the patient must maintain bed rest. Thus, a preventive exercise or motion system that can be used in a face-up/down position is required. It is essential for such a system to be simple to use and reliably safe for patients and