<p>In both the military and civilian fields, the traditional tourniquet cannot automatically adjust pressure. If the pressure is too low, the hemostatic effect will not be achieved, and if the pressure is too high, it may cause tissue necrosis. Designing and manufacturing a tourniquet that can automatically adjust the pressure can solve these problems. In this study, we develop a smart tourniquet capable of producing a controllable pressure of more than 30kPa for circumferential applications such as for mechanical counterpressure (MCP) suits or medical life-saving tourniquets to stop the outflow of blood. This smart tourniquet is 40 mm wide, and at least long enough to meet 99th percentile leg size at the maximum circumference. The designed tourniquet utilizes NiTi Shape Memory Alloy (SMA) coils to provide the required actuation force and pressure. SMAs enable generating high forces and having large displacements when stimulated. Also, they have been proven to be safe and feasible choices for wearable devices. In this study, the SMA actuators are first electro-thermal-mechanically characterized and the voltage-force-displacement relationships are obtained. Then, to accurately adjust the pressure applied on the body, a closed-loop controller is implemented while an analog air pressure sensor and pressure cuff measure pressure and provide feedback for the system. To control the system, a Proportional Integral Derivative (PID) controller is implemented. To do so, the system dynamic equations are represented. Then the PID gains are adjusted to achieve the required pressure level, stability, and settling time. The thermal activation of SMA coils is achieved through Joule heating, and a microcontroller and a programmable power supply are used to provide the input signal. To our knowledge, this is the first demonstration of accurately closed-loop controlling an SMA-incorporated compression technology. This paper enables new, dynamic systems with controllable activation and low effort donning and doffing, with applications ranging from healthcare solutions to advanced spacesuit design.</p>

A Smart Controllable Sma-Based Tourniquet

Paper Proceedings: https://asmedigitalcollection.asme.org/SMASIS/SMASIS2021/volume/85499

ASME 2021 Smart Materials, Adaptive Structures and Intelligent Systems (SMASIS2021)

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