Smart Socket Prostheses
An Office of Naval Research and UC San Diego Center for Healthy Aging funded project.
Project title: Monitoring Socket Prosthesis Interfaces using Distributed Pressure Fabric Sensors
Source of support: Office of Naval Research and Center for Healthy Aging, UC San Diego
Hundreds of thousands of people, including military personnel, undergo limb amputations each year, which is are primarily caused by either traumatic injury or peripheral vascular disease. Amputees can be fitted with socket prostheses to help them regain functionality and resume physical activity. Despite the socket being customized, lower-limb amputees still suffer from complications and discomfort while often developing painful, difficult and expensive to treat, and sometimes life-threatening pressure ulcers that can potentially lead to re-amputation, among other serious complications. It should be noted that the issue of pressure ulcers extends far beyond amputees to include patients with spinal cord injuries, bound to a wheelchair, or immobilized in general. Therefore, the objective of this study is to monitor pressure distributions using fabric sensors lined along the interior surface of socket prostheses. The system utilizes strain-sensitive nanocomposites coupled with an electrical impedance tomography (EIT) conductivity distribution reconstruction technique. First, carbon nanotube (CNT)-based thin film strain sensors were integrated with flexible and waterproof textiles (Fig. 1). These piezoresistive nanocomposite sensors, unlike conventional transducers, are unique in that every location of the material is sensitive to strain (or pressure). Second, a near-real-time EIT algorithm was implemented. One can then use EIT to map the 2D spatial conductivity distribution (or resistivity) of the film (which is pre-calibrated to pressure) to achieve distributed pressure monitoring. Fig. 2 shows a representative EIT result, where the fabric sensor successfully detected an applied pressure point (Fig. 1) at the top-left corner of the fabric. Distributed pressure monitoring was also validated on nonplanar and complex surfaces, such as at the base of a next-generation socket prosthesis (Fig. 3).
Dr. Alison Moore, UC San Diego
Prof. Sheng Xu, UC San Diego
L. Wang, S. Gupta, K. J. Loh, and H. S. Koo, 2016, "Distributed Pressure Sensing using Carbon Nanotube Fabrics," IEEE Sensors (1530-437X), IEEE, 16(12): 4663-4664. DOI: 10.1109/JSEN.2016.2553045
Fig. 1. A nanocomposite fabric sensor is subjected to distributed pressure sensing tests in the laboratory.
Fig. 2. The electrical impedance tomography algorithm outputs the spatial conductivity maps of the fabric sensor, and localized changes in electrical properties correspond to the severity and location of applied pressure.
Fig. 3: Validation of distributed pressure sensing on the socket base