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Smart Sock Adds Sensations to Prosthetic Leg

A prototype of a smart sock that can add sensation to a lower-limb prosthesis was presented at the Association for Computing Machinery’s (ACM’s) User Interface Software and Technology Symposium conference held October 16-19, where it was selected as one of the best papers. The device was developed by a team of researchers from the University of Applied Sciences Upper Austria, Linz and Hagenberg campuses.

Customization allows for mapping custom regions dynamically to actuators via a mobile app (left, middle). The knee guard detects the degree of bending of a knee-joint (right). Photograph courtesy of ACM Digital Library.

The smart textile prosthetic sock, called the proCover, is made of layers of conductive fabric that sandwich a piezoresistive layer, creating a pressure-sensitive grid that covers the foot and ankle of the prosthesis. It is then connected to a ring of motors that vibrate at different frequencies depending upon the pressure on the foot. The motors can be attached to different bands and worn on the upper arm or thigh.

Rather than sensor technologies being designed to be directly embedded into future prostheses, the proCover offers “a noninvasive, self-applicable, and customizable approach for the sensory augmentation of present-day and future low- to mid-range priced lower-limb prosthetics,” according to the authors of the paper, which is published in the ACM Digital Library. . The researchers intend the smart sock technology to provide an option to people for whom other prosthetic options are out of reach due to cost, accessibility, health status, and personal attitudes towards elective surgery.

With a cohort of eight participants with lower-limb amputations, the research team investigated the implications and potential of having pressure sensing on all surfaces of the foot, the acceptability of a textile form factor for a sensing solution, customization and personalization in the context of sensing for prosthetics, and possible factors that influence users’ sensing needs. A pilot study to test the smart sock was conducted with four of the original participants, who each used a different type of prosthetic leg. Two of the participants had transfemoral amputations, one had a transtibial amputation, and one had bilateral transtibial amputations. Tasks included touch-position discrimination and applying pressure to a car pedal. The researchers also fabricated and tested a sensing knee guard device on the two participants with transfemoral amputations to test knee-bend detection.

According to the pilot study results, the sensing socks dynamically created and mapped sensing regions to actuators, enabling participants to distinguish between touches on different locations and at different levels of applied pressure, while the knee guard demonstrated the potential for the same fabric approach to be used for bend-detection for prosthetic limbs.

For information about complementary research that was conducted by several members of this team, read “Patient Fitted With Prosthetic Leg That Can Feel.”