Researchers from North Carolina State University reported on testing of a lightweight, soft textile-based sensor prototype patch made up of a lattice of conductive yarns that can measure pressure within a prosthesis. They tested the system on a prosthetic limb and in walking experiments with two human volunteers, finding the system could reliably track pressure changes in real time.
“What people commonly use to measure pressure within prosthetics are rigid sensors,” said Jordan Tabor, the study’s first author and a graduate student in the university’s College of Textiles. “They’re hard, they’re bulky, they can be heavy. These are not things that amputees can use on a daily basis because rigid sensors negatively affect the fit of amputees’ prosthetics. Rigid sensors can also cause discomfort. We designed sensors that can be integrated into textiles in a way that doesn’t cause any additional discomfort for the user and could be worn on a more regular basis.”
In one experiment, the researchers tested whether the patch could detect changes in pressure when they placed it on an artificial limb, turned at different angles. Then they used it to test pressure changes when an able-bodied person wore the sensor patch while walking with a bent-knee adaptor and while shifting their weight between legs.
In their last experiment, a volunteer with a transtibial amputation wore the patch on the liner of their prosthesis in areas where it typically applies higher pressure. The researchers tested the sensor patch while the volunteer shifted weight and walked on a treadmill.
“This approach that we thought of a few years ago does work, and it’s a readily manufacturable technology,” said Tushar Ghosh, PhD, the study’s co-corresponding author. “You cannot put materials next to the skin that are uncomfortable and may not be safe. So we are putting things that are used around us all the time and are soft and flexible.”
The work was a collaboration between researchers in textile, electrical, computer and biomedical engineering at NC State. The human experiments were performed by rehabilitation engineering researchers led by Helen Huang, PhD, in the University of North Carolina/NC State Joint Department of Biomedical Engineering and a senior co-author of the paper.
The research team created the sensor patch by sewing the yarns together in such a way that they created an electromagnetic field. When the researchers sewed the yarns into a lattice and applied a small amount of electrical power using a small battery, they found they could measure the amount of electrical charge drawing the yarns together at each lattice point. The charges changed depending on how close the yarns were together, which related to how much pressure was applied by the wearer.
“We connected the textile fibers to an electrical circuit that is a little larger than a quarter, and that can scan as many as 10 by 10 fibers,” said the study’s co-corresponding author Alper Bozkurt, PhD, a professor of electrical engineering at NC State. “That gives us 100 points of measurement. Everything is connected to a tiny microcomputer, which has a radio for wireless data tracking.”
While the researchers used a yarn that was commercially available for the study, they are also working on developing their own textile fiber to detect more than just pressure changes in the prosthetic socket.
“Our broader vision is to design something like a sock, or to integrate the sensor system into the prosthetic socket, so when a person dons their prosthesis, they are able to monitor what’s happening in terms of pressure distribution and other measurements,” Huang said.
The study, “Textile-based Pressure Sensors for Monitoring Prosthetic-Socket Interfaces,” was published online in IEEE Sensors Journal.
Editor’s note: This story was adapted from materials provided by North Carolina State University.
