Soft sensor could map pressure points for amputees

Published in IEEE Sensors Journal, the team’s study explored how their prototype patch, which incorporates a lattice of electrically conducive yarns and connects to a computer, could help to detect pressure points in the socket of an amputee’s prosthetic limb. 

The team comprised researchers in textiles, electrical, computer and biomedical engineering at NC State. The study’s first author Jordan Tablor, a graduate student in the NC State College of Textiles, explained that rigid sensors are commonly used to measure pressure within prosthetics.

“They’re hard, they’re bulky, they can be heavy,” Tablor said in a statement. “These are not things that amputees can use on a daily basis because rigid sensors affect the fit of the amputees’ prosthetics.” He added that they can also cause discomfort, prompting the team to design a sensor that could be integrated and used more regularly without causing further discomfort to the user.

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Researchers said their first experiment involved testing whether the patch could detect changes in pressure when placed on an artificial limb turned at different angles. They then tested 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.

Next, a volunteer with an amputated lower leg wore the patch on the liner of their prosthetic limb in areas where it typically applies higher pressure. They tested the sensor patch while the volunteer shifted weight and walked on a treadmill, finding the system was durable and could reliably monitor pressure changes in the socket.

Part of their work involved designing the system to be lightweight and small enough for human use. According to the team, they created the sensor patch by sewing the yarns together in such a way that they created an electromagnetic field and applied a small amount of electrical power using a small battery. They found that they could measure the amount of electrical charge drawing the yarns together at each lattice point.

The charges change depending on how close the yarns are together, which is related to how much pressure is applied by the wearer. They connected yarns, insulated them, laid them on a textile fabric and connected them to a small electronic device to capture the data. A small radio was also included to wirelessly track measurements.

“We connected the textile fibres to an electrical circuit that is a little larger than a quarter, and that can scan as many as ten by ten fibres,” said co-corresponding author Alper Bozkurt, an electrical engineering professor at NC State. “That gives us 100 points of measurement.”

Researchers said they are now working on developing their own textile fibre to detect more than just pressure changes in the prosthetic limb socket. Their next step is to integrate the sensors into prosthetic sockets directly, or into a wearable item.