A researcher from the University of Michigan (UMich) has developed a wearable sensor patch to measure the range of motion of hard-to-assess areas of the body using principles from the Japanese paper art of kirigami.
When Max Shtein, a professor of materials sciensssssssce and engineering at the University of Michigan crashed his bicycle and broke his collarbone, he was dismayed to find that his physical therapist assessed the range of motion in his shoulder with a basic protractor. The method is prone to large errors, and he had no way of repeating the measurements at home.
So, he teamed up with Ph.D. student Erin Evke to design a new sensor patch that can contour to the shape of the body. The patch uses electronic sensors to understand the functional range of motion as opposed to today’s static measurements. Influenced by kirigami, the Japanese art of creating 3D structures from cut paper, the sensor can hug the curves of a joint and yet can be manufactured flat, reports UMich.
“The shoulder in particular moves in a very complex way. It’s one of the most well-articulated joints in the body,” said Prof. Shtein.
“Nobody’s really been able to track it properly with anything wearable, and yet it’s key to so many activities in sports and daily life.”
To make the patch, Evke laser cut a thin sheet of plastic into a labyrinth of concentric ovals. The shape pulls apart almost like a Slinky, and the cuts open into a lacework over the shoulder.
“If you take a sheet of paper and try to wrap it around a sphere, it’s impossible to do so without folding or wrinkling the paper. This would significantly stress the sensors before your measurement even began,” Evke said. “Our cut pattern avoids this problem.”
Because these structures transform from a flat sheet to a wrinkle-free, 3D shape, they can be manufactured with existing, cost-effective technologies. Shtein estimates that the cost of individual sensors could be below $10, assuming mass production.
The team envisions that this kind of inexpensive sensor could be given to physical therapy patients, enabling them to log exercises and see progress through a smartphone app. This could help keep patients honest about doing their exercises and also provide more detailed information to therapists about each patient’s progress.
The study is published in the journal Advanced Materials Technologies.