The thing that separates us apes from monkeys is the range of motion of our shoulders. Able to swoop from vine to vine, apes have a very complex joint whose motion hasn’t been studied in full detail. That’s because it is very difficult to position sensors on and around the shoulder that will conform to the shoulder and stay in place as it is exercised. When one’s shoulders are injured, the typical way of measuring recovery is with a simple protractor that simply indicates how many degrees of movement the arm can achieve.
Researchers at the University of Michigan have now developed an unusual device that can facilitate objective shoulder joint assessments.
Printed as a flat object, the device takes on a 3D structure as it is pulled apart into its working shape. This trick is possible thanks to methods taken from the Japanese art of kirigami, which involves making sculptures from cut and bent paper.
It is made of plastic arranged in concentric circles, and when pulled looks like a Slinky toy. The circles can hug the shoulder, with the wider ones wrapping around the more distant part of the shoulder.
Strain sensors on the plastic material allow for measurements of motion in different directions and paths. Currently there are only two in the Michigan team’s prototype, but it should be possible to integrate many more using the same techniques.
This device has already been tested against a video based joint tracker, the kind used in movies, and it was shown to have an impressive correlation. The researchers hope that rehab clinics will be able to take advantage of their technology to guide therapy and help patients recover quicker.
Here’s a short video report from the University of Michigan about the research:
Study in Advanced Materials Technologies: Developable Rotationally Symmetric Kirigami‐Based Structures as Sensor Platforms