Researchers in the Intelligent Systems, Robotics, and Cybernetics group at Sandia National Laboratories (Sandia), Albuquerque, New Mexico, have developed a sensor that will monitor volume changes in the residual limbs of prostheses users and automatically accommodate for those changes. The researchers developed a three-axis pressure sensor, about the size of a quarter, to monitor fit and detect deviations. The sensors fit inside an elastomer prosthetic liner similar in thickness to a gel liner. Sandia has filed a patent application and has presented papers at conferences about the work.
Jason Wheeler demonstrates a liner aimed at helping prosthetic limbs fit better. Photograph by Randy Montoya courtesy of Sandia National Laboratories.
Jason Wheeler, PhD, who has been studying prosthetics at Sandia for ten years, says the sensor is unique because it detects pressure in three different directions: normal pressure, and horizontal and vertical shear forces, which can cause rubbing, blisters, and abrasions. Sensors can be placed in various spots, measuring three directions at each site. Other designs have placed pressure sensors in sockets, but they measured only normal pressure, said Wheeler. “This extra information gives you better ability to know when you need to make modifications because the shear pressures tend to be a little more sensitive to changes in socket shape than normal pressures,” he added.
The system automatically adjusts socket shape by moving fluid into bladders inside the liner. The bladders are filled using valves and pressurized liquid on the outside of the liner and add volume only where it’s needed.
“Being able to put additional fluid volume locally, where you lost it, is an important component,” Wheeler said. Prototypes have been developed to fill and empty the bladders automatically, but he says more research is needed to determine when it’s best to add and remove fluid.
A liner can accommodate sensors and/or bladders. “Sometimes you might just want to sense, sometimes you might just want to fill a bladder, sometimes you might want to do both, so the system is flexible enough you can create a liner that does any of those functions,” Wheeler said.
Development is continuing and more testing with subjects with amputations is needed, but the technology “is getting mature enough where before too long, if we want it to be successful, we’re going to have to hand it off to a commercial entity to market it,” Wheeler said.
Editor’s note: This story was adapted from materials provided by Sandia National Laboratories.