Human prosthetics have come a long way in recent decades. We’ve gone from simple plastic molds that vaguely resemble the original limb, to high-tech articulating devices that return most of a person’s mobility. Through all this progress, one nagging issue has continued to plague doctors — there’s still no way for a patient to feel a prosthetic. A new project out of UCLA might be on the path to changing that.
Having something that acts like a leg turns out to be only part of the puzzle, says UCLA grad student Zachary McKinney. When you take a step with your flesh-and-blood leg, the limb is constantly sending sensory signals back to the brain that inform you when it touches the ground, how much weight is on it, and how that weight is distributed among other things. Lacking that kind of feedback in a prosthetic causes long-term problems like uneven gait or strain on the remaining limb.
The UCLA project is not seeking to exactly replicate the sensation of having a real leg, but to provide a system that can relay the same information. The system currently consists of four sensors in the shoe of the prosthetic leg. As the subject takes a step, the system register how much pressure is on each sensor and sends that data to a small computer strapped to the user’s midsection.
The computer will analyze the data, and control the inflation of a series of small balloons on the thigh cuff. These 12 dime-sized silicon balloons are split into four sets of three, each one corresponding to one of the shoe sensors. The more pressure detected, the larger the balloons inflate. Current lag time is roughly 0.1 seconds, which is only a little slower than nerve impulses. For the patient, it is functionally instantaneous.
Results have been encouraging in initial testing. Nine subjects who had lost a leg were asked to walk across a 30-foot wide space with a normal prosthetic. After being given time to acclimate to the pressure-sensitive system, the test was run again. According to the researchers, seven distinct measurements of gait improved with the test rig.