New Sensor-Laden Prosthetic Leg Mimics Natural Gait
Skeletal muscles allow the body to move with grace and subtlety. And yet this is one of the most difficult parts of the body to replicate. Engineers at Vanderbilt University have developed a prosthesis that substitutes the musculature in a human leg with motors, mobilizing the joints and giving amputees a more natural and controlled gait.
On a typical, inert prosthetic leg, the knee works kind of like the stop action on a screen door, allowing the leg to bend while keeping it from buckling. In order to walk, patients have to manipulate the whole assembly with their hip muscles, raising it up and settling it into place. And they expend a lot of energy doing so.
More than difficult, it was arguably dangerous, said Michael Goldfarb, a mechanical engineer at Vanderbilt. Over half of amputees have to think about every step they take. The minute they stop thinking about it is when they fall.
Goldfarb has put together a leg that transfers much of the work from the patient to the knee and ankle joints. "The leg that we developed does have muscles. It does have intelligence," he told InnovationNewsDaily.
Instead of proteins and nerves, Goldfarb used motors, sensors and microcontrollers. They don't have actin-myelin complexes. They use different laws of physics but they do the same thing, he said.
With so much sophisticated machinery on board, controlling the leg becomes complex as well. Fortunately, the prosthetic does most of the work itself, without the wearer even having to think about it. Goldfarb has loaded it with sensors, such as accelerometers and gyroscopes, which follow the movements of both the prosthetic leg and the human wearer. With this information, the system can predict how the patient wants to move and then respond with patterned movements. It can also sense a sudden loss of balance and move to stabilize the wearer after stumbling.
For safety, the user must signal directly to the device before going up and downstairs. But walking requires about as much input as controlling a living limb. You just think walk, Goldfarb said.
However, with the added power come energy concerns. The leg runs on a rechargeable battery that can carry a wearer 14,000 steps or just over 3 miles between charges. In the event the leg runs out of power, it returns to an idle state in which it functions as an inert prosthesis.
Goldfarb does not expect his prosthetic to drive up costs. It keeps costs consistent, but at the same time dramatically enhances the value or the functionality of it, he said.