‘Smart’ leg to keep people walking

The US Department of Energy’s Sandia National Laboratories is involved in a collaboration with the Russian nuclear weapons laboratory, Chelyabinsk 70, to develop ‘smart’ legs – entire smart lower limbs – to replace those amputated annually from thousands of Americans.

Sandia National Laboratories will develop sensors and chips for the ‘smart’ legs, whilst materials work and testing will be carried out by the Russian team. ‘This is about making a leg that is more like a missing limb than a collection of components ever can be,’ said Diane Hurtado of the Smart Integrated Lower Limb (SILL) project team. ‘This limb will have a digital control system to make it smart.’

The leg is intended to simulate the human gait whether on uphill, downhill, or rugged terrain.

To do so, a microprocessor-controlled module implanted in the leg will respond to sensor input from multiple sources. The microprocessor will control hydraulic joints and piezoelectric motors that power the ankle, knee and socket.

The leg socket will, say researchers, adjust to the changing diameter of an amputated stump over the course of a day, which is anticipated to reduce sores, improve comfort, and increase the amount of time the leg can be used. Sandia researcher Dave Kozlowski, who has designed robotic architectures for surgical operating rooms, said: ‘The majority of lower-limb prosthetic devices are based upon passive technologies that require far more energy for amputees to cover the same distance as non-amputees.’

In passive technologies, as the thigh moves forward, inertia opens the knee joint, the artificial shin swings forward, and, when the entire structure locks, the wearer can pass his or her weight over it. The feet are usually not ‘smart’ in adjusting to terrain.

‘We intend to develop a much more efficient device, with sensors placed at strategic points along foot and leg, that will enable a more normal and efficient walking gait,’ said Kozlowski. A proper limb motion will return energy to the wearer instead of draining it, he added.

Sandia researchers are also facing the challenge of developing a power source light enough for an amputee to feel comfortable carrying it, said Kozlowski.

Sandia anticipate producing a marketable ‘smart’ leg by 2002.