This Bionic Ankle Walks Like It's Alive

The human lower leg is a marvel of biological engineering -- it lets you have a long, strong stride while minimising exertion and joint strain. But conventional spring and hydraulically-driven prosthesis worn by amputees offer no such benefit and can cause osteoarthritis-inducing skeletal strains. The BiOM T2 system aims to rectify that.

The last time we discussed the BiOM company, it was still calling itself iWalk, and had just begun rolling out the T2 system. Today, more than 900 such devices have been distributed with nearly half being employed by US veterans.

The T2 system essentially replaces the function of its wearer's lost calf and tendon, providing more energy than it stores. See, when you stride, your trailing leg calf and achilles tendon flex, propelling you forward. Since this requires more energy than what is absorbed during the stride, it can't be accurately replicated by a passive system of springs and hydraulics.

The T2 however, employs a pair of microprocessors and six environmental sensors to adjust the bionic ankle stiffness, contraction power, position and damping thousands of times each stride. It stiffens the ankle at heel strike to dampen the shock, then softens and flexes the joint to propel the user forward in an easier gait. The system can adapt nearly instantly to changing terrain and walking cadence and is programmed to match the wearer's walk during its initial fitting, or "Personal Bionic Tuning" as the company calls it.

Still, the benefits come hard and fast once the users get used to the system. The system is much easier to adapt to than conventional peg legs. "Often, within minutes, a patient is walking around, even running around," Hugh Herr, an Associate Professor of Media Arts and Sciences at Massachusetts Institute of Technology (MIT) and BiOM's CTO, said in a press release. Other models can take weeks or even months to get used to. And since the T2 delivers a more natural gait than passive prostheses, stress on the rest of the leg and lower back is reduced, which potentially can slow or delay the onset of osteoarthritis, endemic among ageing amputees. [BiOM via R&D Mag]