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Biomedicine

Personal Exoskeletons for Paraplegics

A mobile device helps patients with spinal cord injuries walk.

Exoskeletons–wearable, motorized machines that can assist a person’s movements–have largely been confined to movies or military use, but recent advances might soon bring the devices to the homes of people with paralysis.

Assisted Steps: A patient with paralysis stands with the aid of the Berkeley exoskeleton. The exoskeleton moves the patient’s hips and knees to imitate a natural walk.

So far, exoskeletons have been used to augment the strength of soldiers or to help hospitalized stroke patients relearn how to walk. Now researchers at the University of California, Berkeley, have demonstrated an exoskeleton that is portable and lets paraplegics walk in a relatively natural gait with minimal training. That could be an improvement for people with spinal-cord injuries who spend a lot of time in wheelchairs, which can cause sores or bone deterioration.

Existing medical exoskeletons for patients who have lost function in their lower extremities have either not been equipped with power sources or have been designed for tethered use in rehabilitation facilities, to correct and condition a patient’s gait.

In contrast, the Berkeley exoskeleton combines “the freedom of not being tethered with a natural gait,” says Katherine Strausser, PhD candidate and one of the lead researchers of the Berkeley project. Last week at the 2010 ASME Dynamic System and Control Conference in Cambridge, Massachusetts, Strausser presented experimental results from four paraplegics who used the exoskeleton.

Other mobile exoskeletons–like those developed by companies such as Rex Bionics or Cyberdene–don’t try to emulate a natural gait, Strausser says. Because walking is a dynamic motion that is essentially falling forward, Strausser says, many designs opt for a shuffle instead of a natural gait, because “it’s safer and a lot easier.” However, emulating a natural gait mimics the efficiency of natural walking and doesn’t strain the hips, Strausser says.

The Berkeley device, which houses a computer and battery pack, straps onto a user’s back like a backpack and can run six to eight hours on one charge. Pumps drive hydraulic fluid to move the hip and knees at the same time, so that the hip swings through a step as one knee bends. The device plans walking trajectories based on data (about limb angles, knee flexing, and toe clearance) gathered from people’s natural gaits. Pressure sensors in each heel and foot make sure both feet aren’t leaving the ground at the same time.

The Berkeley program was successful. The four paraplegics described in Strausser’s talk, three of whom had been in wheelchairs for years, were able to walk with the device after only two hours of training. “It’s very easy to walk in,” says Strausser. “It moves your leg exactly like you would in your normal gait.” To begin a step, the exoskeleton requires a user to press a button on a remote control; the team is working on a more intuitive interface.

When designing the medical exoskeleton–which uses parts from two military exoskeletons–the team needed controllers and a design that takes into account the user’s lack of strength. While military exoskeletons work with a soldier’s motion to add strength, medical exoskeletons do the opposite, fighting against incorrect gaits or performing the gait, explains Strausser. “The biggest problem is holding a person into the ‘exo’ safely and securely,” she says. After field testing at the University of Virginia’s Clinical Motion Analysis and Motor Performance Laboratory last year, the group developed a proprietary design that keeps users from sliding out of the exoskeleton and distributes the weight of the 80-pound machine. The group plans to make the device lighter and to make a low-cost version that patients can use in their homes. (The research group is affiliated with a company, Berkeley Bionics, that plans to begin selling a form of the technology.)

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“Overall I think it’s a very good device,” says Panagiotis Artemiadis, an MIT researcher who heard Strausser’s talk. He is developing an exoskeleton called the MIT-SkyWalker that helps stroke patients practice walking on a machine that resembles a treadmill. He says he can picture the Berkeley device being used by patients in their homes, particularly if the researchers reduce the weight.

Other mobile exoskeletons to help paralyzed people are just starting to come to market. German company Argo Medical Technologies is releasing its first product, a 100,000-euro exoskeleton intended for use in rehab centers, in October. The company plans to release a home version soon after for about half the price. Unlike the Berkeley exoskeleton, this one, dubbed ReWalk, takes the user a few weeks to learn. “It’s like getting a driver’s license,” says John Frijters, vice president of business development for Argo. ReWalk is customizable, able to tailor the sensitivity of the sensors, step length, and stride depending on how the user feels. It weighs about 45 pounds and runs eight to 10 hours on a charge, according to Frijters.

While ReWalk doesn’t yet have data to share on the advantages of using exoskeletons, “dozens” of patients have tested ReWalk, and “they all enjoy the benefit of being active,” says Frijters. “They have the opportunity to get up from the wheelchair and walk again. It’s very emotional.”

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