BEIJING, Aug. 30 (Xinhuanet) -- Conventional bionic arms make use of batteries and electric motors, but research reveals rockets can help power robotic arms leading to the development of "better, stronger, faster" bionic limbs.

A new prototype rocket-powered mechanical arm can lift about 20 to 25 pounds ─ three to four times more than current commercial prosthetic arms ─ and can do so three to four times faster.

"Our design does not have superhuman strength or capability, but it is closer in terms of function and power to a human arm than any previous prosthetic device that is self-powered and weighs about the same as a natural arm," said researcher Michael Goldfarb, a roboticist at Vanderbilt University in Nashville. "It has about 10 times as much power as other [robotic] arms."

The rocket-powered arm also has greater freedom of movement and dexterity than any other prosthetic in use today. Conventional prosthetic arms have only two joints, at the elbow and the "claw." This prototype functions more naturally than previous models, with a wrist that can twist and bend, and fingers that open and close independently.

"Battery power has been adequate for the current generation of prosthetic arms because their functionality is so limited that people don't use them much," Goldfarb said. "The more functional the prosthesis, the more the person will use it and the more energy it will consume."

The weight of the batteries needed to power a bionic arm for a reasonable amount of time is a problem. This led Goldfarb and his colleagues to look for alternatives ─ in this case, rockets.

The radical design is similar to rocket systems that help the space shuttle and satellites maneuver in orbit.

It uses a miniature rocket about the size of a pencil that burns pressurized liquid hydrogen peroxide using iridium-coated alumina granules as catalysts. It generates pure steam that forces pistons up and down, producing motion. Steam gets vented out through a porous skin-like cover, where it evaporates like normal sweat.

A key concern was protecting the arm's owner and those in close proximity from heat the arm generated ─ the steam can get up to 450 degrees Fahrenheit (232 degrees Celsius). The hottest parts are covered with special insulating plastic, making them safe to touch. A small sealed canister of hydrogen peroxide that fits easily in the upper arm can provide enough energy to power the device for 18 hours of normal activity.

The research has been funded by the Defense Advanced Research Projects Agency in the United States, which aims to develop better prosthetic limbs. Improvements in body armor and battlefield medicine have reduced the number of casualties from conflicts, but the side effect is a significantly increasing number of amputees, as has become evident among veterans of the ongoing war with Iraq.

(Agencies)