Upgrading the Prosthetic Hand

A lightweight prosthetic hand uses hydraulics to achieve more natural finger movement.

A lightweight hydraulic hand with individually powered fingers could change the lives of amputees, say researchers in Germany. The Fluidhand, according to its developers, is lighter, behaves more naturally, and has greater flexibility than artificial hands that use motorized fingers.

Freedom to move: The Fluidhand (above) uses lightweight miniature hydraulics to enable the wearer to move each finger individually. Credit: The Research Center, Karlsrühe/Forschungszentrum

The Fluidhand prototype, developed by a team led by Stefan Schulz at the Research Center in Karlsrühe, in partnership with the Orthopedic University Hospital, in Heidelberg, Germany, has flexible drives located in each of its finger joints, enabling the wearer to move each finger independently. Lightweight miniature hydraulics are connected to elastic chambers that can flex the joints of the fingers. As sensors on the fingers and palm close around objects, nerves in the amputation stump pick up muscular sensations so that the amputee can use a weaker or stronger grip. The prosthetic provides five different strengths of grip.

"It is so intuitive that learning to use the device only takes about 15 minutes," says Schulz.

Last September, 18-year-old Sören Wolf, who was born with only one hand, became the first person to use the Fluidhand. According to German press reports, Wolf was able to type on a keyboard with both of his hands for the first time in his life, and he told reporters that, when he's wearing the Fluidhand, he doesn't feel handicapped anymore.

International interest in the Fluidhand peaked late last month, when it was announced that the Orthopedic University Hospital is testing the device in comparison with the i-LIMB Hand. Wolf is the first amputee to use both prosthetics.

Produced by the Scottish company Touch Bionics, i-LIMB was the first prosthetic hand that enabled the movement of individual fingers. The prosthetic, released last summer, uses a different technical principle than the Fluidhand. With i-LIMB, movement is enabled by five small, battery-powered motors that are embedded in each finger. Schulz believes that the hydraulic system has some advantages over the motorized fingers. "In contrast to the movement with electric motors and transmissions, the Fluidhand remains soft and flexible," he says. "Articles can therefore be seized more reliably, and the hand feels more natural."

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Both devices are significant improvements over conventional hand prostheses that only enable the wearer to pinch the thumb and forefinger to create a grip.

"There are many hand movements that require individual digit movements," says Hugh Herr, director of the Biomechatronics Group at the MIT Media Lab. "The development of individual finger movements in a prosthetic is a remarkable step forward."