New prosthetic hands provide fingerprint evidence of radical improvements in the sector
This article was originally published in Clinica
Prosthetic hands remain limited in function, can be heavy and make little or no attempt at looking like the real thing. Now US researchers are working on a prosthesis that looks and feels so real that a cover cosmetic glove is not necessary. It even comes with fingerprints. Karen Riley reports.
Prosthetic hands have changed little in the last half century. Although the devices are shaped like a hand, they have to be covered up by a cosmetic glove. Now researchers at Stanford University Medical School in the US have developed a much more realistic-looking prosthesis.
The new device is also about half the weight of the existing models made by manufacturers Otto Bock and APRL, and it appears to function better, Stanford students Clement Yeh and Rajiv Doshi reported at last week's annual meeting of the Association for the Advancement of Medical Instrumentation in Philadelphia. Current devices activate two or three of the 12 joints in the hand. The Stanford model activates all 12, they said.
The hand is made from solid acrylic. Steel pin joints are placed at three locations - the metacarpophalangeal, proximal and sital interphalangeal within each of four fingers so that they can move realistically. This skeleton is then encased in urethane foam using a mould of the human hand so realistic that it even includes fingerprints.
The thumb is passive but can be placed in several positions for both precise and strong grips. A cable made from Spectra, the strong but light synthetic used in kite flying, is attached to the end of the other fingers to ensure movement. Like existing models the cable is wrapped across both shoulders so that the fingers can move when the user shrugs.
In tests, the prosthesis required 12-24% less force to pick up a variety of everyday objects including a screw, a tennis ball and a soft drink can. The two students estimate the hand will cost $150 - well below the $500 to $800 price-tag of other models.
However, like the gloved models, their hand is not intended for heavy lifting. Those tasks must still be performed by two-hooked prostheses which are preferred by many amputees in the US for their flexibility and strength. But the Stanford model might prove especially popular in Asia and other cultures where the two-hooked prosthesis is frowned upon, Mr Yeh said.
The Palo Alto office of the Department of Veterans Affairs and Hosmer-Dorrance, a company based in Campbell, California, have asked the National Institutes of Health to help finance manufacture of the product.
Researchers at Rutgers University in New Jersey are working on another approach for amputees - a novel controller for multiple finger motion.
The tendon-activated pneumatic (TAP) system, as it is called, was designed to transform natural voluntary movements of tendons in the residual limb into electrical signals using pneumatic foam sensors integrated with prosthetic sockets. The TAP device consists of a polymeric foam connected to a pressure sensor made by SenSym of Sunnyvale, California. Signals produced when the patient moves imaginary fingers were recorded and displayed on a PC. Prosthetic sockets with TAP sensors were placed on three areas on the patient's skin based upon preliminary determinations of finger-related tendon movements.
The device has been tested on three amputees. Following a request for individual finger movements, readings were taken at all three sensor locations to determine the presence or absence of signals and cross-signals. The signals in turn powered a robotic arm. Tests included individual finger tapping and sequential tapping, even playing a simple tune on the piano. The amputees could perform most of the tasks almost immediately and claimed they could feel their phantom finger.
The sensors may be an alternative to myoelectric systems, said Rochel Lieber Abboudi of Rutger's Department of Biomedical Engineering. However, the device will probably only work for below elbow amputees who lost their limb recently - within the last 10 years or so. Its application may be further limited by the fact that the robotic arms currently available are not very portable, she added.