August 6, 2007 The human hand is a magnificent triumph of evolution, combining a complex structure with incredible levels of facility and feedback to enable a stunning range of movements and uses. Its flexibility and usefulness also makes it a debilitating body part to lose and a huge challenge for those involved in the development of bionic limb replacements. The latest innovation from Touch Bionics represents a major step forward in bionic hand development: with four smart motorized fingers and its unique multi-position motorized thumb, all operating from myoelectrically-detected nerve endings in the stump, the iLimb hand opens up a range of grips and fine motor abilities that prosthetic hands have never had before, like using a key in a lock, or one-fingered typing on a keyboard. Another important advance is the simple yet very effective feedback sensors in the fingers which control grip pressure to hold fragile items like styrofoam cups without dropping or crushing them. What's more, patients can choose between the iLimb hand's funky robotic look or another world first - an incredibly realistic skin that you can pull on to make it look almost identical to a real hand.
The iLimb hand from Touch Bionics is the world's first fully articulating and commercially available bionic hand. Featuring five individually powered digits, a multi-position thumb and an optional ultra-realistic cosmetic skin, it represents the start of a new generation in hand bionics.
The iLimb hand is controlled using a traditional two-input myoelectric sensor system that reads nerve impulses from the stump through the skin with no invasive fittings. The control system is exactly the same as that used on existing simple myoelectric prosthetics, so the opening and closing functionality takes only minutes to master.
Grip pressure has been a problem with previous myoelectric hands, and it's an area in which the iLimb excels. The device uses a stall detection system to tell each individual digit when it's exerted enough pressure to grip an object, and stop powering to prevent crushing. “Everyday that I have the hand, it surprises me,” said Sergeant U.S. Army (ret’d.) Juan Arredondo, who lost his hand in Iraq in 2004. “Now I can pick up a Styrofoam cup without crushing it. With my other myoelectric hand, I would really have to concentrate on how much pressure I was putting on the cup. The i-LIMB hand does things naturally. I can just grab the cup like a regular person.”
The individually controlled finger grip system also allows the hand to self-adjust to the shapes of different objects it encounters when closing - a major step-up in facility. “It’s cool how it can adjust to whatever it is grabbing on to,” said lifetime prosthetic user Lindsay Block, of Oklahoma City, OK. “With this new hand, you don’t have to strategize so much about what you do with it because you realize it’s not limited and will adjust depending on what it’s gripping on to.”
Another key step forward is the multi-position thumb, which allows the wearer to manually manipulate the thumb into several different grips to open up an uncharted range of utility. Moving the thumb in towards the palm enables a "power grip" suitable for picking up cans, briefcases and shopping bags with a fully enclosing grip. Moving it out to be more or less parallel with the fingers enables the "key grip" which closes the thumb down on the side of the index finger, letting a wearer turn a key in a lock, or hold a CD or business card. Positioning the thumb to directly meet the point of the index finger enables the "precision grip" to pick up small objects like coins or grapes, or to hold objects while performing fine motor tasks. There's also the ability to close all the fingers but leave the index finger extended to allow natural operation of a keyboard, telephone keypad, ATM cash machine and a range of other daily tasks - and the option to "park" the thumb against the hand to make it easier to put on shirts and jackets without catching.
Finally, there's the cosmetic skins, developed in partnership with ARTech Laboratories and LIVINGSKIN, which mimic a real hand better than any previous articulated prosthetic. Users can choose from a translucent white skin that shows the internal workings of the iLimb hand, or an amazingly realistic high-definition silicone skin that's built to match the skin color and appearance of the user's remaining hand, veins, tendons and all. The realism is astounding, and would fool all but the most eagle-eyed of people in normal day-to-day interactions.
The iLimb hand is powered by a battery that charges overnight and lasts all day, and a very simple one-screw design lets individual fingers be quickly and easily removed for servicing.
It's available now through selected clinics in the USA and UK at a price of around US$18,000, making it between two and three times the price of existing myoelectric devices.
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