ProDigits by
Touch Bionics
Bionic Fingers Give Partly Amputated Hands a Good Grip
December 10, 2009
by
Brendon Nafziger, DOTmed News Associate Editor
While full "bionic" hands have been available for some time, patients with partly amputated hands (missing fingers) tended to have limited prosthetic options. But all that could be about to change.
On Tuesday, Livingston, UK-based developer Touch Bionics announced that ProDigits (short for prosthetic digits) is now commercially available.
Testing on the technology, which offers fully functional electromechanical fingers, began in November 2000. Over the last two years, around 30 people have been outfitted with the device in early clinical applications, including a pianist in London and a former Navy man injured in a plane crash in Washington state.
The ProDigits device is meant primarily for people missing one or more fingers (including the thumb) past the knuckle. Touch Bionics estimates about 40,000 Americans, and 1.2 million people around the world, could potentially benefit from the product.
The bionic appendage slips over the surviving parts of the hand like a glove, the prosthetic digits sheathed in a protective silicone skin. It's battery-powered, with the battery usually housed on a band on the wrist or forearm. (To keep the device slim, the battery has a life of about one or two days.)
Two kinds of sensors
Because each person needing ProDigits has different injuries, the designers of the device ensured that it could work in one of two ways. The first involves electrodes on the skin which pick up the 20 millivolt signal generated when you flex a muscle. "This signal is detected, amplified and sent into the electronics," Hugh Gill, director of technology and manufacturing at Touch Bionics, tells DOTmed News. By reading these electrical impulses, the device allows the user to open and close the bionic digits at will, pinching fingers or closing for a full grip (squeezing up to 22 pounds of pressure, according to Gill).
But not all patients have the right anatomy for the electrodes to be optimal. For them, Touch Bionics came up with a pressure-sensitive pad, which they call the force sensitive resistor. "What happens is if you press on it," says Gill, "the voltage changes in proportion to the amount applied to it. It sends a signal to the hand, so you get proportional control."
The FSR fits on the palm or the surviving part of the finger, snuggling against the skin. Even if, say, the thumb is missing, the pressure from nearby muscles can be used to activate the pad and control the bionics. "If you lost your digits, you can still see skin rocking [if you flex your muscles], and that would be enough to apply pressure to the sensor," says Gill.
Even pointing is possible, thanks to the "stall" mechanism which recognizes when a finger is blocked by an object. For instance, if you press your index finger against an object, and contract the other fingers, the hand "knows" to keep the pointer finger extended. This feature can also be used to intelligently grip objects, such as when giving someone a handshake or picking up the telephone, according to Touch Bionics.
While ProDigits are quite versatile, true individual control of fingers isn't possible. Patients can hunt and peck on the keyboard, for instance, but they can't type, rolling all their digits naturally -- at least, not yet. "Individual discrete control, we're working on it," Gill says.
Learning curve
Gill says the learning curve is from around a couple of weeks to a month. Typically, a patient would first undergo a physical - and emotional - assessment at one of the clinics Touch Bionics works with. (Currently, Touch Bionics has its own North American clinics in Atlanta, Philadelphia, Chicago and Toronto, with operational and test centers in Ohio, and a new clinic under construction in Los Angeles.) If eligible for the device, the patient would have a fully customized hand made for them. (Engineering costs for personalized hands are around 35,000 to 40,000 pounds.) Once outfitted, the patient would practice at home for a few weeks, and then come back for extra tweaking.
Touch Bionics makes sure patients work with an occupational therapist who helps them get the most out of the device. A physician can also use the product's wireless technology to monitor their performance with it, both to better customize the prosthetics, and as research for future versions.
As the hands are fully personalized, patients get to choose their own silicone skins: either colored or clear robotic silicone, or a life-like shell made by LIVINGSKIN, a company just outside New York acquired by Touch Bionics. According to Gill, the LIVINGSKIN studio resembles a Hollywood special effects company, and patients can request the shape and color of their new appendage, and even add freckles, hair or more idiosyncratic cosmetic features, such as bitten nails. "If they bite their nails with their teeth," says Gill, "they want the covering to look like it's been bitten."
Surprisingly, national differences emerge for the skin preferences.
"Americans in general like robotic skins because they've got this device, they want to show it's robotic. They feel comfortable with it," Gill says. "In Europe, most patients want restoration, the human form. I always say, why can't they all feel a bit like my good friends in the States? They can feel comfortable with it, and show it and promote it."