Enabling Bionic Limbs

Advances in modern technology are clearly visible when you begin to think that science fiction resembles present day medical advancements. Prosthetics are delivering life-changing assistance to those that have lost limbs - providing the ability to perform typical daily tasks that most people take for granted.

Biomechatronics studies the integration of mechanics, electronics and biology. Limb functioning is due in part to three major components: biosensors - nerve cells and muscle cells; controllers - the brain and nerve signaling; and actuators - the muscles moving the limbs. Prosthetics based on biomechantronics require the same components. Mechanical biosensors that are placed on the skin, or electrodes that are implanted into muscles, detect electrical activity; this is also known as myoelectric technology. Once the activity is detected, the information is sent to the controller, which interprets the signal that is then relayed to the actuator. Finally, the actuator is what controls the actual prosthetic - be it movement and/or force.

So, with the technology known on how to create prosthetics peopler are able to return to their daily tasks, with little to no impediment.

YEARS OF DEVELOPMENT

Touch Bionics, developer of the i-LIMB Hand prosthesis, began in 1963. A research program led by David Gow at Edinburgh's Princess Margaret Rose Hospital in Scotland, started as a way to help children affected by Thalidomide - a drug first marketed in Europe in the late 1950s as a treatment for morning sickness, which resulted in the birth of thousands of children with stunted or missing limbs. Gow created a fixed gearbox, small enough to fit in the knuckle of each finger, delivering the ability to have five working fingers. "It was the first hand to come to the market that actually has articulating fingers, just like your own hand," Gow says.

According to Phil Newman, director of marketing with Touch Bionics, "We were originally a technology research lab that in earnest started the R&D program in the 1990s within the Scottish National Health System (NHS). Then we became the first company to spin off from the Scottish NHS, taking the core intellectual property (IP), the invention, to commercialization."

Each individually-powered finger is driven through a small DC motor and worm-and-wheel gear arrangement.

That key IP acquired through the spin-off was the concept of the finger rotating around the gearbox, which is really the underlying technology that exists within the i-LIMB Hand today. With that technology, the fact that the need for prosthetics is not always an entire limb, but sometimes just a finger, the company researched early fittings of ProDigits - short for Prosthetic Digits - which are self-contained fingers that are individually-powered and controlled.

FULL ARTICULATION

Each finger of the i-LIMB Hand has a cylindrical motor located within the first main bone of the finger. It is the finger that rotates itself around a fixed gearbox located where the knuckles reside in the i-LIMB Hand; the thumb has a similar structure as well. "Basically, what you have are five digits that are independently-powered and they move separately, but they are all controlled from one signal - myoelectric technology," Newman explains. "We are using existing and traditional myoelectric input signals in our device."

Imagine someone lost their midforearm, which is called a trans-radial injury. There is residual muscle in that stump, so that stump is put into a socket that is in the shape of a forearm. Within that socket there are two electrodes - one on the top and one on the bottom of the forearm - and those electrodes are essentially providing an on/off signal to the i-LIMB Hand. So, an open signal is sent from the top muscle and a close signal is sent from the bottom muscle.

"The patient is providing, what I would call, a glorified open and close signal to the hand, and the hand is actually opening and closing according to the patient's signals," Newman states. "The myoelectrically-controlled hand is driving electrical motors, which in turn allows the individual fingers to respond through sensors in the motors, so the fingers know to stop powering once the required level of resistance to safely pick up an object has been achieved."

The myoelectrically-controlled hand is driving electrical motors, which in turn allows the individual fingers to respond through sensors in the motors.

For example, picking up a wine glass, something fragile, or another object that has different shapes and contours to it, responds quicker with feedback from the motors of the finger, and this is where you see the advantage of the individual finger controls.

Software provides speed and gripstrength control to the device while the actual grip is supported by a grip surface called cosmesis - a skin covering over the entire prosthetic.

STRUCTURAL MAKE-UP

DuPont Zytel is the product that is the actual structure of the prosthetic - the skeletal structure of the i-LIMB Hand. Zytel is a light-weight, longfiber plastic that is injection-molded, which results in a strong and robust prosthetic housing. Within the skeletal structure of the i-LIMB Hand are the necessary components: cylindrical motors, fixed gearboxes, controller board and software. The batteries that provide power to the hand are normally located in the forearm prosthesis.

Sergeant U.S. Army, retired, Juan Arredondo, who lost his hand in Iraq, uses the i-LIMB Hand and states that ‘The i-LIMB Hand does things naturally.'

The prosthetic must also be protected from moisture and dust, so two options are available to users. i-LIMB Skin is a semi-transparent product that wraps over the exact contours of the hand while still holding and showing the "robotic" nature of the hand - not offering a lifelike skin coloring. Then there are other cases where the individuals desire to have the most lifelike prosthetic as possible, wanting to look aesthetically correct. For these users there are Living Skin products, a high-definition cosmesis available in ten colors specifically-designed to work exactly with the i-LIMB Hand.

MORE TO COME

Touch Bionics' i-LIMB Hand is currently involved in a prosthetics trial conducted by researchers in Sweden. The protocol for the trial is based on a combination of new and existing users, and likewise bilateral users who have had no prosthesis or a previous-generation prosthesis. Researchers are looking at upper limb occupational therapy, such as: can they perform dexterous tasks; can they perform heavy-duty tasks; can they perform tasks about head height from a functional perspective; and from the psychological perspective; are they happy with their prosthesis?

When repair of a ProDigit is required, removal of one screw is all it takes.

All of these areas were tested in a controlled environment that was completely independent of Touch Bionics - they merely provided ten i-LIMB Hands for the study that concluded this past October. As they eagerly await the results, which will be published in early 2009, Newman already has some knowledge of what users want: "In Europe, particularly, we find that people want to blend back into society rather than show their robotic-like hands. Additionally though, we are interested in learning about the ability for people to get back to a high level of functioning."

"What i-LIMB delivers are individual fingers and the rotation of a thumb in a prosthetic that looks and functions as the patient desires. Those are really the key developments and innovations that have never before been open to patients in the past," Newman concludes.