Touch Bionics is moving forward with its prosthetic fingers. They have much of the same capability as the i-Limb, but customized to each amputee's unique physiology.

In the world of prosthetics, there’s really no such thing as “one size fits all.” Back when we discussed the i-Limb from Touch Bionics, we mentioned that the Scottish company’s next big development would be bionic fingers. Well they’ve arrived. Pro-Digits are powered mechanical fingers which can be controlled by measuring electric signals from nerves using pads on the skin. Touch Bionics has fitted more than thirty patients with Pro-Digits devices, each uniquely built to correspond to differing levels of amputation. As with the i-Limb, the bionic fingers can detect objects as they close to prevent crushing something delicate and can be installed in different grips to help with tasks such as typing. Check out the Pro-Digits in action in the video below.

There’s been a ton of really exciting news about prosthetics this year. Besides i-Limb, we’ve seen artificial hands and arms from Deka, DARPA’s Prosthetics Revolution Program, and Smart Hand. Artificial intelligence in lower limb prostheses is also advancing at a wonderful pace. While each device has its own merits, Touch Bionics has geared i-Limb and Pro-Digits to be market ready and user friendly as soon as possible. There are already more than 600 users of i-Limb and it looks like Touch Bionics is trying to get Pro-Digits to enjoy the same popularity.

Typically a mechanized prosthesis can handle one kind of input: pressure sensitive pads, electrical signals measured from the skin, or wires directly connected to nerves. Pro-Digits can be adapted to handle either of the first two inputs and Touch Bionics plans on eventually designing products that can handle the third. Myo-electric sensors measure nerve impulses through the skin. Basically, an amputee’s nervous system will still send commands to the missing limb and these sensors can detect those commands and use them to direct the artificial fingers.

As each prosthesis is different, and each patient has a different amputation, getting Pro-Digits to respond to myo-electric control can take some calibration. New patients shouldn’t expect to have the level of control demonstrated in the video right away. Touch Bionics does have software guided feedback to help train new users, and information is routed from the limb using Bluetooth. It would be awesome (and completely unlikely) to have Pro-Digits adapted to serve as a headset for a phone.

One of the really remarkable features of Pro-Digits is that they can be cosmetically matched to the rest of your body. Using a life-like surface (called “LivingSkin”) Touch Bionics will shape a prosthesis so that it can closely resemble a natural hand. Don’t believe it could pass in public? The pictures of customized i-Limb hands will change your mind.

It took me a few seconds to recognize the i-Limb on the right.

I guess the i-Limb is the one on top?

Touch Bionics estimates that there are 52,000 Europeans who may be a match for Pro-Digits, and more than 1.2 million such individuals worldwide. That’s a lot of bionic fingers to be made. Each prosthesis is likely to have a different price tag (depending on the exact form it takes) but the i-Limb retails for around $18k (USD). That’s outside of the budget of many individuals, especially in countries where insurance companies do not provide prosthesis coverage (the US being one of them). My big hope is that as motors, sensors, and electronics continue to miniaturize and reduce in price, prosthetics will come down in costs. It will likely take many years, but I suspect that eventually we will see more mechanized prosthesis in use around the world. Or, considering how well Pro-Digits can blend in, maybe we won’t notice them at all.

[photo and video credit: Touch Bionics]

Deka's Luke Arm is in clinical trials. Will it find favor with amputees?

The future of prosthetics isn’t certain, and we’ve seen so many different next generation devices, it’s hard to know which will ultimately arise as the standard. For legs, there are spring like mechanical struts that can outperform their biological counterparts, and there are complex electronic knees and feet that contain narrow artificial intelligence. Prosthetic hands, however, haven’t evolved much in the past 60 years. But that’s about to change. We’ve seen many different robotic hands in development, and one of the most popular in the press has been Deka’s Luke Arm. Dean Kamen, inventor of the Segway scooter and head of Deka, helped design the electronic arm to fit the needs and desires of modern amputees. The Luke Arm went into clinical trials this summer and could become the prosthetic limb of choice for US soldiers returning from Iraq and Afghanistan. Yet, despite the Luke Arm’s media presence (check out the 60 Minutes segment video after the break), I’m not certain it’s going to beat the competition.

For those who missed our first story on Deka’s Luke Arm, I should explain that it is controlled by pads under the feet and attached to shoulders muscles. Like a complex video game, users press on these pads to get the limb to perform desired actions. This is a robust system that allows for a precise level of control. It also takes a while to get used to. Competing prostheses, like i-Limb, use myoelectric sensors that can read nerve signals in muscles. Essentially, you think about moving your missing hand, and the prosthetic performs the action. The two approaches, joystick versus mind-control, seem grossly mismatched in the favor of the myoelectric sensors. How is the Deka arm staying competitive?

Well, largely I think the Luke Arm is winning because it is already able to start clinical trials, has Dean Kamen attached to the project, and is a remarkable piece of machinery. No doubt, the Luke Arm performs very well. It’s customizable, modular, and robust. At only 8 lbs (3.6 kg), it contains electric motors that give it 18 degrees of freedom (the human arm has 22) and pressure control. A vibrating device, called a tactor, gives the user feedback sensation that allows him or her to stop the Luke Arm before it crushes an object. In the video you can see how the device is gentle and sensitive enough to pick up a grape.

As mentioned, the Luke Arm is part of DARPA’s Revolutionizing Prosthetics program. Deka received close to $18 million for the development of its device, but $30.4 million went to John Hopkins Applied Physics Lab for an alternate prosthetic that uses myoelectric sensors. That device, and APL researcher Jonathan Kuniholm, is shown towards the end of the 60 Minutes segment.

DARPA is hedging it’s bets, spreading money around to see which projects will bear fruit. Smart idea. The Luke Arm’s current trial utilizes the control pads we discussed earlier, but Kamen isn’t ruling out the use of myoelectric sensors in the future. Between the APL and Deka, DARPA is bound to get at least one fieldable prosthetic very soon.

But if you’re not a veteran, neither DARPA project may really help you much. The Luke Arm is slated to cost $100,000+, and a similar price is likely for the APL limb. That’s well beyond the means of most amputees if they do not have the insurance coverage provided by the Veteran’s Administration. The i-Limb is offered at a cheaper price (near $18,000) and is already being tested by 600 users. As most amputees are not veterans, I think that the Luke Arm has a good chance of being priced out of a large market share.

Which is why I was very interested in Jonathan Kuniholm’s Open Prosthetics project. The same biomedical engineer working at APL (on the DARPA grant) is an advocate of open source solutions and hopes that a cheap and reliable alternative could be provided for those without the means to spend hundreds of thousands of dollars. Kuniholm gave an amazingly frank and thought-provoking interview to NPR’s Fresh Air earlier in the month. He discussed the budget limitations of amputees, the bias non-amputees have on appearance over function, and the media’s preference for hyperbolic stories (around 11:02). Give it a listen:

After hearing Kuniholm criticize the media for telling just two versions of technology stories (“this device is amazing, it’s going to change everything” or “this device is a horrible waste of money”) I am inclined to give a very measured outlook on the future of prosthetics. The Luke Arm is a great piece of machinery, and it’s likely to be ready soon, but it could be too costly to own and too difficult to operate. Myoelectric devices could offer some amazing possibilities, but they aren’t here yet. Surgically augmented devices, like the Smart Hand, could offer realistic feedback via nerve connections and completely outperform any other limb. But those devices are years from completion. The bottom line is that the first commercially available next-generation upper body prosthetic could be the Luke Arm, but it is certainly not going to be the last. Whichever device eventually sets the standard for limb replacement will have to be adaptable, affordable, and above all functional. May the best hand win.

[photo credit: IEEE Spectrum]
[video credit: 60 minutes via CNET]
[audio credit: NPR Fresh Air]

Even while Dean Kamen and others we have previously reported on work on advanced robotic prostheses, the i-LIMB shows how keeping it simple can still provide amazing improvements to quality of life for amputees.   The i-LIMB uses electrodes placed on the skin of the remaining portion of the patient’s limb, usually on the top and bottom of the forearm.  When the patient moves the muscles that would normally have extended into their hand, the electrodes pick up on electrical signals generated by the muscle movement.   These signals become the basis for individual finger movement within the i-LIMB.

Introduced in 2007 by Scottish company Touch Bionics, the i-LIMB is capable of a variety of unique grip positions that allow the user to balance power and precision as needed.  By extending the index finger alone, patients can type on a keyboard or push buttons.  The user can also grip a key or dinner plate by rotating the thumb to meet the side of the index finger.  The prosthetic is capable of stopping when a sufficient grip is achieved, allowing the patient to grip sensitive objects (e.g. a styrofoam cup) without crushing them.  These more fine-tuned features give the i-LIMB a functionality that enhances the patient’s everyday life.

Patients can choose between a number of cosmetic gloves, including amazingly lifelike skins that blend in naturally with the rest of the body.  The i-LIMB also has a modular construction that allows each finger to be detached by removing one screw.  This way, a digit needing service can be quickly swapped out for a new one, rather than leaving the patient without their prosthetic while it’s being serviced.   The i-LIMB currently costs about $18,000, and is being used by over 600 patients.  More information can be found at the Touch Bionics website.

Check out the i-LIMB in action, as reported by Voice of America:

So what’s next for Touch Bionics?  “We are shortly to release our lower profile i-LIMB Hand which is more appropriate for female and smaller male users,” says Phil Newman, Director of Marketing.  The company is also developing a product for patients missing individual fingers.  “Our next big focus is ProDigits – replacement fingers.  This is a technology for a much larger patient population which has never had a powered finger option before.  We are very excited about this and have a significant number of trial fittings in play.”

Of course, the ideal prosthetic would be hardwired into the nervous system, capable of carrying motor information directly from the brain to the prosthetic and sensory information back up to the brain.  This is exactly the goal of research into Targeted Muscle Reinnervation (TMR) and Targeted Sensory Reinnervation (TSR).  But until these techniques are ready for widespread use, the i-LIMB shows that traditional muscle sensors can improve the quality of life for individuals today.

In the ongoing ethical debates surrounding body augmentation, prosthetics are usually spared accusations of being “unnatural.”  Like antibiotics or hip replacements (to name just a few), prosthetic limbs are widely accepted as beneficial technologies and medical miracles.  Amid the controversies over nanobots or genetic engineering, these less contentious advances should enter into the debate of what a “natural” human being really is.  Natural or not, replacements like the i-LIMB are improving the lives of amputees around the world, and only hint at the possibilities that the future will hold.

Now who can argue with that?