Bionic Hand Wired To Nerves Can "Feel" When Touched 42
An anonymous reader writes in with a breakthrough in prosthetics. "The first bionic hand that allows an amputee to feel what they are touching will be transplanted later this year in a pioneering operation that could introduce a new generation of artificial limbs with sensory perception.
The patient is an unnamed man in his 20s living in Rome who lost the lower part of his arm following an accident, said Silvestro Micera of the Ecole Polytechnique Federale de Lausanne in Switzerland.
The wiring of his new bionic hand will be connected to the patient’s nervous system with the hope that the man will be able to control the movements of the hand as well as receiving touch signals from the hand’s skin sensors."
Missing some details (Score:5, Informative)
What it appears they are going to do is implant some wires into the man's residuum. These wires - electrodes - will have two purposes:
In conventional motor-driven, upper-limb prostheses, particularly below-the-elbow, the control signals are measured using surface EMGs (ElectroMyoGraphic sensors). These aren't measuring nerve firings, per se, but rather the electrical activity of actual muscle contractions (in the forearm). This is done because the actual motor nerves are pretty tiny, and the signal in them is fairly small. The muscle, on the other hand, is much easier to locate, and it acts as a natural amplifier of what the nerve tells it to do. It's the difference between probing a tiny signal wire coming out of your MP3 player and picking up the sound that is resonating in the speaker housing.
The downside of using surface EMGs is that, by measuring electrical potentials across several cm of skin and muscle, it is hard to pick up on individual muscle contractions. So, it is generally not possible to pick up on just the muscle that flexed/extended the index finger. The best you can usually do is pick up on the flexion/extension signals for all finger muscles or the wrist. Another downside is that the EMGs are usually mounted to the socket - the molded plastic or composite structure that mechanically interfaces the prosthesis to the residuum. As the wearer moves around and sweats, the EMGs can shift over the skin surface, which degrades the signal strength and specificity.
By implanting EMG electrodes under the skin, you can mostly eliminate the problems of the having the electrodes shifting, because they'll move with the tissue they are measuring. You may also be able to get more localized measurements (crosstalk is a difficult problem), and so get more than 1-2 channels of control input. This approach is not exactly new, but neither is it widespread. Amputees are, naturally, a bit wary of invasive procedures - they don't want to risk screwing up what they have left. The other downside is that, at least in this case, they are opting for transdermal electrodes - wires poking through the skin, which could have long-term drawbacks. Some work is being done with fully implanted EMGs that can be probed using near field technologies - RFID in your muscles - but that is still a work in progress.
Stimulating nerves to provide sensory feedback is, likewise, not exactly new, but hasn't made it into clinical practice. There have been anecdotes about patients who have undergone targeted nerve reinnervation who, when you poke them in a certain place on their pectoral muscle, report "feeling" a sensation in their lost hand. Again, going to implanted electrodes allows you the chance to have must greater specificity.
Aside from the invasive nature of the procedure, my main concern with this project is its longevity. How long can the electrodes exist within the body? Will you still be able to get or produce a worthwhile signal after 1 month, 6 months, 10 years? The prosthesis can be repaired and replaced over time, but tinkering around with the electrodes may not be feasible. I also have some concerns about the durability of the sensing elements in the prosthetic hand, but that is more straightforward engineering than anything else.