New artificial, bionic hands start to get real feelings:
Simple tasks, like plucking the stem off a cherry, are still monumental challenges for artificial hands. With a bill of materials perhaps a few hundred components long, it is not surprising that their functionality is low compared with one assembled from trillions of components. A new prosthetic bionic hand, designed and built by researchers at Case Western University is now capable of using measurements from 20 sensor points to control the grip force of its digits. Incredibly, the sensor data is linked directly to the sensory nerves in the patient’s forearm. The control for the grip closure is then extracted myoelectrically from the normal biological return loop to the muscles in the forearm.
The key to making this device work is an instrument known as a cuff electrode. While these electrodes have been under development for decades for use as stimulators for the optic nerve, it has been difficult to get them to reliably stimulate axons for extended periods of time. The new cuffs used here are able to target individual groups of axons without actually penetrating the protective sheaths that segregate particular groups of them. As you can see in the picture below, a nerve has a complex cross section where individual channels exchange members continuously along their length. When multiple cuffs are eventually used on the same nerve, this particular feature of nerve bundles will come in handy because it provides a way to target different axons at different points in the nerve.
If for example, the first cuff stimulates more axons than is actually desired, the second cuff could, at least in theory, provide sub-threshold current to shunt particular axons that can be better targeted at the second cuff — in effect acting as firefighters do when they intentionally burn select areas to preempt the advance of an out-of-control forest fire, only a lot faster. In the forearm, there are three major nerves, the median, radial, and ulnar, which connect both motor and sensory axons within various funiculi. Just to clarify here, a nerve bundle, or funiculus, is in turn composed of several smaller nerve fasciculi. For now, the researchers use just one cuff per nerve, with the data from the 20 sensor points shared between them.
The key to targeting axons deep in the interior of the nerve is to filet them out like the header on a ribbon connector by using a flat cuff, instead of the traditional round design. It appears that the nerves can handle this seeming trauma because the two patients outfitted with these devices have shown good performance now for 18 months. We just heard that the world’s first official cyborg, Neil Harbisson, had his cybernaut status minted with a government seal of approval. He is even permitted to have his passport photo taken with head-mounted hardware. Provided this new bionic hand continues to function for the long haul, it seems that at least two more names might soon be added to that list.