E-Dermis: Feeling At Your (Prosthetic) Fingertips

When we lose a limb, the brain is really none the wiser. It continues to send signals out, but since they no longer have a destination, the person is stuck with one-way communication and a phantom-limb feeling. The fact that the brain carries on has always been promising as far as prostheses are concerned, because it means the electrical signals could potentially be used to control new limbs and digits the natural way.

A diagram of the e-dermis via Science Robotics.

It’s also good news for adding a sense of touch to upper-limb prostheses. Researchers at Johns Hopkins university have spent the last year testing out their concept of an e-dermis—a multi-layer approach to expanding the utility of artificial limbs that can detect the curvature and sharpness of objects.

Like real skin, the e-dermis has an outer, epidermal layer and an inner, dermal layer. Both layers use conductive and piezoresistive textiles to transmit information about tangible objects back to the peripheral nerves in the limb. E-dermis does this non-invasively through the skin using transcutaneous electrical nerve stimulation, better known as TENS. Here’s a link to the full article published in Science Robotics.

First, the researchers made a neuromorphic model of all the nerves and receptors that relay signals to the nervous system. To test the e-dermis, they used 3-D printed objects designed to be grasped between thumb and forefinger, and monitored the subject’s brain activity via EEG.

For now, the e-dermis is confined to the fingertips. Ideally, it would cover the entire prosthesis and be able to detect temperature as well as curvature. Stay tuned, because it’s next on their list.

Speaking of tunes, here’s a prosthetic arm that uses a neural network to achieve individual finger control and allows its owner to play the piano again.

Thanks for the tip, [Qes].

Replacing A Phantom Limb With A Kinect

Nearly everyone has heard of phantom limb syndrome. It occurs sometimes after a limb is amputated, but the mind of the patient still thinks that the limb is attached. Generally regarded as a mix-up in the wiring of the damaged nerves, a phantom limb can be very painful. [Ben] has been working on a way to alleviate some of the pain and frustration associated with a phantom limb and fortunately for us he went for a Kinect, VR goggles, and gyroscope build.

Today, most therapies for phantom limb syndrome use a Ramachandran Mirror Box. The theory behind the mirror box is pretty simple – if someone recently lost a hand, just insert one hand in one side of the box and the arm stump on the other side. Looking into the box from the side with the good hand will trick the patient’s brain into thinking the amputated hand is still there. It’s a good therapy that has been very successful, but [Ben] thought he could do something that is a little more immersive.

[Ben]’s project uses a Kinect and VR goggles to put the patient in a virtual environment. With the help of a few gyroscopes, the patient gets a virtual representation of their whole self projected into their goggles. The technique isn’t terribly different from VR phobia treatment, although there’s much more electronics and math involved in [Ben]’s build. The first test subject said his pain was going down, so it looks like he might have a success on his hand (no pun intended).

Check out the demos of [Ben]’s treatment plan after the break.

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