Aug 12 2011

Electronic Skin

A cool study has been published in Science detailing the development of an electronic second skin. Zhenqiang Ma details the technological problems and potential solutions to developing electronics that are thin and flexible, like human skin, and in fact can be placed on the skin for medical purposes.

We have seen this type of technology coming for some years – the promise of flexible electronics. Silicon chips are fine, but when you can bend a transistor that opens up a lot of potential uses.

Ma details the properties that are needed for second-skin electronics. Flexible electronics having many possible uses, such as artificial skin for robots. But if you want to attach flexible electronics to human skin for medical monitoring you need additional features:

Attaching electronic skin to natural skin is more difficult than attaching it to robots or prosthetics. Natural skin is soft and delicate and already has touch-sensing functions. The electronic skin that can be used for physiological monitoring must have a supporting layer with mechanical properties that match those of natural skin to avoid any discomfort resulting from long wearing. The electronic skin must not be too thick, too rigid, too hard, or too heavy, but must have conformal contact, intimate integration, and adequate adhesion with the natural skin.

The solution was to have the semi-conductors, insulators, and other components of a typical transistor integrated circuit as a nano-wire mesh, coiled in a “serpentine” fashion. This allows the layer to stretch and bend flexibly. Then you attach it to a supportive layer that has the same strength and flexibility as human skin. Keep the whole thing thin enough for comfort – and you have a portable electrode suitable for medical applications.

These second-skin electrodes can be kept on the skin for much longer (it is hoped) than traditional electrodes, which tend to cause skin irritation and are often bulky. This could allow for comfortable long term heart or brain wave (EEG) monitoring.

And those are just the most obvious applications. Once you have a computer chip that can be worn comfortably for a long time other applications will open up. Essentially this could allow us to close the loop on automatic drug-delivery systems. Second-skin computer chips could monitor some physiological parameter, and then respond with an appropriate dose of a drug or some other response.

This could also revolutionize prosthetics (artificial replacement body parts) – if you can safely keep working electrodes attached to the skin, they can be used to monitor nerve and muscle activity which can then be used to control or modulate robotic prosthetics.

We could further combine this technology with the progressing technology of controlling robotic and computer devices with the brain via scalp electrodes. Subject can learn to control devices by thought alone – EEG activity is picked up by electrodes, calibrated and then interpreted by a computer, which then translates the EEG activity into a desired action.

The primary limitation on this technology is having sufficient electrodes to monitor the EEG. Implanted wires work best, but this is invasive and risky. Scalp surface electrodes are safer, but the information is highly degraded compared to implanted wires – and you have to wear a massive helmet of electrodes, so not suitable for everyday use.

But – with second skin electrodes, it is at least conceivable that a person can be fitted with a large number of small electrodes that could provide a detailed EEG recording wirelessly, that will be safe, comfortable, and aesthetic. Using this setup to control an artificial limb, or an external robot or computer could then be feasible long term outside the lab.

As electronics get smaller, more flexible, and more energy efficient we will begin to see more and more applications, including interfacing electronics with biology. I don’t know if the current approach will predominate, but it is a nice proof of concept.

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