Electronic Skin: Advancements and Opportunities

Dr S.S. Verma is a professor at Department of Physics, Sant Longowal Institute of Engineering and Technology, Sangrur, Punjab

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The various types of artificial electronic skins being developed offer amazing properties and applications

Skin plays an important role in mediating our interactions with the world. Specifically, human skin can sense pressure and temperature, stretch, and heal itself. Electronic skin is a thin electronic material that mimics human skin in one or more ways. Recreating the properties of skin using electronic devices could have profound implications in various fields like robotics, prosthetics and medicine. The artificial skin could one day be used on robotic hands capable of detecting diseases or intoxication of humans via touch.

The pursuit of artificial skin has inspired innovations in materials to imitate skin’s unique characteristics, including mechanical durability and stretch ability, biodegradability, and the ability to measure a diversity of complex sensations over large areas. New materials and fabrication strategies are being developed to make mechanically compliant and multifunctional skin-like electronics, and improve brain-machine interfaces that enable transmission of skin’s signals into the body.

Scientists and engineers have made progress toward materials that can detect pressure, blend with surroundings, measure body temperature, and do much more. Here is a summary.

Ulsan National Institute’s electronic skin that can detect changes in both temperature and pressure
Ulsan National Institute’s electronic skin that can detect changes in both temperature and pressure

Self-healing electronic skin

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Stanford University researchers have developed an electronic skin capable of healing itself by combining a self-healing plastic and nickel, a conductive metal. Unlike self-healing polymers developed by other researchers, this skin did not require a high temperature or UV light to activate.

The individual plastic molecules of the skin break apart relatively easily, but the bonds also easily reform. Cut pieces healed to 75 per cent strength within a few seconds and fully in less than 30 minutes when pressed together at room temperature. Additionally, the process could be repeated many times—in experiments the material showed near-perfect healing after 50 breaks. Other self-healing materials alter their structures in the process and thus can heal only once.

In addition to being self-healing, the electronic skin was pressure-sensitive and very flexible. It was the first material to exhibit all these properties at the same time. It was also the first conductive self-healing polymer. The e-skin could detect both downward pressure and pressure from bending; thus, in principle, it could detect both the pressure and angle of a normal human handshake.

According to the research team, the material could be useful in prosthetics and creating self-healing wires for electronic devices.

Lighting electronic skin

Researchers from the University of California at Berkeley have created an electronic skin that lights up when touched. Pressure triggered a reaction in the skin that lit up blue, green, red and yellow LEDs; as pressure increased the lights got brighter.

The material was composed of synthetic rubber and plastic, and was thinner than a piece of paper. Sandwiched between layers, organic LEDs were lit by semiconductor-enriched carbon nanotubes and a conductive silver ink. The skin was made up of hundreds of circuits, each of which contained a pressure sensor, a transistor and a tiny LED. Pressure changed the resistance of the sensor, thereby changing the amount of electricity flowing into the LED.

The team suggested that the invention could be useful in skin for prosthetic limbs and robotics. One of the major problems with these kinds of light films in the past, though, was that these only lasted a matter of hours when exposed to normal air.

Making any piece of ultra-stretchy electronics often involves sandwiching materials together to produce something with the right properties, whether it’s for a red light or a method of sensing pressure. In this case, the researchers added a new protective coating, called a passivation layer, to various kinds of e-skin. The coating kept out oxygen and water vapour well enough to keep the light working for several days. Researchers report that this power LED film also produced less heat and consumed less power than previous efforts. The coating they used can also work on e-skin that does more than just light up.

Electronic skin that lights up when touched
Electronic skin that lights up when touched

Sweating electronic skin

A Northwestern University research team has developed a first-of-its-kind soft, flexible microfluidic device that easily adheres to the skin and measures the wearer’s sweat to show how his body is responding to exercise.

A little larger than a quarter and about the same thickness, the simple, low-cost device analyses key biomarkers to help the user decide quickly if any adjustments, such as drinking more water or replenishing electrolytes, need to be made or if something is medically awry.

Designed for one-time use of a few hours, the device, placed directly on the skin of the forearm or back, even detects the presence of a biomarker for cystic fibrosis. In the future, it may be more broadly used for disease diagnosis.’

Northwestern University’s flexible device measures the wearer’s sweat to analyse his key biomarkers
Northwestern University’s flexible device measures the wearer’s sweat to analyse his key biomarkers

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