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How engineers are giving us a second, smarter skin

Amit Katwala

(Credit: iStock)
(Credit: iStock)

The skin is our heaviest, but arguably most underrated, organ. It’s equipped with a complex patchwork of nerves and pressure sensors, allowing us to feel our way around the world with accuracy and confidence. It could be about to get even better.

Groups of scientists and engineers all over the world are working on wearable technology that promises to upgrade our skin, by using it as a power source for smart devices, helping doctors monitor our vital signs, or giving those with prosthetics a sense of touch.

Researchers in South Korea and the United States, for example, have developed an electronic skin that can track heart rate, respiration, muscle movement and other health data, and wirelessly transmit it to a smartphone.

It’s a soft silicon patch about four centimetres wide that can be stuck almost anywhere on the body, but that contains remarkable complexity. It contains about 50 components connected by a network of 250 tiny wire coils. Unlike other wearables, it conforms to the body, and stretches and bends without breaking. The design, say researchers Kyung-In Jang of the Daegu Gyeongbuk Institute of Science and Technology and John A Rogers of Northwestern University in Illinois, is influenced by nature – the wires are like a vine, connecting up the different sensors and transmitters like leaves.

Flexibility and power

One of the challenges with wearables that stick to the skin is building in enough flexibility so that they’re not uncomfortable when we move around. Silicon is one common solution, but Chinese researchers think silk might be a better one.

“There is a whole world of possibilities for silk sensors at the moment. Silk is the ideal material for fabricating sensors that are worn on the body,” says Yingying Zhang at Tsinghua University in Beijing.

Zhang and colleagues have been researching ways of improving the electrical conductivity of silk so that it can be used in flexible sensors. They took two very different approaches.

The first involved treating the silk at extremely high temperatures in an inert gas environment to infuse it with some electrically conductive graphitized particles. Using this technique, they were able to create strain sensors, pressure sensors and a sensor capable of measuring temperature and pressure simultaneously – all made of flexible silk.

Another more outlandish attempt involved feeding graphene or carbon nanotubes to silkworms so that the substances were naturally incorporated into the silk when they produced it. That technique hasn’t worked yet, but Zhang’s team is still experimenting with it.

If wearables are going to truly become like a second skin, we need better ways of powering them than heavy and awkward batteries. At the University of San Diego, engineers are working on a way of using the skin itself as a source of power. They’ve developed stretchable fuel cells that can extract energy from sweat to power electronics such as LEDs or Bluetooth transmitters.

Their device is made from printed carbon nanotubes, and also has biofuel cells containing an enzyme that breaks down the lactic acid in our sweat to generate a current. The device was able to power an LED when the person connected to it pedalled on an exercise bike.

What’s next?

Most researchers see potential uses for their devices in the medical industry, where doctors could get live information from patients wearing more comfortable sensors. “Combining big data and artificial intelligence technologies, the wireless biosensors can be developed into an entire medical system which allows portable access to collection, storage and analysis of health signals and information,” says Jang.

Zhang agrees. "One possibility we foresee is for the sensors to be used as an integrated wireless system that would allow doctors to more easily monitor patients remotely so that they can respond to their medical needs more rapidly than ever before,” she says.

Jang says this could be particularly useful in remote areas. “We will continue further studies to develop electronic skins which can support interactive telemedicine and treatment systems for patients in blind areas for medical services such as rural houses in mountain villages,” he said.

Researchers in South Korea have developed a flexible, wearable silicon patch

In the future, smart skin could also be used to give amputees a sense of touch through their prosthetic limbs, or allow robots to feel ‘pain’. That’s what Ravinder Dahiya is trying to do in his lab at the University of Glasgow. “It is very desirable,” he says. “Consider fatigue – fatigue is also a pain. If you hold a 10kg weight in one hand for one or two minutes you start experiencing a slow pain. We would like to see electronic skin on a robotic platform.”

Dahiya says that such skin could be applied to humanoid robots in factory settings to measure the amount of stress, or even to larger structures such as cranes. In future, it could even change colour depending on the amount of force applied – just as human skin will turn pale under pressure as the blood flows away. “Electronic skin becomes a medium to give you that feedback,” he says. Others are working on ways to give robots a sense of touch.

So, while researchers are developing smart skins for humans that will make us a bit more like robots, the process is also going the other way. We’ll become more like robots – with wires and sensors attached to our skin – while robots will become a bit more human.

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