Researchers create a strong and stretchy e-skin

Thursday, 28 January, 2021

A material that mimics human skin in strength, stretchability and sensitivity could be used to collect biological data in real time, according to researchers at the King Abdullah University of Science and Technology (KAUST) who have created a durable new kind of electronic skin (e-skin).

As explained by KAUST postdoc Yichen Cai, “The ideal e-skin will mimic the many natural functions of human skin, such as sensing temperature and touch, accurately and in real time.” However, making suitably flexible electronics that can perform such delicate tasks while also enduring the bumps and scrapes of everyday life is challenging, and each material involved must be carefully engineered.

Most e-skins are made by layering an active nanomaterial (the sensor) on a stretchy surface that attaches to human skin. But the connection between these layers is often too weak, which reduces the durability and sensitivity of the material; alternatively, if it is too strong, flexibility becomes limited, making it more likely to crack and break the circuit.

A team led by Cai and colleague Jie Shen has now created a durable e-skin using a hydrogel reinforced with silica nanoparticles as a strong and stretchy substrate and a 2D titanium carbide MXene as the sensing layer, bound together with highly conductive nanowires. Their development has been detailed in the journal Science Advances.

“Hydrogels are more than 70% water, making them very compatible with human skin tissues,” Shen said. By pre-stretching the hydrogel in all directions, applying a layer of nanowires and then carefully controlling its release, the researchers created conductive pathways to the sensor layer that remained intact even when the material was stretched to 28 times its original size.

Their prototype e-skin could sense objects from 20 cm away, respond to stimuli in less than one-tenth of a second and, when used as a pressure sensor, could distinguish handwriting written upon it. It continued to work well after 5000 deformations, recovering in about a quarter of a second each time.

“It is a striking achievement for an e-skin to maintain toughness after repeated use which mimics the elasticity and rapid recovery of human skin,” Shen said.

This type of e-skin could monitor a range of biological information, such as changes in blood pressure, which can be detected from vibrations in the arteries, and movements of large limbs and joints. This data can then be shared and stored on the cloud via Wi-Fi. It could also play an important role in next-generation prosthetics, personalised medicine, soft robotics and artificial intelligence.

“One remaining obstacle to the widespread use of e-skins lies in scaling up of high-resolution sensors,” noted group leader Vincent Tung. “However, laser-assisted additive manufacturing offers new promise.”

“We envisage a future for this technology beyond biology,” Cai concluded. “Stretchable sensor tape could one day monitor the structural health of inanimate objects, such as furniture and aircraft.”

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