Soft, stretchy, slimline and strong
electronics could accelerate the arrival of artificial skin.
A material that
mimics human skin in strength, stretchability and sensitivity could be used to collect
biological data in real time. Electronic skin, or e-skin, may play an important
role in next-generation prosthetics, personalized medicine, soft robotics and
artificial intelligence.
"The ideal
e-skin will mimic the many natural functions of human skin, such as
sensing
temperature and touch, accurately and in real time," says KAUST postdoc
Yichen Cai. 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.
However, 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.
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“The landscape of skin electronics keeps
shifting at a spectacular pace,” says Cai. “The emergence of 2D sensors has
accelerated efforts to integrate these atomically thin, mechanically strong
materials into functional, durable artificial skins.”
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.
“Hydrogels are more
than 70 percent water, making them very compatible with human skin tissues,” explains
Shen. By prestretching
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 centimeters 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 5,000 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,” says Shen, “which mimics the elasticity
and rapid recovery of human skin.”
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.
“One remaining obstacle to the widespread use
of e-skins lies in scaling up of high-resolution sensors,” adds group leader Vincent Tung; “however, laser-assisted
additive manufacturing offers new promise.”
“We envisage a future for this technology
beyond biology,” adds Cai. “Stretchable sensor tape could one day monitor the
structural health of inanimate objects, such as furniture and aircraft.”
References
Cai,
Y., Shen, J., Yang, C., Wan, Y., Tang, H., Aljarb, A.A., Chen, C., Shao, Y.,
Han, Y., Jonas, S.J., Dong, X. & Tung, V. Multifunctional electronic skin sensors
with ultrabroad working range. Science Advances 6 (2020) | article
