Smart move: artificial skin gets in the game

Next gen multisensory, smart, artificial skin developed using 3-in-1 hybrid material.

A team at the Institute of Solid State Physics at TU Graz has developed “smart skin” which is very similar to human skin, sensing pressure, humidity and temperature simultaneously, as well as being able to produce electronic signals. This work could signpost the way to more sensitive robots or more intelligent prostheses.

Longevity.Technology: As well as being our largest sensory organ, the skin forms a protective barrier around our bodies. Providing constant feedback, skin “feels” several sensory inputs at the same time and reports information about humidity, temperature and pressure to the brain. Smart skin could monitor human physiological signals like breathing, pulse and temperature, or detect dehydration. As an avenue for intelligent perception, smart skin could be used in artificial prostheses, intelligent robots and human-machine interaction, improving healthspan and extending lifespan.

As well as being our largest sensory organ, the skin forms a protective barrier around our bodies. Providing constant feedback
Smart skin is a wafer-thin material that reacts simultaneously to force, moisture and temperature with extremely high spatial resolution and emits corresponding electronic signals.

For Anna Maria Coclite, ERC grant winner and researcher at the Institute of Solid State Physics at TU Graz, a material with such multisensory properties was: “A kind of ‘holy grail’ in the technology of intelligent artificial materials. In particular, robotics and smart prosthetics would benefit from a better integrated, more precise sensing system similar to human skin [1].”

With her team, she has now succeeded in using a novel process to develop a three-in-one hybrid material smart skin for the next generation of artificial, electronic skin; the result of this pioneering research has now been published in the journal Advanced Materials Technologies.

As delicate as a fingertip

For almost six years, the Graz team worked on the development of smart skin as part of Coclite’s ERC project Smart Core. With 2,000 individual sensors per square millimetre, the hybrid material is even more sensitive than a human fingertip. Each of these sensors consists of a unique combination of materials: an smart polymer in the form of a hydrogel inside and a shell of piezoelectric zinc oxide.

For almost six years, the Graz team worked on the development of smart skin as part of Coclite's ERC project Smart Core.
The research team that developed Smartskin: (from left to right) Philipp Schäffner, Materials Institute of Joanneum Research, Anna Maria Coclite, Institute of Solid State Physics of TU Graz, Barbara Stadlober, Materials Institute of Joanneum Research, and Taher Abu Ali, also Institute of Solid State Physics of TU Graz.

Coclite explains: “The hydrogel can absorb water and thus expands upon changes in humidity and temperature. In doing so, it exerts pressure on the piezoelectric zinc oxide, which responds to this and all other mechanical stresses with an electrical signal [1].”

The result is a wafer-thin material that reacts simultaneously to force, moisture and temperature with extremely high spatial resolution and emits corresponding electronic signals [2].

“The first artificial skin samples are six micrometres thin, or 0.006 millimetres. But it could be even thinner,” says Coclite [1]. In comparison, the human epidermis is 0.03 to 2 millimetres thick. The human skin perceives things from a size of about one square millimetre, but the smart skin has a resolution that is a thousand times smaller and can register objects that are too small for human skin (such as microorganisms).

Material processing at the nanoscale

The individual sensor layers are incredibly thin, but packed with sensor elements that cover the entire surface. This was possible by using what the researchers claim is a unique process – combining three known methods from physical chemistry for the first time. The team combined a chemical vapour deposition for the hydrogel material, an atomic layer deposition for the zinc oxide and nanoprint lithography for the polymer template [2]. The lithographic preparation of the polymer template was the responsibility of the research group “Hybrid electronics and structuring” headed by Barbara Stadlober, part of Joanneum Research’s Materials Institute based in Weiz.

According to the research team, several fields of application are now opening up for the skin-like hybrid material. In healthcare, for example, the sensor material could independently detect microorganisms and report them accordingly. Also on the cards are prostheses that give the wearer information about temperature, humidity or what things feel like, or robots that can perceive their environment more sensitively.

When it comes to scalability, smart skin scores with a decisive advantage: the sensory nanorods – the “smart core” of the material – are produced using a vapor-based manufacturing process. This process is already well established in production plants for tech like integrated circuits, for example, meaning the production of smart skin could be easily scaled and implemented in existing production lines.

The properties of smart skin are now being optimised even further. Anna Maria Coclite and her team – here in particular the PhD student Taher Abu Ali – want to extend the temperature range to which the material reacts and improve the flexibility of the artificial skin.

[1] https://www.tugraz.at/elektronische-haut-physikerin-der-tu-graz-entwickelt-multisensorisches-hybridmaterial0/
[2] https://onlinelibrary.wiley.com/doi/10.1002/admt.202200246

Photograph: Lunghammer – TU Graz

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