Hand with electronic skin

Touch is the first sense we acquire and has been shown to play a crucial role in physical and mental health. The nerve cells in our skin allow us to experience the several experiences of touch such as a cold splash of water, the tug of a strong breeze or the heat from your coffee mug. Scientists are trying to develop electronic skin to help robots and prosthetic devices to attain these abilities.

Researchers report a new method in ACS Applied Materials & Interfaces that creates an ultrathin, stretchable electronic skin, which could be used for prosthetics, robotics, virtual reality and even wearable health monitors. The main challenge is to transfer ultrathin electrical circuits onto complex 3D surfaces. Moreover, the electronics have to be bendable and stretchable enough to allow movement. Current methods for producing these electronics are slow, expensive and require sophisticated equipment and techniques.

In the new approach the researchers patterned a circuit template on to a sheet of transfer tattoo paper with an ordinary desktop laser printer.

Printing circuit with laser printer

Then, they coated the template with silver paste which stuck only to the printed toner ink and wiped away the excess silver.

Ag epoxy deposition

Driving silver epoxy

On top of the silver paste the team deposited a gallium indium liquid metal alloy that increased the flexibility and electrical conductivity of the circuit.

E-GaIn deposition

Subsequently, they added external electronics such as microchips with silver epoxy or conductive glue made of vertically aligned magnetic particles embedded in a polyvinyl alcohol gel.

Placing components with silver epoxy

The researchers used water to help transfer the electronic tattoo to 3-D objects. This was done by immersing the object in a tub of water and then placing the circuit on the surface of the water.

Immersing object in tub of water

The paper backing of the tattoo is separated from the carrier film which floated on the surface of the water.

Finally, when the researchers lifted the object out of the water, the circuit adhered to the contours of the object.

Circuit adhered to the contours of the object

This electronic skin remains functional under bending, folding, twisting, and strains up to about 30% (similar to human skin). They can adapt and adhere to highly curved 3-D surfaces, like a model of a human brain or an apple.

Various applications of the new method include controlling a robot prosthetic arm, incorporating proximity sensors into a 3D model of a hand and epidermal bio monitoring.

The research was performed in collaboration between Carnegie Mellon's Soft Machines Lab and the Institute of Systems and Robotics at the University of Coimbra in Portugal.

The findings were published in the paper, "EGaIn-Assisted Room-Temperature Sintering of Silver Nanoparticles for Stretchable, Inkjet-Printed, Thin-Film Electronics," in Advanced Materials.

To know more about electronic tattoos and their applications check out this video