Mar 23, 2019 | Updated: 12:48 PM EDT

Electronic tattoos can be made through graphene and silk

Mar 13, 2019 12:59 PM EDT

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electronic tattoos

E-tattoos, electronic tattoos or epidermal electronics are a thin form of electronics that are wearable. They are soft and lightweight, which allows them to be mounted intimately on human skin for high-fidelity and noninvasive sensing. E-tattoos are touch-sensitive buttons for controlling your smartphone and they can be applied as a stick-on dosimeter to measure UV exposure, graphene-based skin biosensors or lab-on-skin for wearable health monitoring.

During the operation of electronic tattoos, they are exposed constantly to external mechanical inputs like twisting, bending, pressing and cutting, which may cause mechanical damage to the tattoo and it may lead to malfunction.

"We developed our self-healing, biocompatible and multifunctional e-tattoo by incorporating graphene with silk fibroin/Ca2+ films," said Yingying Zhang, Associate Professor in the Department of Chemistry and the Center for Nano and Micro Mechanics at Tsinghua University. "We show that custom-designed and highly flexible e-tattoos can be facilely prepared through screen printing or direct writing of a graphene/silk fibroin/Ca2+ suspension."

The graphene flakes that are distributed in the matrix of the electronic tattoos form an electrically conductive path that is responsive to the changes in the environment, such as humidity, temperature variations, and strain, endowing the electronic tattoo with high sensitivity to multi-stimuli.

What is remarkable about this is that the electronic tattoo can be healed with an efficiency rate of 100% even after being fractured within 0.3 seconds, it can be healed by wetting it with a droplet of water because the hydrogen and the coordination can help the reformation and it bonds at the fracture interface.

"Based on the superior capabilities of our e-tattoos, we believe that such skin-like devices hold great promise for manufacturing cost-effective artificial skins and wearable electronics," notes Zhang.

The silk fibroin that is used by the researchers is a natural protein material that is produced by silkworms. It has been identified as suitable for electronic applications that are wearable because of its mechanical durability, all-aqueous processing, tunable secondary structure and good biocompatibility.

Despite the massive potential of silk fibroin for use as e-tattoos and wearable electronics, its applications in electronics that are wearable are limited to its use as a substrate, rather than its use as the active functional material.

Graphene shows great potential for e-tattoo applications because it is strong and stable, mechanically and electrochemically plus it is biocompatible. Graphene materials can be functionalized through different chemical and physical approaches, providing a lot of room for tailoring the properties and the performance of sensors that are graphene-based.

"The integration of graphene materials and silk has been explored previously, but the majority of studies focuses on mechanical enhanced materials," notes Zhang. "We found that silk/graphene composite materials are highly promising for emerging epidermal electronics."
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