Printing Electronics Directly on Delicate Surfaces—Like the Back of Your Hand

The gentle, low-temperature technique prints electric tattoos on skin and transistors on paper

3 min read
Image of finger printing
Photo: Aaron Franklin and Nick Williams/Duke University

Nick Williams didn’t ask permission. The graduate student just stuck his pinky finger under the printer and watched it paint two silver lines on his skin. When printing was complete, Williams put a small LED light at one end of the lines and applied voltage to the other. He smiled as the light glowed.

Williams showed the electronically active tattoo to his advisor, Duke University electrical engineer Aaron Franklin. Since Williams barely felt the printing, and the silver washed off with soap and water, they tried it again.

Flexible electronics are having a moment. The sheer range of devices developed recently demonstrates the scope and speed of the field, including patches to communicate with robots, wearables to reverse baldness or detect heartbeats, and solar cells that can be sewn into clothing.

But Williams’s new temporary tattoo was a novelty because electronic components aren’t usually printed onto skin or other sensitive materials. Printed electronics typically require post-processing such as oven baking or chemical baths to remove residual liquids and unwanted materials that interfere with electric fields.

In two recent papers, Franklin, Williams and colleagues at Duke demonstrate a low-temperature technique for printing electrical components—including leads and transistors—onto delicate surfaces such as apples, human skin and paper, with no post-processing required.

“Ultimately it doesn’t matter if it’s paper or plastic or what-not, you want to be able to put your surface in, add printed, functional electronics to that surface, and away you go,” says Franklin. The new technique enables researchers to print electronic components onto a wide range of materials and reduces overall production complexity and time, he says.

paper and plastic transitors Paper and plastic transistors Photo: Aaron Franklin/Duke University

In a July paper in the journal Nanoscale, the team printed silver nanowire ink onto a variety of surfaces using an aerosol jet printer, which turns liquid ink into an aerosol form by infusing it with an inert gas such as nitrogen.

The silver nanowire ink, as opposed to silver nanoparticles or other conductive materials, enabled the team to print conductive lines at near-room temperature, which made Williams hypothesize that it should work on skin. Additionally, silver nanowires are biocompatible, while silver nanoparticles—a commonly used material in other printed electronics—raise toxicity concerns.

In a second paper, published this month in ACS Nano, Franklin and colleagues created flexible thin-film transistors by printing layers of semiconducting carbon nanotubes, silver nanowire ink, and a graphene-like insulating ink called hexagonal boron nitride (h-BN). “We honestly didn’t know [if it would work], so we just tried,” Franklin told IEEE Spectrum.

When the transistors were complete, the team baked a few at high-temperatures to see if it would improve the performance. “They did not actually get better,” says Franklin. That surprise suggests that low-temperature printing without post-processing will not diminish the performance of electronics printed in this way.

Numerous other labs are exploring the use of flexible electronics as biosensors, with impressive techniques for making and transferring electronics to flexible, tattoo-like stickers, says Franklin. Therefore, the low-temperature printing could perhaps be most useful for bespoke applications, such as custom bandages made for patients on-the-spot to monitor a set of biological indicators requested by a doctor.

Last year, Franklin’s spinout company, Tyrata, Inc., raised $4.5 million to commercialize carbon nanotube sensors to monitor tire tread. While Franklin has no immediate plans to start a company related to the low-temperature printing, the lab is working to improve the performance of the devices and continue to lower the printing temperature, he says. Plus, Franklin plans to start developing biosensors.

Image of leaf printed with Duke logo Photo: Aaron Franklin/Duke University

“We don’t want to just print conductive traces onto human skin,” says Franklin. “We want to actually show we can do a full printing on any surface with useful, functional biosensing devices.”

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This CAD Program Can Design New Organisms

Genetic engineers have a powerful new tool to write and edit DNA code

11 min read
A photo showing machinery in a lab

Foundries such as the Edinburgh Genome Foundry assemble fragments of synthetic DNA and send them to labs for testing in cells.

Edinburgh Genome Foundry, University of Edinburgh

In the next decade, medical science may finally advance cures for some of the most complex diseases that plague humanity. Many diseases are caused by mutations in the human genome, which can either be inherited from our parents (such as in cystic fibrosis), or acquired during life, such as most types of cancer. For some of these conditions, medical researchers have identified the exact mutations that lead to disease; but in many more, they're still seeking answers. And without understanding the cause of a problem, it's pretty tough to find a cure.

We believe that a key enabling technology in this quest is a computer-aided design (CAD) program for genome editing, which our organization is launching this week at the Genome Project-write (GP-write) conference.

With this CAD program, medical researchers will be able to quickly design hundreds of different genomes with any combination of mutations and send the genetic code to a company that manufactures strings of DNA. Those fragments of synthesized DNA can then be sent to a foundry for assembly, and finally to a lab where the designed genomes can be tested in cells. Based on how the cells grow, researchers can use the CAD program to iterate with a new batch of redesigned genomes, sharing data for collaborative efforts. Enabling fast redesign of thousands of variants can only be achieved through automation; at that scale, researchers just might identify the combinations of mutations that are causing genetic diseases. This is the first critical R&D step toward finding cures.

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