By Katie Elyce Jones. Photos by Shawn Poynter.
Technology is constantly changing the way we approach everyday health. Patients and health care professionals now rely on portable diagnostic tests to measure blood glucose levels, monitor heart rates, and predict epileptic seizures. New wearable electronics even let doctors observe a patient’s condition from a distance.
Ideally, these devices lower health care costs by providing convenient at-home care to people who might otherwise have to visit a clinic or hospital multiple times for diagnosis, treatment, and checkups. But the manufacturing costs of these emerging small-scale tools must be overcome to make them widely available, especially in areas with limited access to health care services.
That’s why Anming Hu, assistant professor of mechanical, aerospace, and biomedical engineering, set out to create a way to produce electronic circuitry using an inexpensive, abundant material: paper.
“We were thinking about what the public needs. If something can be cheaper and not depend on delicate or complicated devices, that’s what we need,” Hu said. “Fabrication should be easy, cheap, and not involve many steps.”
Relying on his background in nanomanufacturing, Hu designed a simple process to create a flexible sensor by applying conductive ink that carries electricity along the printed circuit design to regular paper. The results were published in the journal ACS Applied Materials and Interfaces in November 2014.
“I really think this printing technique has a bright future,” Hu said. “We’re ready to work with industry partners to find new commercial applications.”
One potential application could benefit diabetics who rely on daily finger pricks to test their blood sugar levels. With a paper circuit enclosed in a liquid-proof barrier, patients could one day have a sensor implanted under their skin that would not only detect when their levels were out of kilter but also signal to release insulin.
“Being able to have an enclosed waterproof system with its own power source would open up a lot of areas medically,” Hu said. “Right now, the focus is on being able to make the lines that form the circuit smaller.”
The process features “ink” made with silver nanowire, a bendable conductive material sometimes used for electronics in touch screens and liquid crystal displays. The nanowire is organized in tiny rods measured in nanometers, on par with the measurement scales for viruses and strands of DNA.
Although silver nanowire is commercially available, Hu and his team cut costs by developing their own ink formula that can be adjusted to exhibit different surface properties, such as a high resistance to water, depending on the application.
“We tried over thirty different kinds of paper, and by simply adjusting the viscosity or adhesiveness, the ink was able to handle different material surfaces,” Hu said.
The researchers also built their own programmed printing platform that uses a syringe infused with the silver nanowire ink to “write” a circuit design on the paper surface. To guide the syringe, an open source electronics control system called Arduino was implemented. The circuits were designed using CAD software.
“We use the syringe needle to deliver material to the surface while the substrate (paper) holds on to the 2-D platform,” Hu said. “We can design any kind of circuit structure, so the ink can write as many figures as we want.”
In an effort to make the manufacturing process both low-cost and rapid, the final step is—quite literally—a flash. The team sinters the ink to the paper using three flashes of light for just the right amount of heat.
To test the durability of the printed circuit, the paper is then rolled 5,000 times. “We rolled it until the paper was almost broken. The nanowire circuit had better mechanical properties than the paper fiber,” Hu said.
With patents in the works, Hu is reaching out to other UT researchers to experiment with different applications and substrates. “We’re working on printing on fabric or plastic,” Hu said. “While it’s good for many applications, paper won’t always work if the sensor gets wet.”
One of the early collaborators is Jayne Wu, associate professor of computer science and electrical engineering, who is developing a portable biosensor for virus detection.
“We think we can reduce her cost from a couple of dollars to a few cents per sensor,” Hu said.
Hu has also experimented with routing an antenna for communication applications, which could allow sensors to communicate with other devices. Once perfected, affordable proactive care sensors will be detecting minor health problems before they become major ones.