Wearable electronics could be more wearable, according to a research team at Penn State.
The researchers developed a scalable, versatile approach to designing and fabricating wireless, internet-enabled electronic systems that can better adapt to 3D surfaces, like the human body or common household items, paving the path for more precise health monitoring or household automation, such as a smart recliner that can monitor and correct poor sitting habits to improve circulation and prevent long-term problems.
The method, detailed in Science Advances, involves printing liquid metal patterns onto heat-shrinkable polymer substrates - otherwise known as the common childhood craft "Shrinky Dinks." According to team lead Huanyu "Larry" Cheng, James L. Henderson, Jr. Memorial Associate Professor of Engineering Science and Mechanics in the College of Engineering, the potentially low-cost way to create customizable, shape-conforming electronics that can connect to the internet could make the broad applications of such devices more accessible.
"We see significant potential for this approach in biomedical uses or wearable technologies," Cheng said, noting that the field is projected to reach $186.14 billion by 2030. "However, one significant barrier for the sector is finding a way to manufacture an easy-to-customize device that can be applied to freestanding, freeform surfaces and communicate wirelessly. Our method solves that."
Yangbo Yuan, a graduate student in engineering science and mechanics and co-author on the study, explained that current production methods for wearable, internet-connected electronics include directly fabricating circuits onto target surfaces via 3D printing, a complex process that limits scalability and cost-effectiveness. He said that more cost-effective methods that use liquid metal and manipulating softened thermoplastic materials offer limited reconfiguration or customization due to the need for pre-conforming molds. Overall, no current commercial method solves the need for applying a smart, Wi-Fi-enabled device onto complex 3D surfaces or structures at scale.
"We've been working on approaches to get this circuit onto the human body or different 3D geometries, but the dream is always to find a solution that is super easy to fabricate, not just in a specialized lab, but also at home," Cheng said.
The researchers' dream came true, Cheng said, when they discovered the polymer used in shrink plastic craft kits, a commonly used children's craft material used to create custom-cut items like keychains or jewelry. Packages of sheets can be bought online for under $15, so the sheets met their low-cost, readily available criteria.
"When we saw this shrinkable craft, it seemed like the perfect fit," Yuan said, explaining that when heated, the sheets shrink uniformly in the horizontal and vertical directions, allowing for a controlled shrinking process. "Our purpose is really to create a framework that is DIY and widely available to as many people as possible."
With a substrate material selected, the researchers needed to determine a way to apply a circuit to the polymer that would withstand the heat-shrinking process without losing conductivity or structural integrity. Conductivity is key to minimizing power consumption and increasing data transmission efficiency, which is integral for connecting the circuit to a Wi-Fi network, the researchers said.
