If It Doesn’t Fit, You Must Shrink It
Penn State’s shrinkable liquid-metal circuits create small, flexible, 3D wearables and smart devices that fit better and cost less.
The many capabilities of a wearable electronic device are of little use unless it can be made… well, wearable. Tracking health metrics can save lives, and keeping watch over physical performance has the potential to improve athletic skill. But none of this is possible if the wearable devices that collect this crucial information are left on a person’s nightstand.
The most important factors in making a wearable device usable are its size and conformability to the body. A device that is small and flexible can be transparently integrated into an individual’s daily routine. But a large, cumbersome device is likely to be seen as an annoyance; and an annoying wearable will only make it just so long before it gets tossed aside.
Bulky wearables may soon give way to practical and comfortable devices, thanks to the work of a group of researchers at Penn State University. They have developed a new fabrication technique that can produce small, flexible wearable electronics. These devices can mold themselves to each individual, and unlike past approaches, they can be manufactured at scale.
The key to this approach lies in combining liquid metal circuitry with a surprising material: the same heat-shrinkable polymer sheets used in children’s Shrinky Dinks toys. By printing circuits onto these inexpensive sheets and then shrinking them with controlled heating, the team can transform flat electronic patterns into compact, three-dimensional forms that contour to irregular surfaces, including the human body.
Traditional methods for producing flexible or 3D electronics have struggled with either complexity or cost. Techniques like 3D printing directly onto surfaces require specialized equipment and are difficult to scale, while approaches using stretchable materials often lack structural control or cannot easily be customized.
The new approach solves those challenges through a series of clever material innovations. Instead of rigid metals like gold or silver, the researchers turned to a gallium–indium liquid metal alloy known for its conductivity and fluidity. However, pure liquid metal droplets do not naturally adhere well to plastic surfaces and can break apart during shrinking. To address this, the team used ultrasonication and a detergent-like chemical to create a modified, partially solidified liquid metal composite that sticks securely to the polymer substrate. A plasma treatment of the plastic sheet further improved bonding.
Once the circuit is printed and the shrinking begins, the material folds and compresses into its final 3D configuration. This not only enhances mechanical durability but can also improve electrical performance. The researchers demonstrated compact antennas that self-adjust to household objects, enabling a low-cost path for retrofitting ordinary items into smart home devices.
As a proof of concept, the team also built a wearable ring embedded with a miniaturized accelerometer capable of transmitting gesture data over Wi-Fi. Early tests show promise for applications such as motion tracking or sign language interpretation. If this technology can prove itself in real-world applications, it could change wearables forever.