image includes six photos of circuits printed on curved surfaces, including a contact lens

Engineering prints flexible circuits onto curved surfaces, from contact lenses to latex gloves

Researchers at North Carolina State University have demonstrated a new technique for printing electronic circuits directly onto curved and corrugated surfaces. The work paves the way for a variety of new soft electronic technologies, and researchers have used the technique to prototype “smart” contact lenses, pressure-sensitive latex gloves and transparent electrodes.

“There are many existing techniques for making printed electronics using different materials, but there are limitations,” says Yong Zhu, corresponding author of an article on the work. “One challenge is that existing techniques require the use of polymeric binders in the ‘ink’ you use to print the circuits. This will affect the conductivity of the circuit, requiring you to add an extra step to remove these binders after printing.

“A second challenge is that these printing techniques typically require you to print on flat surfaces, but many applications require surfaces that are not flat,” says Zhu, Andrew A. Adams Distinguished Professor of Mechanical and Aerospace Engineering at NC State.

“We have developed a technique that does not require binders and that allows us to print on a variety of curvilinear surfaces,” says Yuxuan Liu, first author of the publication and a graduate student at NC State. “We can also print the circuits as lattice structures with a uniform thickness.

The first step in the new technique is to create a template for the specific application that contains a specific pattern of microscale grooves. The stencil is then used to replicate this pattern in a thin elastic polymer film. The researchers then attach the thin polymer film to the respective substrate, which can be flat or curved. At this point, the tiny grooves in the polymer are filled with a liquid solution containing silver nanowires. The solution is allowed to dry at room temperature, leaving silver nanowires in a soft material with the desired shape and circuit pattern.

To demonstrate the technique, the researchers created three proof-of-concept prototypes. One of these was a “smart” contact lens with built-in circuitry that could measure the eye’s fluid pressure – relevant to some biomedical applications. One was a flexible, transparent electrode with circuits printed in a grid pattern that could be used in solar cells or on touch panels. The third is a latex glove with circuits printed on it that serve as pressure sensors and have applications in robotics and human-machine interface applications.

“We think this could be scaled up fairly easily in terms of manufacturing,” says Zhu. “We are open to discussions with industries interested in exploring the potential of this technology.”

The publication “Curvilinear Soft Electronics by Micromolding of Metal Nanowires in Capillaries” has appeared in the Open Access Journal scientific advances. The paper was co-authored by Brendan O’Connor, a professor of mechanical and aerospace engineering at NC State; Jingyan Dong, Professor in the Edward P. Fitts Department of Industrial and Systems Engineering, NC; and Michael Zheng, a graduate student at NC State.

The work was carried out with support from the National Science Foundation under grants 1728370 and 2134664.

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Note to the editor: The abstract study follows.

“Curvilinear soft electronics by microshaping metal nanowires in capillaries”

authors: Yuxuan Liu, Michael Zheng, Brendan O’Connor, Jingyan Dong and Yong Zhu, North Carolina State University

Released: Nov 18, scientific advances

DOI’s: 10.1126/sciadv.add6996

Abstract: Metal nanowire soft electronics have attracted a lot of attention due to their high electrical conductivity and mechanical flexibility. However, the high-resolution, complex patterning of metal nanowires on curvilinear substrates remains a challenge. Here, a microshaping-based method for scalable metal nanowire printing is reported, enabling complex and highly conductive patterns on soft, curvilinear, and uneven substrates with high resolution and uniformity. Print resolution of 20 μm and conductivity of printed patterns of ~6.3×106 S/m can be achieved. Printing lattice structures with uniform thickness for transparent conductive electrodes (TCEs) and printing pressure sensors directly onto curved surfaces such as gloves and contact lenses are also realized. The printed hybrid soft TCEs and smart contact lenses show promising applications in optoelectronic devices and personal health monitoring, respectively. This printing process can be extended to other nanomaterials for large area printing of high-performance soft electronics.


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