Electronic petals are created to fit around curved surfaces. After the backing is peeled off, the electronic components are cured on the surface using UV light. Image credit: Xingye Chen, Xue Feng, Ying Chen

Imagine a ball with an unidirectional sensor embedded in its leather hide, which could provide pitchers with every detail about their game. Consider a lens implanted with a microchip flexible enough to detect glucose levels in your eye so people with diabetes don’t need to poke their fingers.

These are only a few possibilities engineers are considering for flexible, curved electronics. However, there has yet to be a feasible method to mass produce. This could change thanks to the findings of a recently published paper published in Science Advances that describes a way of wrapping conventionally two-dimensional electronics that are mass-produced on planar, flat sheets wrapped around curved surfaces.

“This is just like wrapping a candy sweet,” says co-author Xue Feng, an engineer professor at Tsinghua University in Beijing, China. AAs he says, the wrapper is a 2D plane but can also change shape to fit an oblong candy.

The majority of wearable electronics in the world today — for instance, the processor chips inside Apple Watches are housed in silicon wafers with flat sides (see Wearable tech meets tattoo art in an attempt to change the world of both). The watch’s body is balanced. At the beginning of this research, co-author Ying Chen, an electrical engineer at the Institute of Flexible Electronics Technology of Tsinghua University at Zhejiang, attempted to bend and flex silicon chips to form an elongated surface. “But silicon is brittle and rigid and hard to deform,” Chen says. “It’s easy to fracture.”

Chen began to search for alternative options and found a math paper in 2009. The paper offered theoretical ideas on how to wrap a circular object on flat sheets and avoid wrinkles that could cause material waste. Based on the formulas in the paper, Chen and Feng employed geometric modeling to create the most efficient form for the 2D sheet that can quickly wrap around an arc. Instead of a rectangle similar to paper wrapped around balloons, they discovered that the most effective form is like flowers that are pressed with petals that can wrap around an object that is curving. As opposed to brittle silicon,, they employed stretchy elastomer semiconducting materials and metals.

The next concern was how to connect the flower petals to a curving object so that they would remain in the same place for the thousands of identical things made on a production line. “Alignment is important,” Chen says since it could ultimately impact the purpose of the product.

Initially, she was gently stretching petals onto round objects using her hands before peeling away the backing and applying UV light to fix the electronic components onto the curved surface. To make the process more efficient, two of them Feng created a soft press that uses a petals-shaped sheet; the round object is positioned in a tube approximately a centimeter wide, the width of an ordinary test tube. The balloon then expands into the line, putting even gentle pressure on the petals, ensuring they form a ring around the curving object.

Petals wrap around the circle more effectively than an ordinary rectangular sheet. Image credit: Xingye Chen, Xue Feng, Ying Chen

One of the most significant issues in making curvaceous sensors “is applying them to the object we care about,” says Tyler Ray, a professor of mechanical engineering at the University of Hawaii at Manoa. The authors came up with a “clever, elegant method,” he claims, that involves manufacturing sensors employing traditional 2D methods and affixing them to 3D objects. Ray says, however, that there are different ways to accomplish this feat, such as using 3D printing techniques instead of the transfer printing suggested in this article. However, the benefit of this approach, Ray argues, is that it relies on well-understood, well-controlled manufacturing methods, whereas 3D printing is more expensive and time-consuming per unit.

The biomedical engineer Philipp Gutruf thinks the adaptable approach and design guidelines offered by this paper are a valuable supplement to the existing literature. Gutruf has observed the general idea that involves wrapping 2D templates around 3D objects, which is demonstrated in earlier research papers, for instance, covering the heart inside the form of a wireless device for monitoring and control in mice. The scalable method here is a first, and the guidelines for designing spherical shapes may prove helpful, according to Gutruf, who works at the University of Arizona in Tucson. The extent to which this research can be applied to other complicated shapes required for biomedical devices is yet to be determined.