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"Smart" lenses hold commercial potential

Madison, Wis. - The human eye uses tiny muscles to focus on different distances. Man-made devices do the same by repositioning lenses, but some sensors do not require these external controls.

Researchers at the University of Wisconsin-Madison College of Engineering are investigating a liquid lens design that automatically adapts to environmental changes and could be used in a variety of commercial applications, including medical diagnostic tools and life science sensor arrays.

The millimeter-size lens utilizes a liquid droplet contained in a ring of hydrogel, a versatile polymer that can be chemically calibrated to contract and expand in response to a variety of stimuli such as temperature and acidity. As the conditions in the sensory system change, the hydrogel constricts or releases the droplet, causing it to change shape and focal length accordingly.

"When I was exposed to hydrogel, I was fascinated by what it could do," said Hongrui Jiang, assistant professor of electrical and computer engineering.

Jiang, in collaboration with colleagues David Beebe, professor of biomedical engineering, postdoctoral researcher Liang Dong, and doctoral student Abhishek Agarwal describe their work in a recent issue of the journal Nature.
Three-year wait

Almost immediately after being exposed to the hydrogel, Jiang began experimenting with applications of hydrogel actuation forces for sensor design, but "it was not as easy as I thought it would be," he said. "It took about three years to make it actually work."

Beebe's lab was instrumental in the project. It had already published research articles on stimuli responsive hydrogel structures as well as "pinned interfaces," a key component of the microfluidic system surrounding the lens. "The smart microlens technology integrates these two concepts," Beebe said.

"The final structure of the device was inspired by the human eye," Jiang added, noting that the hydrogel acts like the ciliary muscles that control the shape of the optic lens. "We have provided a very elegant way of getting optical output."

Because the device is both versatile and inexpensive to manufacture, the commercial applications are manifold. Researchers could use clusters of lenses to monitor all kinds of fluids, or manipulate the hydrogel to respond to other conditions such as the presence of proteins, salts, or electricity.

Grants from the UW-Madison Graduate School, the National Center for Food Protection and Defense at the University of Minnesota, and the Wisconsin Alumni Research Foundation (WARF) partially funded the research. The researchers are patenting the technology through WARF.

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