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Scientists develop ultra-thin battery that could be charged by tears

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The super-thin battery that could power smart contact lenses

Scientist Lee Seok Woo said a scene from a “Mission Impossible” movie inspired his latest invention: batteries for smart contact lenses.

In the fourth film of the series, an agent wears contact lenses capable of facial recognition and eye tracking. Lee wanted to make that lens a reality.

“I was thinking, ‘How can I work in this field of smart contact lenses?’” the Nanyang Technological University’s School of Electrical and Electronical Engineering associate professor told CNBC’s “The Edge.”

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Lee’s expertise in battery components served as the jumping off point for his foray into wearable technology. He realized smart contact lenses would need safe and compact batteries, which would be crucial for advancing development of these devices.

Contact lenses themselves are extremely thin, at 0.5 mm, thus the size and flexibility of these batteries are key to preventing user discomfort.

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“The thickness of our battery is about 0.2 mm, which is about twice the thickness of a human hair,” Lee said.

A demonstration of how a smart contact lens would fit on a human eye model.

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Lauren Choo | CNBC

Lee and his team invented a battery that can be powered using a biocompatible saline solution as an alternative to lithium-ion batteries, which contain flammable materials.

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This new battery can be charged using a conventional wire method, or a chemical method. The battery is coated with glucose and, when dipped into saline solution, the glucose will react with the sodium and chloride ions to charge it. 

Scientists at Singapore’s NTU demonstrate how the battery on a smart contact lens can be charged using the conventional wire method.

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Lauren Choo | CNBC

After eight hours of chemical charging, the battery can reach 80% of its full capacity. Then, it can be used for a couple of hours during the day.

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However, there is another unusual way to power the battery. 

“Tear solution also contains glucose. That means, while you’re wearing the contact lens, your tears can also charge the battery,” Lee said.

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“If you cry more, then you can charge your battery more.” 

A scientist showcase a smart contact lens fitted with a working prototype of a micro-battery.

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Lauren Choo | CNBC

Currently, the capacity and voltage of the battery is still very low. Using the two methods, the battery can only produce a voltage of approximately 0.3V – 0.6V. The standard voltage for one AA battery is 1.5V. 

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At this stage, that output is insufficient for powering data storage or internet connection, but the team is working to develop the battery’s specifications. 

A potential partner Lee has identified is in health care.

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“We use glucose as a biofuel. There are many diabetic patients who check their glucose level every day,” Lee said.

“We studied how we can detect glucose level while the user is wearing the contact lens.” 

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Despite the potential prospects of such an innovation, Lee thinks that costs should be kept low, considering the capacity of the batteries.

“Once it goes into very serious commercialization, the cost of the battery should only be a few dollars.”

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