Imagine lenses that flash data on our corneas, keep an eye on our health, or flag diseases like glaucoma or diabetes

A new flexible battery as thin as a human eye’s cornea could power future smart-contact lenses, which in the future will be capable of displaying visible information on a eye’s cornea. It could be used to access augmented-reality devices, such as the Apple Vision Pro, for example.

Developed by researchers at Nanyang Technological University (NTU) in Singapore, the battery can be recharged simply by immersing it in saline solution. (Existing rechargeable batteries rely on wires or induction coils that contain metal so they are uncomfortable and present risks to the human eye.)

How they work

The new battery, made of biocompatible materials, does not contain wires or toxic heavy metals, such as those in lithium-ion batteries or wireless charging systems.

It has a glucose-based coating that reacts with the sodium and chloride ions in the saline solution surrounding it (water contained in the battery serves as the “wire” or “circuitry” for electricity to be generated).

Powered by tears

“This research began with a simple question: could contact lens batteries be recharged with our tears?” said Associate Professor Lee Seok Woo, from NTU’s School of Electrical and Electronic Engineering (EEE), who led the study. “Previous techniques for lens batteries were not perfect as one side of the battery electrode was charged and the other was not. The battery could be powered by human tears because they contain sodium and potassium ions, at a low concentration.

Testing the current battery with a simulated tear solution, the researchers showed that the battery’s life would be extended one additional hour for every 12-hour wearing cycle it is used. The battery can even be charged conventionally by an external power supply.

Takes just glucose and water to generate electricity

“Our approach can charge both electrodes of a battery through a unique combination of enzymatic reaction and self-reduction reaction. It also relies on just glucose and water to generate electricity, both of which are safe to humans and would be less harmful to the environment when disposed, compared to conventional batteries. The battery, which is about 0.5 millimetrers-thin, generates electrical power by reacting with the constant tears that create a thin film over our eyeballs.”

The NTU team will be conducting further research to improve the amount of electrical current their battery can discharge. They will also be working with several contact lenses companies to implement their technology.

Citation: Yun, J., Li, Z., Miao, X., Li, X., Lee, J. Y., Zhao, W., & Lee, S. W. (2023). Jeonghun Yun et al.  A tear-based battery charged by biofuel for smart contact lenses, Nano Energy, Jun 2023. DOI 1016/j.nanoen.2023.108344 (open-access)

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