Saline-charged battery for smart contact lenses

9th November 2023
Sheryl Miles

Scientists at Nanyang Technological University, Singapore (NTU Singapore) have created a flexible battery, as thin as the human cornea, which draws power from saline solution.

This is a breakthrough that has the potential energise smart contact lenses in the future.

Innovative power for smart lenses

Smart contact lenses, equipped to display information directly onto the cornea, offer capabilities for augmented reality access, health monitoring, and potentially, in the future, the recording and transmission of visual and auditory data to cloud storage.

However, powering these devices safely and effectively remains a challenge, as traditional rechargeable batteries with metal components are not suitable for eye wear due to discomfort and risk to the user.

The newly developed battery by NTU is free from wires and toxic metals and is made from biocompatible materials. It harnesses a glucose-based coating that reacts with the sodium and chloride ions in saline solution, which acts as a conductor for electricity generation.

A potential tear-powered source

Interestingly, human tears, containing sodium and potassium ions, could also serve as a power source for the battery. Tests with a simulated tear solution have shown that the battery life could be extended by an hour for every twelve hours of use. Additionally, it can be conventionally charged using an external power source.

Associate Professor Lee Seok Woo from NTU's School of Electrical and Electronic Engineering, who led the study, shared: "This research began with a simple question: could contact lens batteries be recharged with our tears? … Our approach can charge both electrodes of a battery through a unique combination of enzymatic reaction and self-reduction reaction."

Co-first author Dr Yun Jeonghun, a research fellow from NTU's EEE, highlighted the advantages of the new system: "The most common battery charging system for smart contact lenses requires metal electrodes in the lens ... Our tear-based battery eliminates the two potential concerns that these two methods pose, while also freeing up space for further innovation in the development smart contact lenses."

Expert endorsement

The significance of this research is underscored by Associate Professor Murukeshan Vadakke Matham from NTU's School of Mechanical and Aerospace Engineering: "As this battery is based on glucose oxidase ... they should be compatible and suitable for human usage."

The research team has filed a patent through NTUitive, NTU's innovation and enterprise company, and is exploring commercial avenues for their invention.

Research publication and potential

The findings were published in Nano Energy in June. The team showcased the battery using a simulated human eye model. The battery produced a current of 45 microamperes and a power output of 201 microwatts in laboratory tests, enough to potentially power smart lenses. With up to 200 charge-discharge cycles, its longevity competes with typical lithium-ion batteries.

Co-first author Miss Li Zongkang, a PhD student from NTU's EEE, explained the design's efficiency: "By combining the battery and biofuel cell into a single component, the battery can charge itself without the need for additional space for wired or wireless components."

The NTU team is continuing research to enhance the battery's electrical output and is in talks with contact lens manufacturers to integrate their technology.

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