Scientists invent thin smart contact lenses battery charged by saline solution that could power smart contact lenses.

scientists invent micrometres-thin battery charged by saline solution that could power smart contact lenses.

NTU Singapore scientists invent micrometres-thin battery charged by saline solution that could power smart contact lenses

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Scientists from Nanyang Technological University, Singapore (NTU Singapore) have developed a flexible battery as thin as a human cornea, which stores electricity when it is immersed in saline solution, and which could one day power smart contact lenses.

thin smart contact lenses battery charged by saline solution

Smart contact lenses are high-tech contact lenses capable of displaying visible information on our corneas and can be used to access augmented reality. Current uses include helping to correct vision, monitoring wearers’ health, and flagging and treating diseases for people with chronic health conditions such as diabetes and glaucoma.

In the future, smart contact lenses could be developed to record and transmit everything a wearer sees and hears to cloud-based data storage. However, to reach this future potential a safe and suitable battery needs to be developed to power them. Existing rechargeable batteries rely on wires or induction coils that contain metal and are unsuitable for use in the human eye, as they are uncomfortable and present risks to the user.

The NTU-developed battery is made of biocompatible materials and 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, while the water the battery contains serves as the
‘wire’ or ‘circuitry’ for electricity to be generated.

The battery could also be powered by human tears as they contain sodium and
potassium ions, at a lower concentration. Testing the current battery with a simulated
tear solution, the researchers showed that the battery’s life would be extended an
additional hour for every twelve-hour wearing cycle it is used. The battery can also be
charged conventionally by an external power supply.

thin smart contact lenses battery charged by saline solution

Associate Professor Lee Seok Woo, from NTU’s School of Electrical and Electronic Engineering (EEE), who led the study, said: “This research began with a simple question: could contact lens batteries be recharged with our tears?

There were similar examples for self-charging batteries, such as those for wearable technology
that are powered by human perspiration. “However, previous techniques for lens batteries were not perfect as one side of the battery electrode was charged and the other was not.

Our approach can charge both electrodes of a battery through a unique combination of enzymatic reaction and selfreduction reaction. Besides the charging mechanism, it 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.”

Co-first author Dr Yun Jeonghun, a research fellow from NTU’s EEE said: “The
most common battery charging system for smart contact lenses requires metal
electrodes in the lens, which are harmful if they are exposed to the naked human eye.

Meanwhile, another mode of powering lenses, induction charging, requires a coil to be
in the lens to transmit power, much like wireless charging pad for a smartphone. 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

Highlighting the significance of the work done by the research team, NTU School of
Mechanical & Aerospace Engineering Associate Professor Murukeshan
Vadakke Matham, who specialises in biomedical and nanoscale optics and was not
involved in the study, said: “As this battery is based on glucose oxidase, which occurs
naturally in humans and powered by chloride and sodium ions, such as those in our
tears, they should be compatible and suitable for human usage.

Besides that, the smart contact lenses industry has been looking for a thin, biocompatible battery that does not contain heavy metals, and this invention could help further their development to meet some unmet needs of the industry.”

The research team has filed for a patent through NTUitive, NTU’s innovation and
enterprise company. They are also working towards commercialising their invention.
The findings were published in the scientific journal Nano Energy in June.

The team demonstrated their invention using a simulated human eye (see video). The
battery, which is about 0.5 millimetres-thin generates electrical power by reacting with
the basal tears – the constant tears that create a thin film over our eyeballs – for the
devices embedded within the lenses to function.

The flexible and flat battery discharges electricity through a process called reduction
when its glucose oxidase coating reacts with the sodium and chloride ions in the tears,
generating power and current within the contact lenses.

Thin smart contact lenses battery charged by saline solution

The team demonstrated that the battery could produce a current of 45 microamperes
and a maximum power of 201 microwatts, which would be sufficient to power a smart
contact lens.

thin smart contact lenses battery charged by saline solution

Laboratory tests showed that the battery could be charged and discharged up to 200
times. Typical lithium-ion batteries have a lifespan of 300 to 500 charging cycles.
The team recommends that the battery should be placed for at least eight hours in a
suitable solution that contains a high quantity of glucose, sodium and potassium ions,
to be charged while the user is asleep (see Figure 1).

Co-first author Miss Li Zongkang, a PhD student from NTU’s EEE said: “Although
wireless power transmission and supercapacitors supply high power, their integration
presents a significant challenge due to the limited amount of space in the lens.

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.
Furthermore, the electrodes placed at the outer side of the contact lens ensures that
the vision of the eye cannot be obstructed.”

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.

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