Battery Powered by Tears for Smart Contact Lenses

Scientists at Singapore’s Nanyang Technological University have developed a flexible battery that is as thin as a human cornea.

I’ve written a lot about batteries in this column over the last few years. These batteries come in all shapes, sizes and chemistries. Mainly they are conventional batteries that we all know well and use in our everyday lives, only offering better performance, higher levels of safety, or in smaller packages. Occasionally they are very large batteries, especially those that uses molten salt and are designed to store renewable energy over longer periods of time. However, the battery in today’s column is pretty unique in that it is ultra-thin, flexible and designed for a specific application.

Wearables have become very popular in the recent past and that trend is set to continue as more applications become available. One of those applications is smart contact lenses, which are intended to provide benefits in a number of different ways. For example, health monitoring, where the smart lens can measure and display metrics such as glucose level and intraocular pressure. They could also be used to keep the user updated with other health information like heart-rate and calories burned during a work out. Finally, they could make augmented reality applications become more immersive, and with eye-tracking they could control HMI applications. In the future, it may even be possible for smart contact lenses to be used to correct the user’s vision, or to record everything that he/she sees and then transmit it to cloud storage.

The only drawback to smart contact lenses becoming reality is supplying them with power. Obviously mains electricity and even conventional batteries would be no use. Scientists from NTU Singapore have have attempted to tackle the problem by developing a flexible battery that is as thin as a human cornea, and can store electricity when it is immersed in saline solution. The development of the new battery was led by Associate Professor Lee Seok Woo from NTU’s School of Electrical and Electronic Engineering (EEE). There were a lot of challenges to developing the battery, including the fact that there were many materials that could not be used. For example, the metal wires that would normally be used for coils and connections would be uncomfortable and present a risk to the user.

The new battery from NTU is manufactured from biocompatible materials, with no wires or toxic heavy metals, like those found in Li-ion batteries or wireless charging systems. It features a glucose-based coating that was developed to react with the sodium and chloride ions in a saline solution surrounding it to recharge the battery. The water in the battery serves provides a catalyst to both assist in the movement of charge and to assist electricity to be generated.

In the future, the battery could be powered by human tears, as they also consist of sodium and potassium ions, however at lower concentrations. 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.

https://www.ntu.edu.sg/