Cry me a current

Singapore scientists developed a flexible battery as thin as a human cornea which stores electricity when immersed in saline solution and could one day power smart contact lenses (CLs).

The battery’s development was led by Associate Professor Lee Seok Woo from the School of Electrical and Electronic Engineering at Nanyang Technological University (NTU).

Smart CLs can display visible information on the wearer’s corneas to access augmented reality, scientists explained. Current uses include vision correction, monitoring the wearer's health and flagging and treating people with chronic health conditions such as diabetes and glaucoma. In the future, smart CLs could be developed to record and transmit everything a wearer sees and hears to cloud-based data storage.

However, to achieve their potential, a safe and suitable battery needs to be developed to power the CLs. Existing rechargeable batteries rely on wires or induction coils containing metal, making them uncomfortable and posing health risks.

The NTU-developed battery is made of biocompatible materials without wires or toxic heavy metals, such as those in lithium-ion batteries or wireless charging systems. Its glucose-based coating reacts with the sodium and chloride ions in the saline solution surrounding it, while the water the battery serves as the ‘circuitry’ for electricity to be generated.

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