Scientists from Nanyang Technological University, Singapore (NTU Singapore) have made a breakthrough in the development of smart contact lenses by creating a flexible battery as thin as a human cornea. This battery can store electricity when immersed in a saline solution, potentially powering future smart contact lenses.
Smart contact lenses are advanced lenses capable of displaying visible information on our corneas, enabling augmented reality experiences. They currently have various uses, including vision correction, health monitoring, and disease detection and treatment for individuals with chronic conditions like diabetes and glaucoma. In the future, smart contact lenses could even record and transmit everything a wearer sees and hears to cloud-based data storage.
However, to unlock this potential, a safe and suitable battery must be developed to power these lenses. Existing rechargeable batteries rely on wires or induction coils that contain metal, making them uncomfortable and risky for use in the human eye.
The battery developed by NTU is made of biocompatible materials and does not contain wires or toxic heavy metals found in lithium-ion batteries or wireless charging systems. It has a glucose-based coating that reacts with the sodium and chloride ions in the surrounding saline solution. The water within the battery serves as the “wire” or “circuitry” for generating electricity.
Interestingly, the battery can also be powered by human tears, which contain sodium and potassium ions at a lower concentration. Testing the battery with a simulated tear solution, researchers found that its lifespan could be extended by an additional hour for every twelve-hour wearing cycle. Additionally, the battery can be conventionally charged using an external power supply.
Associate Professor Lee Seok Woo from NTU’s School of Electrical and Electronic Engineering led the study. He explained that their approach charges both electrodes of the battery through a unique combination of enzymatic reaction and self-reduction reaction. The battery relies on glucose and water to generate electricity, which are safe for humans and less harmful to the environment when disposed of compared to conventional batteries.
Dr. Yun Jeonghun, a research fellow from NTU’s School of Electrical and Electronic Engineering, highlighted the drawbacks of current battery charging systems for smart contact lenses. These systems either require metal electrodes in the lens, which can harm the naked human eye, or induction charging, which necessitates a coil within the lens to transmit power. The tear-based battery developed by NTU eliminates these concerns and allows for further innovation in smart contact lens development.
The research team has filed for a patent through NTUitive, NTU’s innovation and enterprise company, and is working towards commercializing their invention. Their findings were published in the scientific journal Nano Energy in June.
The team demonstrated their invention using a simulated human eye. The battery, which is about 0.5 millimeters thin, generates electrical power by reacting with the basal tears that create a thin film over our eyeballs. The battery discharges electricity through a process called reduction when its glucose oxidase coating reacts with the sodium and chloride ions in the tears.
Laboratory tests showed that the battery could be charged and discharged up to 200 times, while typical lithium-ion batteries have a lifespan of 300 to 500 charging cycles. The team recommends placing the battery in a suitable solution containing high quantities of glucose, sodium, and potassium ions for at least eight hours to charge while the user sleeps.
Miss Li Zongkang, a PhD student from NTU’s School of Electrical and Electronic Engineering, emphasized the advantages of combining the battery and biofuel cell into a single component. This integration allows the battery to charge itself without requiring additional space for wired or wireless components. The electrodes placed on the outer side of the contact lens ensure that vision is not obstructed.
The NTU team plans to conduct further research to enhance the amount of electrical current their battery can discharge. They will also collaborate with contact lens companies to implement their technology.
Overall, this breakthrough in battery technology brings us one step closer to the future of smart contact lenses, offering exciting possibilities for augmented reality and healthcare applications.