Advancements in Ophthalmic Technology: Ultra-Thin Battery Powered by Saline Solution Engineered by Scientists

Associate Professor Lee Seok Woo, part of the faculty at the School of Electrical and Electronic Engineering (EEE) at Nanyang Technological University (NTU) Singapore, displays a groundbreaking flexible battery, comparable in thinness to the human cornea.

A team of researchers from Nanyang Technological University in Singapore (NTU Singapore) has engineered an innovative energy storage device that is as thin as a human cornea and charges itself when immersed in a saline solution. This technological breakthrough has the capability to energize the next generation of smart contact lenses.

Smart contact lenses are advanced optical devices capable of projecting visual data directly onto the human cornea, providing potential applications in augmented reality. These lenses have existing functionalities, ranging from vision correction to the continuous health monitoring of individuals with chronic conditions like diabetes and glaucoma. Future iterations may even possess the ability to record and upload visual and auditory data to cloud storage.

To achieve such advancements, a safe and suitable power source is necessary. Traditional rechargeable batteries, which rely on wired or inductive systems featuring metal components, are not feasible for ocular use due to their discomfort and potential hazards.

The flexible battery developed by NTU is fabricated from biocompatible materials and eschews the use of wires and hazardous heavy metals commonly found in lithium-ion batteries or wireless charging systems. It employs a glucose-based coating that interacts with sodium and chloride ions in the surrounding saline solution. The battery’s internal water content serves as the electrical pathway for the generation of electricity.

Additionally, the battery can be powered by human tears, which have a lower concentration of sodium and potassium ions. Experiments using a synthetic tear solution revealed that the battery’s lifespan could be extended by an extra hour per twelve-hour usage cycle. Traditional external power supplies can also be employed to charge the battery.

Associate Professor Lee Seok Woo, the study’s lead investigator from NTU’s EEE, stated that the idea for the battery originated from the question of whether tear-based recharging could be possible. While earlier technologies existed for self-charging batteries like those powered by human sweat, the present technology offers advantages by charging both battery electrodes through a unique blend of enzymatic and self-reduction reactions. Furthermore, the energy generation relies solely on glucose and water, making it human-safe and environmentally benign when disposed of.

Dr. Yun Jeonghun, a research fellow from NTU’s EEE and co-first author of the study, elaborated on the drawbacks of conventional charging systems that involve metal electrodes or induction coils, posing safety risks and design limitations. The tear-powered battery overcomes these challenges while leaving room for further advancements in smart contact lens technology.

Uninvolved in the study but commenting on its significance, Associate Professor Murukeshan Vadakke Matham from NTU School of Mechanical & Aerospace Engineering, an expert in biomedical and nanoscale optics, endorsed the biocompatibility and suitability of the battery for human use. He added that this invention fills a gap in the smart contact lens industry, which has been searching for a safe, ultra-thin and biocompatible battery.

The researchers have applied for a patent via NTUitive, NTU’s commercialization arm, and are in the process of bringing their invention to market.

The research findings have been recently published in the scientific journal Nano Energy.

Electrochemical Reactions from Human Tears

The NTU team demonstrated the battery’s capabilities through simulations using a human eye model. Measuring approximately 0.5 millimeters in thickness, the battery generates electrical energy by reacting with basal tears. These constant tears form a thin layer over our eyes, allowing embedded devices within the lenses to operate.

The battery achieves electrical output through a process known as reduction, facilitated by a glucose oxidase coating that reacts with the ions present in tears, generating sufficient energy to power a smart contact lens.

Laboratory evaluations indicated that the battery could undergo up to 200 charge and discharge cycles, compared to the 300 to 500 cycles typical of lithium-ion batteries.

For optimal charging, the team suggests immersing the battery for at least eight hours in a solution rich in glucose, sodium, and potassium ions, ideally while the wearer is sleeping.

Miss Li Zongkang, a PhD student from NTU’s EEE and co-first author of the study, noted that while wireless power transmission and supercapacitors provide high power, their integration poses challenges due to limited space within the lens. By incorporating the battery and biofuel cell as a single unit, the need for additional wired or wireless components is eliminated. Furthermore, the electrodes are positioned on the exterior of the contact lens to avoid vision obstruction.

Ongoing research aims to enhance the electrical output of the NTU-developed battery, and collaborations with contact lens companies for technology implementation are in progress.

Reference: “A tear-based battery charged by biofuel for smart contact lenses” authored by Jeonghun Yun, Zongkang Li, Xinwen Miao, Xiaoya Li, Jae Yoon Lee, Wenting Zhao, and Seok Woo Lee, was published on 13 March 2023 in Nano Energy. DOI: 10.1016/j.nanoen.2023.108344

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