Researchers at Nanyang Technological University, Singapore (NTU Singapore) have invented an ultra-thin, flexible battery, comparable in thickness to the human cornea. This innovative battery stores energy when submerged in a saline solution, offering the potential to one day power smart contact lenses.
Smart contact lenses are advanced ocular devices with the capability to display visual information on the cornea. They have various applications, including vision correction, health monitoring, and assisting individuals with chronic conditions such as diabetes and glaucoma. In the future, these lenses might even have the capacity to record and transmit a wearer's visual and auditory experiences to cloud-based data storage.
However, achieving this future potential necessitates the development of a safe and suitable power source. Current rechargeable batteries rely on wires or metal-containing induction coils, which are impractical for use in the human eye due to discomfort and safety concerns.
The battery developed by NTU is crafted from biocompatible materials and does not incorporate any wires or harmful heavy metals typically found in lithium-ion batteries or wireless charging systems. It features a glucose-based coating that interacts with sodium and chloride ions present in the surrounding saline solution, with the water within the battery serving as the conduit for electricity generation.
Additionally, the battery has the potential to be energized by human tears, which contain sodium and potassium ions, albeit at lower concentrations. In tests conducted using a simulated tear solution, the research team demonstrated that the battery's lifespan could be extended by an extra hour for every twelve-hour usage cycle. Moreover, the battery remains capable of conventional charging via an external power supply.
Associate Professor Lee Seok Woo, from NTU’s School of Electrical and Electronic Engineering (EEE), who led the study, said: “This research began with 2 simple questions: could contact lens batteries be recharged with our tears? There were similar examples of 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 self-reduction 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 lenses.”
What sets this technology apart is its utilization of natural resources within the human body. The battery relies solely on glucose and water, both of which are safe for human use and environmentally friendly when disposed of. By harnessing these resources, the need for cumbersome external power sources and wiring connections can be eliminated.
While the smart contact lens powered by a tear-generated battery is not yet ready for widespread adoption, researchers are actively collaborating with contact lens companies to bring this innovative technology to market. Nonetheless, some limitations still require attention. The battery is currently capable of only 200 charge and discharge cycles, a constraint that needs to be addressed for prolonged use.
The NTU research team plans to conduct additional studies aimed at enhancing the battery's discharge capacity. Additionally, they are set to collaborate with multiple contact lens companies to integrate their innovative technology.
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