An Emotionally Charged Battery

The nascent field of smart contact lenses seems to be on the brink of transforming how we interact with both technology and the world around us. These devices seek to merge cutting-edge electronics with the convenience of wearable eyewear, creating a seamless integration between the digital realm and our everyday lives. They hold the potential to reshape various aspects of our routine activities, from healthcare to communication, entertainment, and beyond.

At their core, smart contact lenses are designed to provide a direct interface between the human visual system and digital information. Equipped with microelectronics, sensors, and even minuscule displays, these lenses can overlay augmented reality content onto the wearer's natural field of vision. This opens up a plethora of applications ranging from real-time navigation and hands-free information retrieval to immersive gaming experiences. Imagine strolling through a city while receiving turn-by-turn directions directly in your line of sight or effortlessly browsing your emails without needing to glance at a screen.

While the possibilities are exciting, the development of smart contact lenses also poses significant challenges. Miniaturizing electronics while ensuring comfort, breathability, and safety for the wearer is a complex feat. Powering these devices in an unobtrusive manner, handling data privacy and security concerns, and complying with regulatory standards are among the hurdles that researchers and engineers in this field must overcome.

Supplying power is particularly fraught with difficulties, as any solution must not only be tiny and deliver sufficient energy, but it must also be safe — it will be sitting directly on top of people’s corneas after all. It is this challenge that a group of scientists at Nanyang Technological University have decided to tackle. They have developed a new type of battery that is only a few micrometers in thickness, yet it can supply enough energy to keep a low-power device in operation. And since these batteries are recharged when immersed in a saline solution, all you need to do to keep them going is spend a few minutes watching Old Yeller or It’s a Wonderful Life.

At present, existing power storage and delivery solutions are not very promising for smart contact lenses. Traditional batteries contain dangerous materials like organic solvents and concentrated salts that would cause severe eye damage in the event of a leak, not to mention the unfortunate tendency of certain types of high energy density batteries to catch fire. Inductive power transmission is another option that would perhaps be safer, but does require the inclusion of an induction coil in the contact lens, and also necessitates the device remaining impractically close to the transmitter for normal use.

The researchers’ device does away with toxic chemicals, wires, and induction coils in favor of a biocompatible biofuel cell that generates electricity from enzymatic reactions with normal biological fluids. By leveraging a glucose-based coating and conductive polymer that react with the sodium and chloride ions naturally present in tears, it was demonstrated that energy could be generated. The prototype did not produce a lot of energy, with a maximum discharging capacity of 45 μA per square centimeter, but that could be just enough for certain low-power devices. And of course, the capacity could increase in the future, while the power draw of electronic components simultaneously decreases.

These batteries are still under development, but one day they could safely supply power to smart contact lenses that monitor the wearer’s health, tracking conditions like diabetes and glaucoma. Further down the road, they might power the transparent augmented reality devices that finally get people to stop staring at their phones all day long.