A tear-based battery charged by biofuel for smart contact lenses

Smart contact lenses developed for medical and personal applications will require miniaturized power supplies, with integrated batteries providing promising options. However, charging batteries in small wearable devices is challenging because it is difficult to transfer electrical power through a miniaturized wired connection or wireless transmission unit. Herein, we develop safe, tear-based batteries integrated into contact lenses that are charged by biofuel during their storage. Enzymatic reactions of glucose oxidase and self-reduction of conducting polymer are utilized to charge the cathode and anode, respectively. The electrodes are embedded into a contact lens and discharged in an artificial tear solution followed by charging in a glucose solution via a bio-reaction (called bio-charging). The bio-charging battery shows a discharging capacity of 45 μA cm⁻² and a maximum power of 201 μW cm⁻², with its performance verified over 15 cycles. The bio-chargeable battery can also be charged conventionally by an external power supply.