The idea of “smart” contact lenses, which can monitor vital signs or levels of biomarkers indicative of disease, such as in glaucoma or glucose for diabetes, from the eyes, has been around for several years. However, the power requirements of previous technologies have made these systems less than ideal. For example, small devices need to be recharged frequently- a wired process that reduces mobility. Alternatively, inclusion of energy storage devices (i.e. batteries) make the final product bulky and typically heat up during operation. Now, a collaborative effort from universities in South Korea have shown, for the first time, the fabrication and successful operation of contact lenses with integrated energy storage and wireless charging devices, along with an LED (light) that can be used to report on some biological factor of interest.
The lens itself contains two functional layers stacked on top of each other. On the bottom layer, a “supercapacitor” is fabricated using a process called direct ink writing, in which mixtures of specific molecules allow for a solid component, like an electrode, to be drawn in a specific pattern directly onto the underlying layer. This capacitor functions as an energy storage device, like a small battery, and was designed so that the components are arc-shaped and only cover the iris, and thus do not interfere with the wearer’s vision. The top layer is the charging circuit which allows the supercapacitor to be wirelessly charged by placing a small antenna near the wearer’s eye (like a pair of glasses) during charging. The engineers described the fabrication of these devices into a single, functional contact lens, and tested various electrical and mechanical properties to ensure the device would not tear and would still function properly during operation. Finally, the functional units, including an LED located near the supercapacitor that turns on and off depending on if the device is charging or not, were tested on both a rabbit and a human. Neither subject showed signs of discomfort or irritation during the test.
While the results of the above study show the successful design and operation of a wirelessly chargeable contact lens, this is only the first of many steps into integrating such a design into functional, long-term smart contact lenses. One obvious limitation is the small trial pool- only one trial in one person is reported, and though the individual components were repeatedly tested to examine degradation in performance over time, this was not done for the final product itself. Additionally, though similar studies have reported the integration of a glucose sensor into smart contact lenses to test for high blood glucose in diabetics, the only functionality of the LED in this study is to report when the device is charging. Thus, proper sensor integration will also need to be demonstrated in this supercapacitor-based design. Finally, though the wireless charging is a step towards continuous operation, the antenna used for charging needs to be placed within 5 mm from the user’s eye, which may be undesirable for users who do not wish to wear glasses (as the antenna device itself bears a resemblance to a monocle or one lens in a pair of glasses) and can serve as another point of failure in the system should something happen to this charging device. If a single charge lasted for a long period of time, this could be only a small issue, but given that 45 seconds of charging is reported to only yield “over 60 seconds” of operation, it is difficult to judge how frequently recharging will be required.
Managing Correspondent: Andrew T. Sullivan
Press Articles: A contact lens that can show when blood glucose levels are high, Tech Xplore
Original Journal Article: “Printing of wirelessly rechargeable solid-state supercapacitors for soft, smart contact lenses with continuous operations,” Science Advances
Image Credit: Pixabay