Scientists develop AR-based navigated contact lenses using 3D printing

Why is it Prussian blue?

Electrochromic screens that can be controlled with little power and the color "Pure Prussian Blue" are suited for implementing augmented reality with smart contact lenses.

As the solvent evaporates, Prussian blue crystallizes in the Meniscus that forms between the micronozzle and the substrate, when the ink-filled micronozzle and substrate make contact, an acidic-ferric-ferricyanide ink meniscus forms on the substrate.

At normal temperatures, spontaneous interactions between the precursor ions, Fe3+ and Fe(CN)3, cause heterogeneous crystallization of FeFe(CN)6 to form on the substrate within the meniscus.

Prussian blue crystallization is continuously carried out through the exact movement of the nozzle, resulting in the formation of micro-patterns. Not just flat surfaces but also curved surfaces can generate patterns. The micro-pattern technology developed by the study team is extremely fine (7.2 micrometers) and can be used to create smart contact lens displays for augmented reality.

"Our achievement is a development of 3D printing technology that can print functional micro-patterns on non-planner substrate that can commercialize advanced smart contact lenses to implement AR," said Dr. Seol Seung-Kwon. "It will greatly contribute to the miniaturization and versatility of AR devices," he added.

The study team plans to discover associated demand companies and foster knowledge transfer because they expect this accomplishment to draw significant attention from businesses involved in batteries and biosensors, which both require micro-patterning of Prussian blue.

The study was published in Advanced Science on November 28, 2022.

Study abstract:

Using energy-saving electrochromic (EC) displays in smart devices for augmented reality makes cost-effective, easily producible, and efficiently operable devices for specific applications possible. Prussian blue (PB) is a metal-organic coordinated compound with unique EC properties that limit EC display applications due to the difficulty in PB micro-patterning. This work presents a novel micro-printing strategy for PB patterns using localized crystallization of FeFe(CN)6 on a substrate confined by the acidic-ferric-ferricyanide ink meniscus, followed by thermal reduction at 120 °C, thereby forming PB. Uniform PB patterns can be obtained by manipulating printing parameters, such as the concentration of FeCl3·K3Fe(CN)6, printing speed, and pipette inner diameter. Using a 0.1 M KCl (pH 4) electrolyte, the printed PB pattern is consistently and reversibly converted to Prussian white (CV potential range: −0.2–0.5 V) with 200 CV cycles. The PB-based EC display with a navigation function integrated into a smart contact lens is able to display directions to a destination to a user by receiving GPS coordinates in real time. This facile method for forming PB micro-patterns could be used for advanced EC displays and various functional devices.