According to the researchers, from Ulsan National Institute of Science and Technology (UNIST) and the Korea Electrotechnology Research Institute (KERI), the new smart contact lenses can be worn inside the eye like a normal lens and could be used to enhance convenience and productivity in everyday life.
Published in Advanced Science, the work has been jointly led by UNIST Department of Mechanical Engineering’s Professor Im Doo Jung, and Dr. Seung Kwon Seol from the Smart 3D Printing Research Team at KERI.
Some of the disadvantages of existing AR devices include high price, experimental technology and bulky appearance. On the other hand, the team said that smart contact lenses can be affordable and convenient. Whilst leading companies are working on creating smart contact lenses capable of implementing AR, barriers to commercialisation exist due to severe technical challenges, researchers explained.
According to the team, energy-saving electrochromic (EC) displays that can be driven with low power are suitable for implementing AR with smart contact lenses.
Prussian blue (PB) has been regarded as an attractive EC material due to its uniform colouration, fast kinetics, high optical contrast, multiple colour states (blue, white, green), environmental friendliness, and cost competitiveness.
However, this has limitations in displaying words or images that are needed for a display on AR smart contact lenses because of the difficulty of micro-patterning PB on the contact lens, the team noted.
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The team said they developed a ‘simple and effective’ printing strategy to produce micro-patterns of PB using the meniscus-guided printing of an acidic-ferric-ferricyanide ink composed of FeCl3, K3Fe(CN)6, and HCl. The key to this is the meniscus of the acidic-ferric-ferricyanide ink.
As with a conventional electroplating approach, the substrate used must be a conductor when voltage is applied. However, the team explained, with the meniscus phenomenon, there is no restriction on the substrate that can be used because crystallisation occurs by natural evaporation of the solvent.
Researchers reported that the micro-pattern technology is very fine (7.2 micrometres) and can be applied to smart contact lens displays for AR, and the colour is continuous and uniform.
Through experiments, researchers reported successful demonstration of PB-based EC displays in a smart contact lens with a navigation function. The team confirmed the device was able to display directions to the destination to the user on the EC display by receiving GPS coordinates in real time.
“Although thin glass ITO was used for the EC display in this study, it can be further developed as a method of patterning transparent electrodes, such as graphene on flexible materials and printing EC materials," the team stated.
"We believe that our novel strategy will serve as an attractive method for realizing PB-based EC displays as well as diverse functional devices with micro PB patterns."
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