Microbial keratitis is one of the most serious potential complications for contact lens wearers. It’s an infection of the cornea that is caused by bacteria; the most common being Pseudomonas aeruginosa.

Previous studies have found that existing disinfecting solutions are not effective for preventing biofilm, which are clusters of bacteria that attach to the surface of lenses.

Hydroquinine, an organic compound found in the bark of some trees, is known to have bacterial killing activity against Pseudomonas aeruginosa and several other clinically important germs, including Staphylococcus aureus, Escherichia coli, and Klebsiella pneumoniae.

The team behind the discovery, from the University of Portsmouth in England and Naresuan and Pibulsongkram Rajabhat universities in Thailand, has now explored the potential use of multipurpose formulas containing hydroquinine as a disinfectant for contact lenses.

They examined the antibacterial, anti-adhesion, and anti-biofilm properties of hydroquinine-formulated multi-purpose solutions (MPSs), and then compared it to two commercial MPSs; Opti-free Replenish and Q-eye. The natural compound killed 99.9 per cent of bacteria at the time of disinfection.

The paper, published in Antibiotics, says these findings may aid in the development of novel disinfectants aimed at combating the P. aeruginosa bacteria.

Dr Robert Baldock from the School of Pharmacy and Biomedical Sciences at the University of Portsmouth, said: “Commercially available disinfecting solutions, which are made up of a number of chemicals, can sometimes cause reactions with painful side-effects.

“We hoped to demonstrate that new agents made from natural products may be an excellent option to limit or reduce the risk of contact lens contamination.

“It is exciting to see how this research has progressed; from discovery to exploring potential applications.”

There are up to 3.5 million reports of corneal infections annually, and in extreme cases it can result in permanent eye damage and vision loss. The risk of microbial keratitis doubles when someone wears contact lenses overnight and or longer than the recommended daily amount.

Corneal blindness resulting from microbial keratitis is emerging as a prominent cause of visual disability, according to the World Health Organisation (WHO). The World Health Organisation (WHO) has also classified multidrug-resistant P. aeruginosa as one of the most concerning pathogens.

Drug-resistant bacteria occur in more than 2.8 million infections and are responsible for 35,000 deaths per year. Antimicrobial resistance happens when germs change over time and no longer respond to medicines, making it difficult to treat infections.

Amoxicillin and Trimethoprim are commonly prescribed antibiotics that certain strains of P. aeruginosa have become resistant to.

Hydroquinine is already known to be an effective agent against malaria in humans, and it is also being used in the Netherlands to treat nocturnal muscle cramps. Until now, there has been little investigation into its drug-resistant properties.

Lead author, Sattaporn Weawsiangsang from the Faculty Of Allied Health Sciences at Naresuan University, is currently a visiting researcher at the University of Portsmouth.

She said: “Our initial findings suggest that soaking contact lenses in a multi-purpose solution containing hydroquinine is possibly helpful to prevent contamination and infection.

“However, further investigation is needed to determine whether hydroquinine itself also has  adverse reactions or toxicity.

“We are continuing to test the compound on a number of cells, and so far, the results are really promising. This potential development could contribute to the creation of new disinfectants from natural products, effectively combating P. aeruginosa infections and reducing cases of corneal infections.”

The paper concludes by recommending further research examining the effectiveness of hydroquinine with several different contact lens materials, and against other pathogenic microorganisms.

A smart contact lens is a product attached to the human eye like a normal lens and provides various information. Research on the lens is being conducted mainly on diagnosing and treating health. Recently, Google and others are developing smart contact lenses for displays that can implement AR. Still, many obstacles to commercialization exist due to severe technical challenges.

In implementing AR with smart contact lenses, electrochromic¹⁾ displays that can be driven with low power are suitable, and “Pure Prussian Blue” color, with high price competitiveness and quick contrast and transition between colors, is attracting attention as the lens’ material. However, in the past, the color was coated on the substrate in the form of a film using the electric plating method²⁾, which limited the production of advanced displays that can express various information (letters, numbers, images).”

The achievement of KERI-UNIST lies in the fact that it is a technology that can realize AR by printing micro-patterns on a lens display using a 3D printer without applying voltage. The key is the Meniscus of used ink. The Meniscus is a phenomenon in which a curved surface is formed on the outer wall without water droplets bursting due to capillary action when water droplets are gently pressed or pulled with a certain pressure.

Prussian blue is crystallized through solvent evaporation in the Meniscus formed between the micronozzle and the substrate. The meniscus of the acidic-ferric-ferricyanide ink is formed on the substrate when the ink-filled micronozzle and substrate come in contact. Heterogeneous crystallization of FeFe(CN)6 occurs on the substrate within the meniscus via spontaneous reactions of the precursor ions (Fe3+ and Fe(CN)3−) at room temperature. Simultaneously, the solvent evaporation is occurred at the meniscus surface. When water evaporates from the meniscus, the water molecules and precursor ions move toward the meniscus surface by convective flow, generating a preferential accumulation of the precursor ions in the outer part of the meniscus. This phenomenon induces the edge-enhanced crystallization of FeFe(CN)6; this is crucial for controlling the factors that influence the crystallization of FeFe(CN)6 in the printing step to obtain uniformly printed PB patterns on a substrate. As with conventional electroplating, the substrate used to have to be a conductor when voltage was applied, but a great advantage of using the meniscus phenomenon is that there is no restriction on the substrate that can be used because crystallization occurs by natural evaporation of the solvent.

Through the precise movement of the nozzle, the crystallization of Prussian blue is continuously performed, thereby forming micro-patterns. Patterns can be formed not only on flat surfaces but also on curved surfaces. The research team’s micro-pattern technology is very fine (7.2 micrometers) that can be applied to smart contact lens displays for AR, and the color is continuous and uniform.

The main expected application area is navigation. Simply by wearing a lens, navigation unfolds in front of a person’s eyes through AR. Games such as the popular “Pokemon Go” can also be enjoyed with smart contact lenses, not smartphones.

Dr. Seol Seung-Kwon’s of KERI said, “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.” He added, “It will greatly contribute to the miniaturization and versatility of AR devices.”

The related research results were recently published as a cover articler in Advanced Science (IF 17.521/JCR 4.71%), a world-renowned academic journal in the field of materials science, in recognition of its excellence.

The research team believes that this achievement will attract a lot of attention from companies related to batteries and biosensors that require micro-patterning of Prussian blue as well as the AR field, and plans to find related demand companies and promote technology transfer.

Meanwhile, KERI is a government-funded research institute under the Ministry of Science and ICT’s National Research Council for Science and Technology. Dr. Seol Seung-Kwon is also a professor at the KERI campus of the University of Science and Technology (UST). <KERI>

1) Electrochromism: a phenomenon where the color of a substance changes reversibly due to an electrochemical reaction.

2) Plating is the process of applying a thin layer of another metal to improve the surface condition of an object. In this process, if electrical energy is used, it is called “electroplating,” and if chemical reactions are utilized without electricity, it is referred to as “electroless plating.” Particularly electroplating is mainly used in the production of jewelry such as rings.