Investigation of the antibacterial effects of silver nanolayers on the hard contact lenses coating after a two-year period

K. Koev, N. Donkov, H. Naidenski, T. Nurgaliev, L. Avramov
Institute of Electronics “Acad. Emil Djakov”, Bulgarian Academy of Sciences,
Bulgaria

Keywords: Ag/Al2O3 nanolayers, antibacterial action, hard contacts lenses coating, RF reactive magnetron sputtering, two-year period

Summary:

The investgation antibacterial properties of Ag-doped Al2O3 nanolayers deposited by RF reactive magnetron sputtering on hard contact lenses after a two-year period. The coatings were deposited on hard contact lenses by RF magnetron co-sputtering of Ag and Al under the following conditions: frequency 14 MHz; working pressure in the vacuum system ~ 5.5 Pa and the optimal mixture of Ar and O2. The study has been provoked by the need of suppressing the infections caused by pathogenic microorganisms following the placement of hard contact lenses. There is a risk of developing bacterial keratitisc and conjunctivitis when wearing contact lenses [1-2]. Although hard contact lenses are used less than soft, they are the best choice for some eye diseases lake a astigmatismus and Keratokonus. This has brought about the idea of forming protective coatings with antibacterial properties on the hard contact lenses. Further, the microbiological studies were conducted to establish the antibacterial action of the nanocomposite Ag/Al2O3 layers against Gram-positive and Gram-negative bacteria. The microbiological experiments was carried out to determine the antibacterial properties of the coating considered in suppressing Gram-positive and Gram-negative bacteria after a two-year period. The following strains were used: Staphylococcus aureus strain 29213 and Escherichia coli strain 35218 of the American Collection of Cell Cultures (ATCC); Pseudomonas aeruginosa strain 1390. The hard contact lenses were placed in 12-well polystyrene plates and covered by 800-µL suspension of the respective microorganisms in a concentration (colonies-forming units per mL) of 1×106 CFU/mL. The plates were shaken continuously and sampled at pre-defined intervals (0, 2, 5 and 24 hours) to determine the number of viable microorganisms. The latter was carried out by seeding ten-fold diluted solutions of the incubation mixtures in a nutrient medium (Tryptic soy agar, Oxoid) and counting the colonies-forming units (CFUs) after culturing for 24 hours at 37 oC. The strongest action of the layers was found against Pseudomonas aeruginosa - full inactivation after 2 hours; Escherichia coli - full inactivation after five hours; Staphylococcus aureus – full inactivation after twenty four hours. Our experimental findings suggest a very promising application of such antibacterial Ag/Al2O3 nanolayers regarding the reduction of eye infections when the hard contact lenses are used after a two-year period. The antimicrobial properties of the surface of Ag doped Al oxide coated products are very promising for many biomedical applications. Keywords: Ag/Al2O3 nanolayers, antibacterial action, hard contacts lenses coating, RF reactive magnetron sputtering, two-year period References 1.Stapleton F, Edwards K, Keay L, et al. Risk factors for moderate and severe microbial keratitis in daily wear contact lens users. Ophthalmology 2012;119:1516–21. 10.1016/j.ophtha.2012.01.052. 3. K. Koev, Donkov N., Stankova N., Moraliiski E., Najdenski Hr., Nurgaliev T., Zaharieva M., Avramov L. Application of Silver Antibacterial and Antifungal Nanolayers for Ocular Prostheses Coating, Phys. Status Solidi, Volume 216, Issue11, June 5, 2019, 1800695, https://onlinelibrary.wiley.com/journal/18626319, https://doi.org/10.1002/pssa.201800695 .