Development of antibacterial contact lenses containing metallic nanoparticles

Abstract

Abstract Background Contact lens wear can result in adverse events including bacterially-driven corneal infection and inflammation. These are the result of various kinds of bacteria adhering to contact lenses and either initiating infection of the cornea or producing inflammation of the cornea and conjunctiva. In order to reduce the incidence of these events antimicrobial contact lenses are being developed. In this study, antimicrobial contact lenses containing nanoparticles of silver or copper, or a combination of the two, were produced and evaluated. Methods Silver and copper nanoparticles were produced in polyvinyl alcohol (PVA) polymers by incorporating salts of these metals and then reducing the salts to nanoparticles with sodium hydroxide. Incorporation of nanoparticles into the PVA was confirmed using transmission electron microscopy, attenuated total reflection (ATR) spectroscopy and X-ray photoelectron spectroscopy (XPS). The nanoparticle-containing polymers were then evaluated for physical characteristics such as tensile strength, water content and coloration. PVA containing polymers were evaluated for cytotoxicity to mammalian cells using a standard assay, and for antimicrobial activity using three different assays that measured their ability to inhibit microbial growth on agar plates, inhibit microbial growth in bacterial suspensions, and to inhibit the viability of adherent bacteria. Results Nanoparticles of between 50 and 75 nm were produced in PVA polymers. The production of nanoparticles was also confirmed by characteristic spectral peaks in ATR and XPS. The addition of silver or copper nanoparticles doubled the strength of PVA polymers but halved their elongation before fracture. Silver-containing PVA was cytotoxic but PVA containing copper alone was not cytotoxic. In the agar diffusion assay and inhibition of microbial growth in suspension only silver-containing lenses produced antibacterial activity, but silver and copper nanoparticle-containing lenses reduced bacterial adhesion to lenses. Conclusion both silver and copper nanoparticle-containing lenses were antibacterial, but this depended on the assay used. PVA containing only copper was not cytotoxic. This indicates the copper nanoparticle-containing lenses might be useful to control bacterial colonisation of lenses, and hence the production of bacterially-drive adverse events during lens wear.