Gold nanoparticles-loaded contact lenses for laser protection and Meibomian Gland Dysfunction (MGD) dry eye treatment

Abstract

Laser based devices are ubiquitous in many fields which has resulted in an increase in ocular injuries from laser exposure. Glasses for laser protection are available but contact lenses that block certain wavelengths could be a less bulky alternative. Here, we focus on developing a contact lens for protecting eyes from accidental exposure to a green laser by incorporation of gold nanoparticles that exhibit a local maximum in absorbance as a tunable wavelength due to the localized surface plasmon resonance (LSPR) effect. The particles are incorporated in a poly vinyl alcohol (PVA) contact lens because PVA offers the twin benefits of stabilizing gold nanoparticles during manufacturing by Turkevich method and excellent biocompatibility and high-water content. The monodispersed gold nanoparticles of the desired size (11.75 ± 1.09 nm) were prepared by Turkevich method with PVA as the stabilizer. The particles were separated out by anti-solvent precipitation and then redispersion to achieve the desired concentration, and finally crosslinked by freezing-thawing cycling to form a PVA lens loaded with gold nanoparticles (PVA GoldinLens). The gold nanoparticles remain well-dispersed in the lens for all gold nanoparticle loadings (0%, 0.25%, 0.5%, 1%, 2% and 4%, wt% in dried lenses). The transmittance spectra of the PVA GoldinLenses exhibit a minimum at 520 nm due to the LSPR effect of the 12 nm gold nanoparticles. The transmittance was reduced in the entire wavelength range, as is typical in laser protection glasses but the decrease is more pronounced around 520 nm. The laser protection efficacy enhances with particle concentration but becomes relatively independent of particle loading at higher concentration reaching a maximum value of 66.7%. To further improve the laser protection, we explore an alternative approach of manufacturing the gold particles inside two commercial contact lenses (Acuvue TruEye and Moist) by soaking the lenses in gold precursor solution (0.25–1%, wt%) followed by reduction by soaking in solution of 5% (wt%) sodium borohydride to form the particles. This process leads to formation of about 100 nm size particles in the lenses. Incorporation of particles in both commercial lenses offers superior absorption compared to the PVA lens at comparable loadings with > 90% blocking of laser at about 3% (wt% in dried lens) loading. However, the absorbance is not tuned to the green laser due to the larger particle sizes and particle aggregates which result in light transmittance decreasing significantly in the entire wavelength range. Based on comparing the absorption spectra and laser blocking of the lenses with commercial laser blocking glasses, the TruEye GoldinLens with 0.75% particles appears to be a good potential alternative. In all cases, absorption of laser leads to localized heating which could damage tissue but on the other hand could potentially also be useful in treating indications in which warming eyelids is beneficial such as dry eyes. Laser exposure increases temperature to higher than the melting point of the meibomian lipids which is critical for treating the gland dysfunction (MGD) dry eye disease by local heating. This work advances the field of incorporation of gold nanoparticles in contact lenses and other similar gels for a broad set of applications including laser-protection, and treatment of dry eyes and color blindness.