The effect of immobilisation strategies on the ability of peptoids to reduce the adhesion of P. aeruginosa strains to contact lenses

Aim

Previous studies have demonstrated that contact lenses coated with the antimicrobial cationic peptide Mel4, a derivative of melimine, can reduce the occurrence of keratitis. However, the antimicrobial activity of Mel4 weakened over time due to its susceptibility to proteolytic degradation. Oligo-N-substituted glycine peptoids such as TM5 and TM18 possess antimicrobial properties and are resistant to proteolytic breakdown. This study focused on exploring methods for covalently attaching these peptoids to contact lenses to enhance their durability and performance in vitro.

Methods

The peptoids TM5 and TM18 were covalently attached to etafilcon lenses via carbodiimide chemistry (EDC/NHS), oxazoline plasma, and plasma ion immersion implantation (PIII). The lenses were analysed using X-ray photoelectron spectroscopy (XPS), surface charge, and hydrophobicity. Inhibition of adhesion of multidrug-resistant Pseudomonas aeruginosa and cytotoxicity on corneal epithelial cells were evaluated. The impact of moist heat sterilization on activity was also assessed.

Results

XPS confirmed peptoid binding to lenses. Peptoid coatings slightly increased contact angles (≤23°) without affecting overall charge. Peptoids, bound via carbodiimide, inhibited P. aeruginosa adhesion by over 5 log10 CFU per lens, outperforming melimine, which required six times the concentration for a 3 log10 reduction. Peptoids attached via oxazoline or PIII reduced adhesion by > 5 log10 CFU. All covalent methods significantly reduced bacterial adhesion compared to untreated lenses (P < 0.0001). Peptoid-bound lenses were non-toxic to corneal epithelial cells. Sterilization did not affect carbodiimide-treated lenses but reduced the activity of oxazoline and PIII surfaces by 1–2 log10 CFU.

Conclusion

Peptoids TM5 and TM18 effectively reduced P. aeruginosa adhesion on lenses, with carbodiimide-bound surfaces retaining activity post-sterilization, showing promise for the development of antimicrobial contact lenses.