Feeling comfortable is an important issue for contact lens wearers as contact lenses are worn for an extensive period of time. It has been shown that the in vitro friction coefficient of contact lenses is correlated to the degree of in vivo comfort, thus many studies focus on establishing friction testing methods for investigating the friction coefficient of contact lenses or contact lens care solution. We have previously demonstrated the lubricating property of poly-gamma-glutamic acid (gamma-PGA)-containing care solution, and it could reduce the high friction coefficient caused by lysozyme. However, the mechanism of how gamma-PGA-containing care solution reduces the lysozyme-induced friction coefficient of contact lenses is unclear. We investigated the bio-tribological effect of gamma-PGA on ionic contact lenses in the presence of lysozyme by testing load and velocity variations. The ability to remove lysozyme deposition by gamma-PGA and viscosity analysis of gamma-PGA-containing care solutions were also investigated to understand the potential mechanism. Our results showed that the friction coefficient of gamma-PGA-containing care solution with lysozyme was the lowest in both load and velocity variations, and gamma-PGA functions distinctly in the lysozyme-ionic contact lens system. We proposed a model of how gamma-PGA could reduce the friction coefficient in these two conditions.
