Macroscale Superlubricity of Gellan Gum-Based Hydrogel Enhanced with Hydrated Ions

Ocular lubrication is a critical component of the biological lubrication system. Factors such as tear film instability and corneal epithelial damage can lead to increased friction on the ocular surface during blinking, which negatively impacts quality of life and results in economic burden. Eye drops are commonly used therapeutic purposes. Due to the frequent movement (blinking, tear secretion, nasolacrimal drainage), their bioavailability is low, requiring frequent applications. In this study, methacylated gellan gum (GGMA) hydrogels were synthesized using methacrylic anhydride and low-acyl gellan gum as raw materials. The elastic modulus of GGMA hydrogel increased nearly threefold after introduction of alkali metal ions. Macroscopic superlubricity was achieved in friction experiments simulating the ocular environment. At a contact pressure close to 10 kPa, the COF was reduced to 0.004. Detailed friction experiments and sophisticated simulations revealed the underlying mechanism, showing that the superlubricity of GGMA hydrogel is attributed to the hydration properties of alkali metal ions adsorbed onto the hydrogel surface. The GGMA hydrogel exhibits excellent lubricating properties, offering promising potential for enhancing ocular lubrication and supporting eye health.