Photoresponsive Superlubricity Achieved by a Host-Guest Hydrogel Releasing PEG for Ocular Applications

Prolonged exposure to visible light can disrupt tear-film stability and compromise ocular lubrication, potentially leading to eye fatigue, dryness, and the development of dry-eye disease, thereby highlighting the need for durable and long-lasting ocular lubrication. In this study, we develop a photoresponsive double-network hydrogel (PDNH) for the ocular environment that addresses these issues and achieves superlubricity. The PDNH is composed of a polyvinylpyrrolidone (PVP) hydrogel framework and a responsive supramolecular system of β-cyclodextrins/polyethylene glycol (β-CD/PEG) and competitive guest azobenzene derivative (Azo-C₂). Under visible-light irradiation, the competitive host-guest interaction between the β-CD/PEG supramolecule and Azo-C₂ lead to the release of the PEG chain ends from the β-CD cavities, allowing the PEG chains to diffuse toward the hydrogel surface. The strong hydrophilicity of PEG promotes water retention at the ocular surface, forming a stable lubricating layer that effectively reduces ocular friction. With continuous visible-light irradiation, the friction coefficient (COF) of the hydrogel gradually decreases and reaches its optimal state after 6 h of exposure, with the COF reduced by 25%, and its mechanical properties can remain at a high level. Its self-regulating lubrication capability minimizes dependence on frequent external lubricant administration. Moreover, its excellent biocompatibility highlights the promise as a smart ophthalmic lubricant, with the photoresponsive mechanism offering broad potential for biomedical systems and a novel route to ocular superlubricity in drug delivery.