Cilia-inspired hydrogel surfaces for low-pressure lubrication via interfacial water structuring

Abstract Lubrication plays a vital role in flexible electronics and medical devices, yet achieving stable low friction under low-pressure hydrodynamic conditions remains challenging. Existing approaches often lead to a coefficient of friction (COF) that increases with sliding velocity, due to the instability of interfacial water layers. Inspired by ocular surface structures, we developed a bio-inspired lubricating hydrogel (BLH) with nanowire arrays that confine interfacial water. This confined water remains stable under pressure, allowing COF to stay low and nearly independent of velocity. Under eyelid pressure (1.3-7.0 kPa), BLH achieved an ultra-low COF (0.0079-0.028), representing a 34-80% reduction compared to flat hydrogels (FH) and approaching that of natural corneal surfaces (0.014-0.037). The low friction was sustained over prolonged durations (≈ 6,000 s) and maintained at blinking-relevant speeds (≈ 4 cm/s). Tests using pig-eyeball rubbing and endoscope-probe models further demonstrated the robustness of this strategy, highlighting its promise for low-hysteresis coatings, flexible electronics, and medical devices.