Hydrogels have been the subject of significant research in the field of friction due to their exceptional lubricating properties. In this study, the G-quadruplex hydrogel with high selectivity for K⁺ ions was formed by introducing a mixture of G, 2-formylphenylboronic acid, and polyethylene glycol diamine into simulated artificial tears solution with high transparency, and an ultra-low coefficient of friction (COF) of about 0.004 was obtained based on the simulated ocular environment, thus achieving macroscopic superlubricity. In friction pairs simulating the ocular environment, to assess the frictional performance of the G-quadruplex hydrogel as both a lubricant and a friction pair based on the simulated ocular environment, we conducted experiments considering various factors such as concentration, sliding speed, and stress. Through these experiments, it was found that superlubricity was achieved when the G-quadruplex hydrogel was applied as lubricant or friction pair. This effect was attributed to the three-dimensional network structure and hydrophilicity of the hydrogel, which facilitated the formation of a highly bearing and flowing hydration layer, promoting macroscopic superlubricity. Compared to the G-quadruplex hydrogel with low concentration, the high concentration hydrogel (75 mM) exhibited increased mechanical strength and robustness in superlubricity. Combined with biocompatibility experiments, our synthesized G-quadruplex hydrogel has excellent biocompatibility and offers a novel approach to achieve superlubricity in ocular drug delivery.

Polymers have complex molecular structures that often lead to inter-chain friction and hinder movement, making it difficult to achieve superlubricity. However, in the field of hydration lubrication, the electronegative interface of ceramics readily adsorbs water molecules, creating a protective water film that covers the frictional interface and effectively reduces friction. To achieve hydration lubrication, it is essential to create a continuous lubricating film by selectively enriching specific functional groups of adsorbed water molecules from the polymer solution onto the ceramic surface. By adsorbing a hydrated layer composed of polyvinylpyrrolidone with pyrrolidone groups onto a negatively charged Si₃N₄/sapphire interface, we have enabled the formation of a continuous lubricating film. Research has found that the interaction between the polymer chain structure of Polyvinylpyrrolidone molecules (such as PVP10000) in solution and water molecules could exhibit excellent superlubricity. Under contact pressure exceeding 198 MPa, the coefficients of friction could be reduced to 0.004-0.007. Through detailed surface analyses and sophisticated simulations, we uncovered the underlying mechanism. The pyrrolidone moieties of PVP formed hydrogen bonds with the Si₃N₄ surface, transforming the initially difficult frictional interface into a PVP/sapphire interface with significantly reduced sliding energy barriers. These findings highlight the vital role of PVP in superlubricity and hydration lubrication, and provide a theoretical and experimental basis for the design of materials and lubricants with exceptional lubricating properties.

Electron energy dissipation is an important energy dissipation pathway that cannot be ignored in friction process. Two-dimensional zeolite imidazole frameworks (2D ZIFs) and fluorine doping strategies give 2D Zn-ZIF and 2D Co-ZIF unique electrical properties, making them ideal materials for studying electron energy dissipation mechanism. In this paper, based on the superlubricity modulation of 2D fluoridated ZIFs, the optimal tribological properties are obtained on the 2D F-Co-ZIF surface, with the friction coefficient as low as 0.0010. Electrical experiments, density functional theory (DFT) simulation, and fluorescence detection are used to explain the mechanism of fluorine doping regulation of tribological properties from the two stages, namely energy transfer and energy release. Specifically, the energy will transfer into the friction system through the generation of electron–hole pairs under an external excitation, and release by radiation and non-radiation energy dissipation channels. Fluorination reduces energy transfer by altering the electronic properties and band structures of ZIFs, and slows down the charge transfer by enhancing the shielding efficiency, thus slowing the non-radiative energy dissipation rate during the energy release stage. Our insights not only help us better understand the role of fluorine doping in improving tribological properties, but also provide a new way to further explore the electron energy dissipation pathway during friction.