Xiacong Zhang

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.

Sustainable lubrication of biomedicine hydrogels with high stability is important for their application in dry eye disease (DED) treatment, remaining challenge to achieve. We report a novel strategy to achieve sustainable superlubricity under ocular conditions based on the degradation of the thermosensitive P-C_nPEG hydrogel. Firstly, through adjusting the composition and chemical structure of P-C_nPEG complex, its aqueous solution undergoes an adaptive sol-to-gel transition at 25.1 °C during heating, forming a gel state upon injection onto the ocular surface (35 °C). Besides, the obtained P-C_nPEG hydrogel at 35 °C also shows superior performance, such as shear resistance, high transmittance (> 80%), rapid swelling, self-healing and Ca²⁺ responsiveness, making it well suitable for ocular applications. Then, in the tear environment of DED patients with high reactive oxygen species (ROS) content, P-C_nPEG hydrogel degrades within 6 days through the broken of the crosslinking sites. Degradation solution of each day presents ultra-low coefficients of friction (COF) under ocular conditions through the hydration effect. Finally, the excellent biocompatibility of the hydrogel demonstrates its potential for ocular applications. This study systematically discusses the mechanism of sustainable degradation-induced superlubricity of P-C_nPEG hydrogel, introducing a novel and promising strategy for DED treatment.

Dynamic covalent hydrogels exhibiting multi-responsive and antibacterial properties offer significant potential for biomedical applications, including smart wound dressings and controlled drug delivery. Herein, a series of amphiphilic quaternized copolymers (Q-C8PEG-n) with tunable quaternization degrees was synthesized from C8PEG via iodomethane addition and characterized by ¹H NMR, COSY, FTIR, UV-vis spectroscopy, DLS, TEM, and zeta potential analyses, confirming successful quaternization and micelle formation. These copolymers displayed thermosensitive behavior, with cloud point temperatures increasing due to enhanced hydrophilicity. Q-C8PEG-3 micelles, incorporating diethanolamine units, were crosslinked with phenylboronic acid-grafted hyaluronic acid (HA-PBA) to yield dynamic covalent hydrogels (Gel) through reversible boronic ester bonds stabilized by B-N coordination. The Gel exhibited multi-responsiveness, undergoing degradation in acidic or alkaline conditions and exposure to glucose or H₂O₂. SEM confirmed a porous microstructure, enabling efficient drug encapsulation, as demonstrated by the release of Nile red (NR). In vitro antibacterial tests revealed enhanced post-quaternization efficacy, with the Gel showing strong activity against S. aureus. This micelle-crosslinked platform synergistically combines tunable stimuli-responsiveness with inherent antibacterial properties, holding promise for applications in wound healing and tissue engineering.

Dry eye disease (DED) is a widespread ocular disorder that poses a growing threat to global eye health and creates a requirement for stable ocular lubrication. In this study, a strategy for achieving ocular superlubricity is proposed based on the reaction between a P-C₂PEGOH hydrogel and glucose in artificial tears. The dynamic boronic ester bonds in the P-C₂PEGOH hydrogel undergo a reversible competitive exchange reaction with glucose, leading to the dissociation of original cross-linking points and the release of hydrophilic polyethylene glycol (PEG)-based substrates. Both results of the reaction endow the hydrogel with glucose-responsive superlubricity. Friction tests show that the release of PEG-based substrates reduces the coefficient of friction (COF) of artificial tears from 0.0078 to 0.0037. PEG-based substrates form hydration layers that reduce shear stress of the interface through the hydration lubricating effect. Through varying the glucose concentration, the level of PEG-based substrates in the tears and the hydration capacity on the hydrogel surface can be modulated, thereby enabling glucose-responsive superlubricity. Furthermore, the presence of dynamic boronic esters containing boron-nitrogen coordination bonds endows the hydrogel with a self-healing capability, enabling it to recover its structural integrity after mechanical disruption. Moreover, cytotoxicity assays and in vivo biocompatibility evaluations confirm the biocompatibility of the hydrogel, highlighting its potential for ophthalmic applications.

Polyurethane (PU) foam, renowned for its structural versatility, elasticity, compressibility, and adaptability, has garnered significant attention for its use in flexible strain sensors due to its capability to detect mechanical deformation. This review presents a comprehensive analysis of both the studies and recent advancements in PU foam-based strain sensors, particularly those incorporating conductive materials. The review begins by examining the chemical composition and structural characteristics of PU foam, followed by a discussion of various fabrication methods and their effects on sensor performance. It also explores the sensing mechanisms, including piezoresistive, piezoelectric, and capacitive effects. Moreover, key applications in motion detection, health monitoring, and environmental and industrial sensing are examined. Finally, the review addresses technological advancements, current challenges, and prospects.

A series of novel amphiphilic alternating CPEG copolymers were synthesized through an amine–epoxy click reaction comprising aliphatic amine and polyethylene glycol diglycidyl ether (PEGDE). These polymers were characterized in detail via nuclear magnetic resonance (NMR), gel permeation chromatography (GPC), Fourier-transform infrared spectroscopy (FTIR), and thermogravimetric analysis (TGA) to confirm the successful synthesis. Due to their amphiphilic structure, these polymers display thermoresponsiveness, with tunable cloud points (Tcps) that are adjustable from 20.8 °C to 46.8 °C by altering the side-chain length of the aliphatic amine, varying the mixing ratios of copolymers, the solution’s pH, and salt additions. This tunable thermoresponsive behavior positions CPEG copolymers as promising candidates for a range of functional material applications.