Hang Zhang

This review summarizes recent advances in biopolymer-based IPN hydrogels. By leveraging topological entanglements, these systems overcome single-network limitations to drive innovative hard and soft tissue repair strategies.

Dynamic control over optical whiteness is promising for applications ranging from energy-efficient coatings to adaptive displays. However, current approaches rely on macroscopic structural transformations or externally imposed refractive-index contrasts, offering limited tunability and scalability. Here, we introduce a liquid crystal network (LCN) that undergoes reversible whitening through solvent-triggered disruption of supramolecular interactions. Exposure to polar protic solvents breaks hydrogen bonds and drives nanoscale phase segregation, generating domains that efficiently scatter visible light. This whitening mechanism enables rapid, robust, and fatigue-resistant switching, with scattering efficiencies exceeding 90% in 100 μm LCN films. By tailoring the molecular design, incorporating halogen-bonding dopants, and post-treatment with acid or base, the optical contrast and switching kinetics can be tuned. We demonstrate potential applications in biometric pattern recognition, underwater visibility enhancement, and solvent discrimination, establishing a materials platform towards dynamic scattering materials.

Inspired by organisms, we develop a hydrogen bond reconfiguration strategy to build supramolecular hydrogels via thermally reversible alignment. Quenching pre-stretched networks yields anisotropic hydrogels with outstanding mechanical performance.

Hydrogels, renowned for their remarkable water absorption capacity, have emerged as promising materials for oil-water separation. Nevertheless, the widespread application of traditional hydrogels remains challenging owing to their insufficient mechanical robustness, particularly in the hydrated and swollen state. In addition, hydrogels that simultaneously exhibit high strength, strong adhesion, excellent swelling capacity, and self-healing ability remain relatively rare. Herein, we present an "all-in-one" polyacrylonitrile (PAN) nanofibrous hydrogel through a "from-nanofibers-to-gel" strategy by controlling the alkaline hydrolysis time of PAN nanofibers. The resulting hydrogel exhibits exceptional mechanical strength and toughness (over 3.36 MPa at a strain of 1230%), adhesion (greater than 520 kPa), self-healing capability, and particularly outstanding swelling performance (more than 3600%). Notably, the hydrogels that have reached swelling equilibrium still remain good mechanical properties and can return to their original state with minimal shrinkage (<5% volume loss) after dehydration, enabling cyclic use. Furthermore, by integrating the thermoresponsive polymer PNIPAm and the photothermal material MXene into a PAN nanofibrous hydrogel, a photothermal-responsive PAN/MXene/PNIPAm hydrogel (PMP hydrogel) were obtained which demonstrates high efficiency in separating dye-contaminated oil/water mixtures. Additionally, as a solar-driven water evaporator, the PMP hydrogel effectively evaporates and degrades dye solutions, enabling the recovery of clean water. Benefiting from the hydrogel's exceptional mechanical strength and swelling capacity, the PMP hydrogel evaporator maintains 99.9% photodegradation efficiency for dyes and an 85.3% water recovery rate after 20 hydration-dehydration cycles.

Foldable mechanical metamaterials can toggle between multiple folding states with distinct properties. Each state differs in arrangement of elements and contact points, which change how mechanical signals and stresses distribute and propagate through the metastructure. Similarly, such folding states may influence how chemical signals travel, which may open new functional capabilities of these materials. Herein, we investigate how autocatalytic chemical waves propagate across passive metamaterial structures prepared from double network hydrogels with different geometry, hydrogel composition, and signalling chemistry. As folding states change, so do the signalling patterns; hinges and elements create new contact points that determine chemical signals’ pathways. Dynamically flipping between folding states allows for on-the-fly modulation of chemical signal propagation, including structure-aided transport, in both modelling and experiments. In such cases chemical signals hop across large distances aided by cycles of flipping through the folding states. Structuring chemical signal transport through foldable geometries, instead of propagation through the bulk, opens up unprecedented possibilities for user-defined control over spatiotemporal signal distribution in life-like materials.

Electrostatic flocking, traditionally used in decoration, has recently found emerging applications in diverse fields such as sensors, tissue engineering, evaporators and thermal management. By attaching high aspect ratio fibers onto a substrate through electrostatic flocking, it enables large‐scale control of fiber orientation, resulting in fibrous, porous, or furry structures with several benefits, including enhanced microforce detection sensitivity, large specific surface area, improved reflection/absorption, increased surface roughness, anisotropic surfaces, and strengthened mechanical properties. While challenges remain in achieving highly customized pattern for functional materials, electrostatic flocking holds promise in replicating natural fluffy structures, such as villi and cilia, which could lead to superior performance in biomimetic and functional applications. Despite recent significant progress, a comprehensive review on this technology for cutting‐edge applications is still lacking. This review aims to provide an in‐depth analysis of electrostatic flocking's broader applications and investigates the potential future of electrostatic flocking at the forefront of functional materials by examining the relationship between structure and performance in advanced materials. It begins with an overview of the technology's principles, followed by an exploration of its applications and morphological advantages, and concludes with a discussion of challenges, material selection, structural design, and future directions for this innovative technology.

Polyzwitterionic UCST hydrogels confined within hectorite nanostructures exhibit enhanced strength and tunable phase transitions dependent on thermal history, broadening their applications in smart soft materials.

Many biological tissues are mechanically strong and stiff but can still heal from damage. By contrast, synthetic hydrogels have not shown comparable combinations of properties, as current stiffening approaches inevitably suppress the required chain/bond dynamics for self-healing. Here we show a stiff and self-healing hydrogel with a modulus of 50 MPa and tensile strength up to 4.2 MPa by polymer entanglements in co-planar nanoconfinement. This is realized by polymerizing a highly concentrated monomer solution within a scaffold of fully delaminated synthetic hectorite nanosheets, shear oriented into a macroscopic monodomain. The resultant physical gels show self-healing efficiency up to 100% despite the high modulus, and high adhesion shear strength on a broad range of substrates. This nanoconfinement approach allows the incorporation of novel functionalities by embedding colloidal materials such as MXenes and can be generalized to other polymers and solvents to fabricate stiff and self-healing gels for soft robotics, additive manufacturing and biomedical applications.

The current synthesis methods, modifications, and characterizations of black titanium oxide (B-TiO _x ) as well as a nuanced understanding of its physicochemical properties and applications in green energy and environment are reviewed.

Biological tissues, such as tendons or cartilage, possess high strength and toughness with very low plastic deformations. In contrast, current strategies to prepare tough hydrogels commonly utilize energy dissipation mechanisms based on physical bonds that lead to irreversible large plastic deformations, thus limiting their load‐bearing applications. This article reports a strategy to toughen hydrogels using fibrillar connected double networks (fc‐DN), which consist of two distinct but chemically interconnected polymer networks, that is, a polyacrylamide network and an acrylated agarose fibril network. The fc‐DN design allows efficient stress transfer between the two networks and high fibril alignment during deformation, both contributing to high strength and toughness, while the chemical crosslinking ensures low plastic deformations after undergoing high strains. The mechanical properties of the fc‐DN network can be readily tuned to reach an ultimate tensile strength of 8 MPa and a toughness of above 55 MJ m⁻³, which is 3 and 3.5 times more than that of fibrillar double network hydrogels without chemical connections, respectively. The application potential of the fc‐DN hydrogel is demonstrated as load‐bearing damping material for a jointed robotic lander. The fc‐DN design provides a new toughening mechanism for hydrogels that can be used for soft robotics or bioelectronic applications.