Antifatigue Hydration-Induced Polysaccharide Hydrogel Actuators Inspired by Crab Joint Wrinkles

Oligoadenine Strand Functionalized Polyacrylamide Hydrogel Film Exhibiting pH-Triggered High-Degree Inverse Shape Deformations

Smart shape-memory DNA hydrogels, which can respond to various types of external stimuli and undergo macroscopic shape deformations, have shown great potential in various applications. By constructing free-standing films, the deformation and response properties of these hydrogels can be further enhanced, and visualized deformation can be achieved. However, DNA hydrogels that can exhibit rapid and high-degree shape deformations, such as the inverse shape deformations, are still lacking. Herein, free-standing oligoadenine strand-functionalized polyacrylamide hydrogel films were developed that can exhibit reversible and high degree of inverse shape deformation upon cyclic pH changes. The oligoadenine strands exhibit a pH-stimulated reversible conformational transition between a flexible single-stranded state and parallel duplex A-motif structures, resulting in their role change in the film from negatively charged side chains to "head-to-head" crosslinking structures, driving a high degree of inverse shape deformation with a relative bending angle change of 223.7 % of the film, which is more than 5 times that of a film driven by pH-responsive i-motif structures, facilitating the development of bilayer hydrogel film actuators with potential in flexible sensors and robots.

Environmental and Wastewater Treatment Applications of Stimulus-Responsive Hydrogels

Stimulus-responsive hydrogels have emerged as versatile materials for environmental and wastewater treatment applications due to their ability to adapt to changing environmental conditions. This review highlights recent advances in the design, synthesis, and functionalization of such hydrogels, focusing on their environmental applications. Various synthesis techniques, including radical polymerization, grafting, and copolymerization, enable the development of hydrogels with tailored properties such as enhanced adsorption capacity, selectivity, and reusability. The incorporation of nanoparticles and bio-based polymers further improves their structural integrity and pollutant removal efficiency. Key mechanisms such as adsorption, ion exchange, and photodegradation are discussed, emphasizing their roles in removing heavy metals, dyes, and organic pollutants from wastewater. Additionally, this review presents the potential of hydrogels for oil-water separation, pathogen control, and future sustainability through integration into circular economy frameworks. The adaptability, cost-effectiveness, and eco-friendliness of these hydrogels make them promising candidates for large-scale environmental remediation.

Advancement in Soft Hydrogel Grippers: Comprehensive Insights into Materials, Fabrication Strategies, Grasping Mechanism, and Applications

Soft hydrogel grippers have attracted considerable attention due to their flexible/elastic bodies, stimuli-responsive grasping and releasing capacity, and novel applications in specific task fields. To create soft hydrogel grippers with robust grasping of various types of objects, high load capability, fast grab response, and long-time service life, researchers delve deeper into hydrogel materials, fabrication strategies, and underlying actuation mechanisms. This article provides a systematic overview of hydrogel materials used in soft grippers, focusing on materials composition, chemical functional groups, and characteristics and the strategies for integrating these responsive hydrogel materials into soft grippers, including one-step polymerization, additive manufacturing, and structural modification are reviewed in detail. Moreover, ongoing research about actuating mechanisms (e.g., thermal/electrical/magnetic/chemical) and grasping applications of soft hydrogel grippers is summarized. Some remaining challenges and future perspectives in soft hydrogel grippers are also provided. This work highlights the recent advances of soft hydrogel grippers, which provides useful insights into the development of the new generation of functional soft hydrogel grippers.

A review of chitosan-based shape memory materials: Stimuli-responsiveness, multifunctionalities and applications

Shape memory polymers (SMPs), as a type of smart materials, possess the unique shape memory and deformation recovery abilities. Hence, SMPs have been attracted extensive attentions and widely used in fields of electric devices, aerospace structures and biomedical engineering. Chitosan (CS), as a renewable natural biomass material, exhibits the excellent biocompatibility, biodegradability and antibacterial activities. Using biomass CS as SMPs matrix materials could greatly enhance the environmental friendliness and adaptability, promoting the applications in fields of biomedical engineering and smart devices. This paper provides a detailed overview of current research progress about CS-based SMPs, including diverse stimuli responsiveness, multifunctionalities and various applications. Though, the research on CS-based SMPs is still in the early stage, which exhibits extensive prospect and potential, and could be of significance in advancing smart biomedical technologies.

Electrically induced anisotropic assembly of chitosan with different molecular weights

Anisotropic hydrogel is emerging as an important soft matter in the field of bionics and bioactuators, owing to its outstanding mechanical toughness and strength. Understanding the dynamic construction process of anisotropic hydrogel is beneficial for matching subsequent application. In this work, we establish an electrical field in microfluidics for the in-situ real time visualization of anisotropic assembly of chitosan, an amino polysaccharide. Polarized light microscopy is adopted to observe the dynamic growth of chitosan with different molecular weights. The results demonstrate that electrical signal has a profound influence on anisotropic assembly process of chitosan. It is interesting to notice that high oriented structure can be found in chitosan hydrogel with large molecular weight, which exhibits a dense and compact structure. This work provides a new perspective for predicting and controlling the formation of different molecular weights anisotropic chitosan hydrogels, which permit the rational design of chitosan hydrogels with excellent mechanical properties and specific functions.

Highly Adhesive, Stretchable, and Antifreezing Hydrogel with Excellent Mechanical Properties for Sensitive Motion Sensors and Temperature-/Humidity-Driven Actuators

Conductive hydrogels as flexible wearable devices have attracted considerable attention due to their mechanical flexibility and intelligent sensing. How to endow more and better performance, such as high self-adhesion, stretchability, and wide application temperature range for traditional hydrogels and flexible sensors is a challenge. Herein, a stretchable, self-adhesive, and antifreezing conductive hydrogel with multiple networks and excellent mechanical properties was prepared by a two-step method for its application in sensitive motion sensors and temperature-/humidity-driven actuators. First, quaternary chitosan (QCS) was introduced into the network of an acrylamide (AM) and 1-vinyl imidazole (VI) copolymer initiated by UV-photoinitiated radical polymerization. Then, the double-network hydrogel was immersed in a FeCl₃ solution to fabricate the P(AAm-co-VI)/QCS-Fe³⁺ ionic hydrogel with multiple physical networks. The properties of the hydrogel were controllable and adjustable. The toughness of the ionic hydrogel could reach up to 654.4 kJ/m³, the fracture strength could reach 253.1 kPa, and the compressive strength reached 8.4 MPa at an 80% compression strain. The multiple physical networks improved the mechanical properties and the quick resilience of the hydrogel. A large amount of FeCl₃ in the network greatly enhanced the ionic conductivity. Meanwhile, hydrogen bonds with water molecules inhibit the formation of ice crystals between zero water molecules and enhance the freezing resistance of P(Aam-co-VI)/QCS hydrogels. The active group on the QCS chain provided adhesiveness to various substrates for hydrogels. The P(AAm-co-VI)/QCS-Fe³⁺ hydrogel-based sensor showed high sensitivity, which can detect human movement and pulse, with a gauge factor of 2.37. Finally, due to the different dehydration rates of the P(AAm-co-VI)/QCS-Fe³⁺ and P(AAm-co-VI)/QCS hydrogel, a double-layer temperature/humidity-driven actuator was fabricated, expanding the application of conductive hydrogels.