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Programmable asymmetric hydrogels with tunable structure/shape or physical/chemical properties in response to external stimuli show particular significance in smart systems, but there is lack of simple, rapid, and cheap strategy to design such hydrogel systems. Herein, we report a one-step electrodeposition method to construct chitosan asymmetric hydrogels with tunable thickness and pore size that can be conveniently modulated by the process parameters. Our approach greatly simplifies the process of hydrogel preparation with complex shapes and asymmetric structure organization. The formation mechanism of asymmetric structure has been proposed, based on gelation behavior and entanglement of chitosan chains in the hydrogel-solution system under the electric field. By changing the shape of the electrodes, hydrogels with the morphology of strip, tube, flower, etc. can be obtained precisely and conveniently. They can perform programmable 2D to 3D smart dynamic deformation under pH and metal ions stimulation, indicating the broad application potential in soft robot and biosensor areas., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

The construction of polymeric nanocomponents into a hierarchical structure poses great importance for subsequent biomedical applications. Herein, we report for the first time the electroassembly of chitin nanoparticles (14 nm ± 3 nm from transmission electron microscopy) to construct thick and freestanding hydrogels, which can be further dried to obtain high porous and tough aerogels for wound healing. The electroassembly is a simple, straightforward, and controllable process, which crucially depends on the pH of the chitin nanoparticle suspension and the degree of deacetylation of chitin. Interestingly, the electroassembly of chitin nanoparticles is completely reversible, suggesting the physical assembly feature of the freestanding hydrogel. By using supercritical CO 2 drying and freeze-drying, chitin aerogels and cryogels can be facilely obtained. Because of the intriguing features (i.e., large surface area, interconnected porous structure, and enhanced hydrophilicity), chitin aerogels demonstrate adorable performance to accelerate the healing of wounds.

[Display omitted] • Oriented β-chitin nanofiber hydrogel was obtained by electroassembly. • The hydrogel structure and properties can be easily modulated by the process parameters. • Oriented cryogel shows superior properties in cell proliferation and wound healing. • The strategy provides a preferential route to obtain anisotropic natural nanogels. The construction of natural polymeric nanocomponents with tunable hierarchical structure in a simple and controllable process remains a great challenge. Herein, an oriented β-chitin nanofiber hydrogel was fabricated by an electro-assembly process in water phase, during which the internal structure of the hydrogel was facilely tuned by the process parameters. The orientation of the β-chitin nanofibers hydrogel was influenced by the concentration of nanofibers and pH, and strengthened by increased current density and longer deposition time. Cryogels with extraordinary physical and biological properties were subsequently obtained by freeze drying. When used as wound dressing in cell and animal models, the oriented β-chitin nanofiber cryogels could significantly promote cell proliferation and accelerate wound healing, outperforming the healing effect of unoriented structure. [ABSTRACT FROM AUTHOR]

• CNF/metal hydrogels are created by electrochemically induced counterion exchange. • The electrochemical counterion exchange is straightforward, mild and quick. • The hydrogel displays enhanced thermal degradation, improved mechanical strength. • The hierarchical nanoporous hydrogel exhibits anti-microbial performance. The fabrication of polymeric composite hydrogel with hierarchical structure in a simple, controllable, and straightforward process poses great importance for manufacturing nanomaterials and subsequent applications. Herein, we report a one-step and template-free counterion exchange method to construct free-standing carboxylated cellulose nanofiber composite hydrogels. Metal ions were electrochemically and locally released from the electrode and chelated with carboxylated cellulose nanofibers, leading to the in-situ formation of composite hydrogels. The properties of composite hydrogels can be easily programmed by the type of electrode, current density, and electrodeposited suspension. Significantly, the composited hydrogels exhibited interconnected nanoporous structure, enhanced thermal degradation, improved mechanical strength and antibacterial activity. The results suggest great potential of anodic electrodeposition to fabricate nanofiber/metal composite hydrogels. [ABSTRACT FROM AUTHOR]

Pea protein has attracted attentions as an alternative for soy protein, but its weaker gelling properties has limited its applications in food formulations. This research reports a heat-induced strong and elastic gel from pea protein isolate (PPI) pre-treated by a modified pH-shifting method. The scanning electron microscopy (SEM) observation and rheological measurement revealed that the formation of three-dimensional (3D) coagulum for pea protein at pH 12 by extending the alkali holding time (1, 24 and 48 h) and such coagulum maintained their structure when adjusting pH back to neutral. Further heating the pH-shifted PPI suspension at 92 °C led to gels of densely cross-linked polymer-like network with thin connective walls and pore size of 1–2 μm. Such uniform polymer-like gel network microstructure obtained in this work might be related to a high level of pea protein unfolding during pH-shifting treatment, which made the protein chain flexible and created more active sites to promote molecular interactions including hydrogen bonds and hydrophobic interactions when the protein was neutralized and heated. Notably the gel mechanical strength was dramatically increased to 21 kPa, accompanied by excellent elasticity and water holding capacity (>95%). The modified method of pH-shifting process has provided a new approach for preparation of pea protein gels with superior strength, thus may enable wider applications of pea protein applications in food formulations where gelling and texturization functions are required. [Display omitted] • pH shifting method enhanced the gelling capacity of pea protein at neutral pH. • Long-time holding at extreme alkali pH resulted in elastic pea protein hydrogels. • Hydrogen bonds plays more important role in elastic pea protein hydrogels. • Evenly distributed protein network was formed in elastic pea protein hydrogels. • Gel microstructure shows relation to the corresponding mechanical properties. [ABSTRACT FROM AUTHOR]