Synthesis, characterization and biocompatibility of hybrid hydrogels based on alginate, κ-carrageenan, and chitosan filled with montmorillonite clay.

New hybrid hydrogel composites based on a mixture of natural polysaccharides (sodium alginate, κ-carrageenan, and chitosan) filled with the clay mineral of natural origin, montmorillonite (MMT), were studied. The structure of intercalated/flocculated MMT distribution in the interpenetrating network of polysaccharide matrix was characterized using FTIR, X-ray diffraction, and SEM techniques. Swelling kinetics was investigated using the weight analysis, whereas the phase transition of water in the composition of hybrid hydrogels, by DSC method. Their biosafety was estimated using the Nelyubov method, germination test on cress (L. sativum) seeds, and metabolic fingerprinting of microbial communities and dehydrogenase assay. The obtained results indicated promising water-retaining properties of the synthesized materials. The hydrogels had a good sorption affinity for cadmium (Cd) ions confining bioavailability of the selected toxic heavy metal. They were safe for soil microorganisms and did not generate metabolic stress for them. Moreover, they did not reduce the viability of pea seeds. Thus, the development of biosafe hybrid hydrogel composites with a comprehensive, good effect on the environment could be considered as successful.

Strain Engineering of Ion-Coordinated Nanochannels in Nanocellulose.

Expanding the interlayer spacing plays a significant role in improving the conductivity of a cellulose-based conductor. However, it remains a challenge to regulate the cellulose nanochannel expanded by ion coordination. Herein, starting from multiscale mechanics, we proposed a strain engineering method to regulate the interlayer spacing of the cellulose nanochannels. First-principles calculations were conducted to select the most suitable ions for coordination. Large-scale molecular dynamics simulations were performed to reveal the mechanism of interlayer spacing expansion by the ion cross-linking. Combining the shear-lag model, we established the relationship between interfacial cross-link density and interlayer spacing of an ion-coordinated cellulose nanochannel. Consequently, fast ion transport and current regulation were realized via the strain engineering of nanochannels, which provides a promising strategy for the current regulation of a cellulose-based conductor.

Fabrication of Cellulose-Graphite Foam via Ion Cross-linking and Ambient-Drying.

Conventional plastic foams are usually produced by fossil-fuel-derived polymers, which are difficult to degrade in nature. As an alternative, cellulose is a promising biodegradable polymer that can be used to fabricate greener foams, yet such a process typically relies on methods (e.g., freeze-drying and supercritical-drying) that are hardly scalable and time-consuming. Here, we develop a fast and scalable approach to prepare cellulose-graphite foams via rapidly cross-linking the cellulose fibrils in metal ions-containing solution followed by ambient drying. The prepared foams exhibit low density, high compressive strength, and excellent water stability. Moreover, the cross-linking of the cellulose fibrils can be triggered by various metal ions, indicating good universality. We further use density functional theory to reveal the cross-linking effect of different ions, which shows good agreement with our experimental observation. Our approach presents a sustainable route toward low-cost, environmentally friendly, and scalable foam production for a range of applications.

Programmable and Reversible 3D-/4D-Shape-Morphing Hydrogels with Precisely Defined Ion Coordination.

Precise and programmable control of reversible deformations of hydrogels has important implications for bionics. This work reports on programmable three-dimensional (3D) deformations and thermoresponsive actuation of polymer hydrogels in a well-defined manner. Precise infiltration of Fe3+ with periodic patterns is additionally used to cross-link the local polymer network through ionoprinting with a patterned electrode array. The patterned Fe3+ cross-linking generates periodic undulations in cross-link density, stiffness, and thermoresponsiveness. The internal stress induces 3D helical structures with tunable chirality and dimensions. The differential thermoresponsiveness imbues a fourth dimension to the shape deformations. Moreover, sequential ionoprinting generates well-defined in-plane periodic distributions of differential modulus and responsiveness, leading to 3D/4D umbrella-like origami upon temperature triggers.

Ion-Cross-Linking-Promoted High-Performance Si/PEDOT:PSS Electrodes: The Importance of Cations' Ionic Potential and Softness Parameters.

PEDOT: PSS has been studied as a silicon-based binder due to its inherent superior electricity and electrochemical stability. However, it cannot effectively alleviate the huge volume changes of silicon during lithiation/delithiation due to its linear structure, resulting in poor cycling stability. Ion-cross-linking is a usual method to cross-link linear polymers into 3D structures. In this paper, multivalent cations of the 5th period and Group 2 cross-linked PEDOT:PSS were applied as silicon anode binders and studied systematically. It was found that the variation trend of viscosity and conductivity of PEDOT:PSS after cross-linking was consistent with that of ionic potential and softness parameters of multivalent cations. The mesostructure of a binder after cross-linking is influenced by the solubility product constant of sulfites or hydroxides of cations and the growth characteristics of crystals. An Sn4+-cross-linked binder displayed increased viscosity and electrical conductivity and higher reduced modulus and hardness due to its positive softness parameter and higher ion potential. The Si electrode with the Sn4+-cross-linked binder showed improved cycling stability (1876.4 mAh g-1 compared with 1068.4 mAh g-1 of the electrode with the pure PEDOT:PSS binder after 100 cycles) and superior rate capability (∼800 mAh g-1 at an ultrahigh current density of 8.0 A g-1).

In Vitro and in Vivo Evaluation of the Wound Healing Properties of Nanofibrillated Cellulose Hydrogels.

Current trends in wound care research move toward the development of wound healing dressings designed to treat different types of wounds (e.g., burns and chronic wounds) and toward tailoring treatments for different stages of the wound healing process. In this context, the development of advanced nanotherapeutic materials is highlighted as a promising strategy to efficiently control specific phases of the wound healing process. Here, Ca2+-cross-linked wood-derived nanofibrillated cellulose (NFC) hydrogels are evaluated as wound healing dressings. In vitro biocompatibility assays were performed to study the interaction of the NFC hydrogels with cellular processes that are tightly related to wound healing. Moreover, an in vivo dermo-epidermic full thickness wound healing model in rat was used to uncover the wound healing ability of the Ca2+-cross-linked NFC hydrogels. The in vitro experiments showed that the NFC hydrogels were able to support fibroblast and keratinocyte proliferation. A potential effect of the hydrogels on triggering keratinocyte differentiation was furthermore proposed. In vivo, the NFC hydrogels stimulated healing without causing any adverse local tissue effects, potentially owing to their moisture-donating properties and the herein discussed aiding effect of the Ca2+-cross-linker on epidermal generation. Thus, this work extensively demonstrates the wound healing ability of NFC hydrogels and presents an important milestone in the research on NFC toward advanced wound healing applications.