Combined experiments and molecular simulations for understanding the thermo-responsive behavior and gelation of methylated glucans with different glycosidic linkages.

HYPOTHESIS: Elucidation of the micro-mechanisms of sol-gel transition of gelling glucans with different glycosidic linkages is crucial for understanding their structure-property relationship and for various applications. Glucans with distinct molecular chain structures exhibit unique gelation behaviors. The disparate gelation phenomena observed in two methylated glucans, methylated (1,3)-ß-d-glucan of curdlan (MECD) and methylated (1,4)-ß-d-glucan of cellulose (MC), notwithstanding their equivalent degrees of substitution, are intricately linked to their unique molecular architectures and interactions between glucan and water. EXPERIMENTS: Density functional theory and molecular dynamics simulations focused on the electronic property distinctions between MECD and MC, alongside conformational variations during thermal gelation. Inline attenuated total reflection Fourier transform infrared spectroscopy tracked secondary structure alterations in MECD and MC. To corroborate the simulation results, additional analyses including circular dichroism, rheology, and micro-differential scanning calorimetry were performed. FINDINGS: Despite having similar thermally induced gel networks, MECD and MC display distinct physical gelation patterns and molecular-level conformational changes during gelation. The network of MC gel was formed via a "coil-to-ring" transition, followed by ring stacking. In contrast, the MECD gel comprised compact irregular helices accompanied by notable volume shrinkage. These variations in gelation behavior are ascribed to heightened hydrophobic interactions and diminished hydrogen bonding in both systems upon heating, resulting in gelation. These findings provide valuable insights into the microstructural changes during gelation and the thermo-gelation mechanisms of structurally similar polysaccharides.

Injectable, Tough, and Thermoplastic Supramolecular Hydrogel Coatings with Controllable Adhesion for Touch Sensing.

Soft tissues in nature are anchored on the load-bearing structures of creatures, such as tendons, ligaments, and cartilages. However, mimetic hydrogel coatings that combine the unique properties of hydrogels (e.g., in situ formability, stimulus-responsiveness, strength controllability, environmental friendliness, and small molecular encapsulation) with the superior properties of substrates such as high elastic modulus and high tensile strength still require further exploration to achieve an adequately comprehensive performance. Herein, we report an approach for fabricating hydrogel coatings using an injectable, tough, and thermoplastic κ-carrageenan (κ-car)/poly(N-acryloyl glycinamide (NAGA)-co-vinyl imidazole (VI)) supramolecular hydrogel (κ-car/PNV hydrogel) with temperature-controlled adhesion by adjusting the contact at the hydrogel-substrate interface. The κ-car/PNV hydrogel with a mass ratio of NAGA to VI of 9:1 shows a sol-gel transition temperature of 85 °C, a compressive strain of 99%, a tensile strain of 1045%, fast self-recovery, durability, and the adhesive ability to handle irregular substrates. Furthermore, this supramolecular hydrogel coating forms strips and panels with slide rheostat-based touch sensing, which is minimally affected by water evaporation. This work facilitates the fabrication and application of hydrogel coatings as touch sensing devices to combine functional supramolecular hydrogels, surface coatings, and ionotronics.