Rational Fabrication of Anti‐Freezing, Non‐Drying Tough Organohydrogels by One‐Pot Solvent Displacement

Abstract

Tough hydrogels, polymeric network structures with excellent mechanical properties (such as high stretchability and toughness), are emerging soft materials. Despite their remarkably mechanical features, tough hydrogels exhibit two flaws (freezing around the icing temperatures of water and drying under arid conditions). Inspired by cryoprotectants (CPAs) used in the inhibition of the icing of water in biological samples, a versatile and straightforward method is reported to fabricate extreme anti-freezing, non-drying CPA-based organohydrogels with long-term stability by partially displacing water molecules within the pre-fabricated hydrogels. CPA-based Ca-alginate/polyacrylamide (PAAm) tough hydrogels were successfully fabricated with glycerol, glycol, and sorbitol. The CPA-based organohydrogels remain unfrozen and mechanically flexible even up to -70 °C and are stable under ambient conditions or even vacuum.

Redox‐Active Iron‐Citrate Complex Regulated Robust Coating‐Free Hydrogel Microfiber Net with High Environmental Tolerance and Sensitivity

“…It is observed that the hydrogel microfiber maintains good elasticity at −40 °C with almost coincident tensile curve to that at 25 °C, and the fiber becomes brittle lower than −50 °C. The frost resistance of hydrogel microfiber is attributed to the presence of glycerol, which is known to significantly inhibit ice crystallization in hydrogel systems 32,33…”

Softening and Shape Morphing of Stiff Tough Hydrogels by Localized Unlocking of the Trivalent Ionically Cross‐Linked Centers

“…In addition, this method is expected to be compatible with various patterning or printing techniques . Despite the current proof‐of‐concept demonstration of the softening the Fe 3+ ‐Ca/alginate/PAAm tough hydrogels, we believe this method can be applied to vary the stiffness of other tough hydrogels, tough organohydrogels, or elastomers strengthened by Fe 3+ . Therefore, the present study should not only provide a platform to the precisely engineering the mechanical properties, but also give us a better understanding and improve mimicking the biological stiff‐to‐soft transition of biological tissues.…”

Biomimetic Extreme‐Temperature‐ and Environment‐Adaptable Hydrogels

“…By substituting the incorporated water of the hydrogels with an organic solvent, totally or in parts, organohydrogels are formed with depressed freezing point, altered mechanical properties [60] and also endowed with enhanced liquid retention in arid environments. [86] The term organohydrogel was probably first mentioned by Gua and Dong in 1997 in their work about organic phase enzyme electrodes, a work related to biosensing, [87] though, the authors did not utilize the antifreezing property of their organohydrogel, which comprised of polyhydroxyl cellulose (PHC), a mixture of poly(vinyl alcohol) (PVA) and carboxymethyl hydroxyethyl cellulose (CMHEC), and a mixture of dimethylformamide (DMF) and water as solvent. They were, however, able to immobilize enzymes in the organohydrogel, which maintained their enzymatic activity, and sense organic peroxides, phenolic compounds and bilirubin.…”

“…Since then, organohydrogels have attracted attention in the 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 scientific community due to its advanced properties, such as high mechanical toughness, [60,86] long-term stability and resistance versus hot and cold environments. [87] Organohydrogels consist of hydrophilic and hydrophobic domains within the same microenvironment, rendering them able to incorporate simultaneously hydrophilic and hydrophobic cargo molecules, [88] such as solvents, dyes and antimicrobials.…”