Tuning the Viscoelastic Behavior of Hybrid Hydrogels Composed of a Physical and a Chemical Network by the Addition of an Organic Solvent

The influence of isopropanol (IPA) addition on the viscoelastic behavior of hybrid hydrogels which were prepared from chemically cross-linked copolymers of <i>N</i>,<i>N</i>-dimethyl­acrylamide (DMA), 2-(<i>N</i>-ethyl­perfluoro­octane­sulfonamido)­ethyl methacrylate (FOSM) and cinnamoyl­oxyethyl acrylate was investigated by dynamic oscillatory shear. The hybrid gels were composed of a supramolecular network formed by phase-separated FOSM nanodomains that served as physical cross-links and a chemical network derived from photo-cross-linking the cinnamate groups. The linear viscoelastic (LVE) behavior of the gels was tunable by changing the solvent ratio (IPA/water) and/or temperature. When the swelling solvent was pure water or pure IPA, the materials were hydrogels and organogels, respectively. When the IPA concentration increased from a molar ratio of IPA:FOSM of zero to 80:1, the cross-link density of the gels decreased due to weakening of the physical network as a result of solvation of the hydrophobic interactions by IPA. Above an IPA:FOSM ratio of 80:1, essentially only the covalent network persisted and the gels behaved as elastic solids. The design of these hydrogels/organogels provides three degrees of freedom for tuning the LVE properties: copolymer composition, temperature, and solvent. They also provide responsive behavior of the gels to changes of temperature and/or solvent

Tough Stretchable Physically-Cross-linked Electrospun Hydrogel Fiber Mats

Nature uses supramolecular interactions and hierarchical structures to produce water-rich materials with combinations of properties that are challenging to obtain in synthetic systems. Here, we demonstrate hierarchical supramolecular hydrogels from electrospun, self-associated copolymers with unprecedented elongation and toughness for high porosity hydrogels. Hydrophobic association of perfluoronated comonomers provides the physical cross-links for these hydrogels based on copolymers of dimethyl acrylamide and 2-(N-ethylperfluorooctane sulfonamido)­ethyl methacrylate (FOSM). Intriguingly, the hydrogel fiber mats show an enhancement in toughness in comparison to compression molded bulk hydrogels. This difference is attributed to the size distribution of the hydrophobic aggregates where narrowing the distribution in the electrospun material enhances the toughness of the hydrogel. These hydrogel fiber mats exhibit extensibility more than double that of the bulk hydrogel and a comparable modulus despite the porosity of the fiber mat leading to >25 wt % increase in water content

Tough Stretchable Physically-Cross-linked Electrospun Hydrogel Fiber Mats

Nature uses supramolecular interactions and hierarchical structures to produce water-rich materials with combinations of properties that are challenging to obtain in synthetic systems. Here, we demonstrate hierarchical supramolecular hydrogels from electrospun, self-associated copolymers with unprecedented elongation and toughness for high porosity hydrogels. Hydrophobic association of perfluoronated comonomers provides the physical cross-links for these hydrogels based on copolymers of dimethyl acrylamide and 2-(N-ethylperfluorooctane sulfonamido)­ethyl methacrylate (FOSM). Intriguingly, the hydrogel fiber mats show an enhancement in toughness in comparison to compression molded bulk hydrogels. This difference is attributed to the size distribution of the hydrophobic aggregates where narrowing the distribution in the electrospun material enhances the toughness of the hydrogel. These hydrogel fiber mats exhibit extensibility more than double that of the bulk hydrogel and a comparable modulus despite the porosity of the fiber mat leading to >25 wt % increase in water content

Strain-Promoted Cross-Linking of PEG-Based Hydrogels via Copper-Free Cycloaddition

The synthesis of a 4-dibenzocyclooctynol (DIBO) functionalized poly­(ethylene glycol) (PEG) and fabrication of hydrogels via strain-promoted, metal-free, azide–alkyne cycloaddition is reported. The resulting hydrogel materials provide a versatile alternative to encapsulate cells that are sensitive to photochemical or chemical cross-linking mechanisms