Effect of Hydrophobic Side Group on Structural Heterogeneities and Mechanical Performance of Gelatin-Based Hydrogen-Bonded Hydrogel

Abstract

Hydrogen bonds stabilized by hydrophobic side groups have been widely applied to realize high toughness of hydrogels. Herein, we studied the effect of the content of the hydrophobic methyl side group on the structure and mechanical properties of tough hydrogen-bonded gelatin/poly (methacrylic acid–co-acrylic acid) (G/M x -A y ) hydrogels by alternating the content of methacrylic acid (MAA) in the methacrylic acid–acrylic acid copolymer (MAA-co-AA). The content of MAA did not affect the hydrogen-bond formation between the MAA-co-AA and gelatin but affected the phase-separated structure. With an increase in the MAA content, the local structure of the hydrogels with similar water content transformed from a “network” structure to a “bicontinuous” phase-separated structure and to a phase-separated structure with wide size distribution. The hydrogels with the same structure exhibited similar viscoelastic behaviors, and the G/M x -A y hydrogels with “bicontinuous” phase separation exhibited the best mechanical properties with an optimal Young’s modulus of ∼7.5 MPa and fracture tensile stress of ∼10 MPa.

Mineral Tanning‐Inspired Metal Ions Coordination Hydrogels with Outstanding Mechanical Strength and Toughness for Flexible Force Sensors

“…The slopes of Zr‐HG Soaking , Zr‐HG Tanning , Fe‐HG Soaking , and Fe‐HG Tanning were 3.18, 3.68, 2.86, and 4.09, respectively, indicating all these hydrogel samples bearing polymer networks with the rough surface. [ 28 ] Commonly, the larger slope means the higher crosslinking density of the network. Therefore, SAXS results further deciphered that the mineral tanning strategy could increase the crosslinking density, thus improving the mechanical properties of hydrogels.…”

Structuring and Shaping of Mechanically Robust and Functional Hydrogels toward Wearable and Implantable Applications

“…Microphase separations can be induced by noncovalent interactions among polymer networks, [ 129 ] including hydrophobic associations, [ 130–133 ] electrostatic interactions, [ 134–139 ] and hydrogen bonds. [ 140–144 ] The produced microdomains are composed of polymer chains in strong physical interactions, acting as dynamic and reversible physical crosslinks in polymer networks, and thus dramatically improving mechanical performance of hydrogels. For example, alkyl side chains can usually form hydrophobic domains to crosslink polymer networks.…”

“…The hydrogel with a bicontinuous phase separation exhibited the best mechanical performance. [ 143 ]…”

Phase-Separation-Induced Porous Hydrogels from Amphiphilic Triblock Copolymer with High Permeability and Mechanical Strength

“…One is that pores act as defects, causing stress concentration and facilitating crack initiation when subjected to a load . The second is that these hydrogels often lack an energy dissipation mechanism. ,− Accordingly, a direct strategy to enhance the mechanical strength of porous hydrogels is to introduce energy dissipation mechanisms. , Recent research has shown that employing an energy dissipation mechanism in porous hydrogel can enhance the mechanical strength . However, the enhancement in most porous hydrogels is still limited , with fracture energy on the order of tens of J/m 2 , work of extension of ∼1000 kJ/m 3 , and fracture strain barely exceeding 200%.…”