Mechanically tough and recoverable hydrogels via dual physical crosslinkings

Abstract

Development of functional tough hydrogels with new network structures and energy dissipation mechanisms has great promise for many applications. Here, a new type of physical hydrogel crosslinked by hydrophobic association and hydrogen bonds was synthesized by a facile micellar copolymerization of hydrophobic methyl acrylate (MA) monomers and hydrophilic N-hydroxyethyl acrylamide (HEAA) monomers in the presence of Tween80 micelles. Strong hydrophobic association between inner MA and Tween80 and hydrogen bonds between external polyHEAA and Tween80 provide two distinct crosslinkers to construct mechanically tough and recoverable network. Mechanical properties of polyHEAA-MA@Tween80 hydrogels strongly depended on network components (HEAA, MA; Tween80 concentrations). At optimal conditions, the hydrogels can achieve fracture stress of 700 kPa, fracture strain of 1687 mm/mm, elastic modulus of 195 kPa, and tearing energy of 1598 J/m 2 . Due to the reversible nature of physical interactions, polyHEAA-MA@Tween80 hydrogels can achieve fast stiffness/toughness recovery of 60%/33% without any external stimuli and resting time at room temperature. This work demonstrates a new design strategy to fabricate a new a singlenetwork hydrogel with high mechanical and self-recovery properties by incorporating both hydrophobic association and hydrogen bonds in the network, which may provide alternative viewpoint for the design of multifunctional tough hydrogels.

Synthesis of Poly(ε-caprolactone) Diacrylate for Micelle-Cross-Linked Sodium AMPS Hydrogel for Use as Controlled Drug Delivery Wound Dressing

“…Hydrophobic association is important for the formation of hydrogels with high strength and toughness. Generally, hydrophobic association hydrogels are prepared via micellar copolymerization that displays a network structure where micelles act as cross-linking agents to link between inner hydrophobic and external hydrophilic polymer chains . However, the simple physical cross-linking among the hydrophobic chains was quite weak, or its tensile strength was not high enough compared to that of the chemical cross-linking hydrogel.…”

“…Generally, hydrophobic association hydrogels are prepared via micellar copolymerization that displays a network structure where micelles act as cross-linking agents to link between inner hydrophobic and external hydrophilic polymer chains. 40 However, the simple physical cross-linking among the hydrophobic chains was quite weak, or its tensile strength was not high enough compared to that of the chemical cross-linking hydrogel. Therefore, a combination of chemical and physical cross-linking is commonly used to improve the mechanical properties of hydrogels.…”

Hydrogel: Diversity of Structures and Applications in Food Science

“…Hydrophobic association hydrogels (HA-gels) were firstly prepared by Liu et al [186] by using acrylamide (AAm) as a main component and octyl phenol polyethoxy ether as the hydrophobic segments. Due to their unique reversible, associative structure, excellent mechanical properties, and self-healing properties, [185,[187][188][189][190][191] HA-gels have been extensively studied during the past few decades. [191][192][193][194][195] Generally, HA-gels are prepared via micellar copolymerization (see Chemical crosslinking Section), which combines the water-soluble monomers with the hydrophobic monomer-containing micelles [196] .…”

“…HA-gels display a unique network structure, where the micelles act as physical crosslinking agents to associate with both the inner hydrophobic and external hydrophilic polymer chains. [185,189] When hydrogels are subjected to external forces, the dynamic crosslinking sites (micelles) disperse the stress and prevent the hydrogel from breaking, making HA-gels very suitable for use as self-healing hydrogels. Additionally, the hydrophobic molecular chains entangled within the micelles are unwound or slip to produce large amounts of dissipated energy, which greatly improves the toughness of the hydrogel.…”

Poly(l‐glutamic acid)‐based micellar hydrogel with improved mechanical performance and proteins loading

“…Many efforts have been made to promote the mechanical performance of hydrogels, including chemical–physical double networks and hydrophobic modified hydrogels that would form hydrophobic microdomains in networks to realize the stress consumption . Among these efforts, introduction of micelles, which undergo microscopic phase separation in aqueous environment, could consume the external loading to impart the hydrogels with higher resistance under big strain .…”