Hydrophobically modified nanocomposite hydrogels with self‐healing ability

Abstract

Several strategies have been developed in the past two decades to increase the mechanical performance of the hydrogels, and to generate self-healing function within the polymer network. Here, we combine two of these strategies to create hydrophobically modified nanocomposite (NC) hydrogels with high mechanical strength and self-healing efficiency. The hydrogels were prepared by in situ copolymerization of N,N-dimethylacrylamide and n-octadecyl acrylate (C18A) in the presence of 2 w/v % Laponite clay nanoparticles in an aqueous solution of worm-like sodium dodecyl sulfate micelles. Incorporation of hydrophobic C18A segments into the gel network significantly increases both the storage and loss moduli of NC hydrogels indicating increasing elasticity and energy dissipation. An improvement in the mechanical performance and self-recoverability of NC hydrogels was also observed after hydrophobic modification. The compressive fracture stress and Young's modulus increase with increasing amount of C18A, and they become 9 AE 1 MPa and 30 AE 2 kPa, respectively, at 4 mol % C18A. Incorporation of hydrophobic segments also provides a larger energy dissipation under large strain as compared to the traditional NC hydrogels providing a self-healing efficiency of 90 AE 10% in mechanically strong NC hydrogels.

Photocurable Methacrylated Silk Fibroin/Hyaluronic Acid Dual Macrocrosslinker System Generating Extracellular Matrix‐Inspired Tough and Stretchable Hydrogels

“…Cyclic tests provided the calculations of the hys-teresis energies (U hys ) and the energy dissipation coefficients (μ), which indicate the energy difference between the loading-unloading curves and the amount of the loading energy that dissipated, respectively. They were calculated by using the following equations [50] U hys = ∫ where 𝜖 max was equal to 60% in one-step cyclic tests, and it was 20%, 40%, 60%, and 80% in stepwise cyclic tests. Since it was found out that the U hys and μ do not change much with cycle number in one-step cyclic tests, their arithmetical average values were calculated, that is, U hys,avg and μ avg , respectively, in order to exhibit the effect of the DMAA concentration more clearly.…”

“…Cyclic tests provided the calculations of the hysteresis energies ( U hys ) and the energy dissipation coefficients ( µ ), which indicate the energy difference between the loading–unloading curves and the amount of the loading energy that dissipated, respectively. They were calculated by using the following equations [ 50 ] $$\begin{equation} {U}_{{\rm{hys}}} = \int_0^{{\varepsilon }_{{\rm{max}}}} {\sigma }_{{\rm{nom}}}{\rm{d}}\varepsilon - \int_{{\varepsilon }_{{\rm{max}}}}^0 {\sigma }_{{\rm{nom}}}{\rm{d}}\varepsilon \end{equation}$$ $$\begin{equation}\mu = \frac{{{U}_{{\rm{hys}}}}}{{\mathop \smallint \nolimits_0^{{\varepsilon }_{{\rm{max}}}} {\sigma }_{{\rm{nom}}}{\rm{d}}\varepsilon }}\end{equation}$$where ε max was equal to 60% in one‐step cyclic tests, and it was 20%, 40%, 60%, and 80% in stepwise cyclic tests. Since it was found out that the U hys and µ do not change much with cycle number in one‐step cyclic tests, their arithmetical average values were calculated, that is, U hys , avg and µ avg , respectively, in order to exhibit the effect of the DMAA concentration more clearly.…”

Dual Physically Cross‐Linked Hydrogels Incorporating Hydrophobic Interactions with Promising Repairability and Ultrahigh Elongation

“…[9] To achieve high mechanical properties, acrylamide-based materials as promising candidates have been widely utilized to synthesize the hydrogels with fairly high toughness. [10] Hu et al designed a DPC hydrogel by creating the first cross-linking through hydrogen bonding between clay nanosheets and poly(acrylamide-co-acrylic acid), and the secondary cross-linking by ionic coordination between Fe 3+ and COO groups of Pam-co-Ac polymer chains, which exhibited the great mechanical properties (3.5 MPa and 2100% elongation). [11] Hydrogel with elongation of 1000-1600% and tensile strength of 500 kPa has been synthesized from N,N-dimethylacrylamide (DMAc) and 2-(N-ethylperfluorooctane sulfonamido)ethyl acrylate (FOSA), resulting from physical crosslinks by core-shell nanodomains due to strong hydrophobic association of the FOSA moieties in water.…”

Highly tough and rapid self-healing dual-physical crosslinking poly(DMAA-co-AM) hydrogel

“…However, conventional chemically crosslinked hydrogels are always brittle and exhibit poor mechanical performance due to the absence of an energy dissipation mechanism, limiting their widespread applications. [27][28][29][30] Functional biomimetic self-healing hydrogels possess remarkable performance, such as fast self-healing properties and high mechanical strength and toughness, which greatly extend their service life, especially in articial e-skins, biosensing, and drug delivery. [31][32][33][34][35] Different approaches for repairing the damaged network structures of hydrogels have been explored to obtain highly self-healing hydrogels.…”