Self-Healable, Tough, and Ultrastretchable Nanocomposite Hydrogels Based on Reversible Polyacrylamide/Montmorillonite Adsorption

Abstract

Nanocomposite hydrogels with unprecedented stretchability, toughness, and self-healing have been developed by in situ polymerization of acrylamide with the presence of exfoliated montmorillonite (MMT) layers as noncovalent cross-linkers. The exfoliated MMT clay nanoplatelets with high aspect ratios, as confirmed by transmission electron microscopy (TEM) and X-ray diffraction (XRD) results, are well dispersed in the polyacrylamide matrix. Strong polymer/MMT interaction was confirmed by Fourier transform infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC). The effective cross-link densities of these hydrogels are estimated in the range of 2.2-5.7 mol m(-3). Uniaxial tensile tests showed a very high fracture elongation up to 11 800% and a fracture toughness up to 10.1 MJ m(-3). Cyclic loading-unloading tests showed remarkable hysteresis, which indicates energy dissipation upon deformation. Residual strain after cyclic loadings could be recovered under mild conditions, with the recovery extent depending on clay content. A mechanism based on reversible desorption/adsorption of polymer chains on clay platelets surface is discussed. Finally, these nanocomposite hydrogels are demonstrated to fully heal by dry-reswell treatments.

Nanoclay Reinforced Self‐Cross‐Linking Poly(N‐Hydroxyethyl Acrylamide) Hydrogels with Integrated High Performances

“…However, conventional hydrogels, cross‐linked by chemical cross‐linkers, usually suffer from weak mechanical properties (i.e., poor mechanical strength, low stretchability, bad toughness, and/or low recoverability) owing to their heterogeneous network structures and lack of effective energy dissipation mechanisms, which largely limits their applications in the load‐bearing fields . In recent years, different strategies have been proposed to design high strength and tough hydrogels with novel microstructures, such as nanocomposite (NC) hydrogels, double network hydrogels, ionically cross‐linked hydrogels, hydrophobically associated hydrogels, and hydrogen bonds or dipole–dipole enhanced hydrogels …”

Hydrogels as a Replacement Material for Damaged Articular Hyaline Cartilage

“…The issue with these materials is the lack of fracture strength and elastic modulus that is required to support the expected load. There are several methods that have been developed to strengthen and toughen hydrogels, including doping with nano- or microparticles [108,109,110,111,112,113,114,115], weaved structured meshes [116], soft filling [117], polymer structure alignment [118], and polymer entanglement [119]. …”

“…Comparison of the tensile fracture stress and Young’s modulus of damaged human cartilage [148] with those of self-healing hydrogels, including PVA/PAAm [133], PAAm/Alginate (including various ionic strengths) [142,149], PAAm/MMT [111], PAMPSA [150], Polyampholytes [129], Carboxybetaine acrylamide [145], and Polyion complexes [130]. …”

Enhanced mechanical properties and self‐healing behavior of PNIPAM nanocomposite hydrogel by using POSS as a physical crosslinker

“…The aim of the above methods is to implement mechanisms for dissipating mechanical energy and maintaining high elasticity. Most inorganic fillers are one-dimensional nanoparticles, such as hectorite, 24,25 montmorillonite, 26 layered double hydroxide, 27 carbon nanotube, graphene oxide, [28][29][30][31] and titanate (IV) nanosheet. Among them, nanocomposite hydrogels (NC gels) have been paid more intention than the others, because they may combine the advantages of both inorganic and organic materials.…”