Supramolecular Reinforcement of Polymer–Nanoparticle Hydrogels for Modular Materials Design

Abstract

Moldable hydrogels are increasingly used as injectable or extrudable materials in biomedical and industrial applications owing to their ability to flow under applied stress (shear‐thin) and reform a stable network (self‐heal). Nanoscale components can be added to dynamic polymer networks to modify their mechanical properties and broaden the scope of applications. Viscoelastic polymer–nanoparticle (PNP) hydrogels comprise a versatile and tunable class of dynamic nanocomposite materials that form via reversible interactions between polymer chains and nanoparticles. However, PNP hydrogel formation is restricted to specific interactions between select polymers and nanoparticles, resulting in a limited range of mechanical properties and constraining their utility. Here, a facile strategy to reinforce PNP hydrogels through the simple addition of α‐cyclodextrin (αCD) to the formulation is introduced. The formation of polypseudorotoxanes between αCD and the hydrogel components resulted in a drastic enhancement of the mechanical properties. Furthermore, supramolecular reinforcement of CD–PNP hydrogels enabled decoupling of the mechanical properties and material functionality. This allows for modular exchange of structural components from a library of functional polymers and nanoparticles. αCD supramolecular binding motifs are leveraged to form CD–PNP hydrogels with biopolymers for high‐fidelity 3D (bio)printing and drug delivery as well as with inorganic NPs to engineer magnetic or conductive materials.

Microgels react to force: mechanical properties, syntheses, and force-activated functions

“…Other supramolecular motifs that have been employed include, for example, the host-guest complexes of cyclodextrins with cholesterol, 110 adamantane, 111 ferrocene, 112,113 and even as polypseudorotaxanes. 114 The introduction of supramolecular bonds into network structures has proven that such bonds can act as sacrificial bonds 115 that dissipate mechanical energy. 116 Similarly, supramolecular bonds have recently been introduced alongside covalent crosslinks into microgels using (+)-catechin hydrate (+C) rendering them more resistant to shear forces than purely covalently crosslinked microgels.…”

“…Other supramolecular motifs that have been employed include, for example, the host–guest complexes of cyclodextrins with cholesterol, 110 adamantane, 111 ferrocene, 112,113 and even as polypseudorotaxanes. 114…”

Solvent Controls Nanoparticle Size during Nanoprecipitation by Limiting Block Copolymer Assembly

“…Polymeric nanoparticles (NPs) are increasingly applied as colloidal drug delivery systems and building blocks in advanced (bio)material design. 1 − 6 Efficient translation of NPs and NP-based materials into clinical and industrial products requires strict control over the physicochemical properties of the engineered colloids, including NP size. 7 − 11 Nanoprecipitation is a robust method to produce NPs from amphiphilic block copolymers.…”

Mechanically Resistant Poly(N‐vinylcaprolactam) Microgels with Sacrificial Supramolecular Catechin Hydrogen Bonds

“…So far the mechanical properties of μgels have been mainly studied either using rheology or atomic force microscopy (AFM). [ 15 , 16 , 17 , 18 , 19 ] While rheological studies provide insight into the viscoelastic behavior of the bulk dispersion, [ 20 , 21 ] AFM investigates the local gel topology and the stimulation‐induced modulation of the mechanical properties of surface‐anchored μgels. [ 22 , 23 , 24 ] However, shear‐induced molecular transformations during the shear process in dispersion have not been investigated.…”