Healable, Stable and Stiff Hydrogels: Combining Conflicting Properties Using Dynamic and Selective Three‐Component Recognition with Reinforcing Cellulose Nanorods

Abstract

Nanocomposite hydrogels are prepared combining polymer brush‐modified ‘hard’ cellulose nanocrystals (CNC) and ‘soft’ polymeric domains, and bound together by cucurbit[8]uril (CB[8]) supramolecular crosslinks, which allow dynamic host–guest interactions as well as selective and simultaneous binding of two guests, i.e., methyl viologen (the first guest) and naphthyl units (the second guest). CNCs are mechanically strong colloidal rods with nanometer‐scale lateral dimensions, which are functionalized by surface‐initiated atom transfer radical polymerization to yield a dense set of methacrylate polymer brushes bearing naphthyl units. They can then be non‐covalently cross‐linked through simple addition of poly(vinyl alcohol) polymers containing pendant viologen units as well as CB[8]s in aqueous media. The resulting supramolecular nanocomposite hydrogels combine three important criteria: high storage modulus (G′ > 10 kPa), rapid sol–gel transition (<6 s), and rapid self‐healing even upon aging for several months, as driven by balanced colloidal reinforcement as well as the selectivity and dynamics of the CB[8] three‐component supramolecular interactions. Such a new combination of properties for stiff and self‐healing hydrogel materials suggests new approaches for advanced dynamic materials from renewable sources.

Self‐Healable Supramolecular Hydrogel Formed by Nor‐Seco‐Cucurbit[10]uril as a Supramolecular Crosslinker

“…[5] However, the recovery of the physical properties of the hydrogel was suppressed over time due to rapid passivation of the exposed ionic surfaces of the hydrogel with otherc ounter ions in an onspecific manner.M aterials crosslinked with specific high-affinity interactions would possess greatlyi mproved self-healing andd urability properties. [6] Cucurbit[n]urils (CB[n], n = 6-8, 10,14), af amily of pumpkinshaped macrocycle hostm olecules, have specific and strong bindinga ffinities to various guest molecules. [7,8] CB [8] accommodates two aromatic moieties (such as methylviologen (MV) and naphthyl( Np) units) in its cavity to form at ernary complex, which hasb een utilized as as upramolecular crosslinker to link MV-a nd Np-conjugated hydrophilic polymers together to form ah ydrogel.…”

“…[9] Another approacht op reparing robust hydrogels is to make hard-soft composite materials;f or example, as oft polymeri sl inked to a" hard" material such as nanocrystaline cellulose by CB [8]. [6] CB [6],a nother member of the CB[n]f amily,f orms as elective and stable 1:1h ost-guest complex with polyamines such as 1,6 diaminohexane (DAH) and spermine with high binding affinity in water (K a > 10 10 -10 12 m À1 ). [10] The stable CB [6]-based host-guest interactions were exploited as as upramolecular crosslinkert of orm ar obusts elf-assembling hydrogel by as imple mixingo fC B [6]conjugated hyaluronic acid with DAH-conjugated hyaluronic acid.…”

“…[6] CB [6],a nother member of the CB[n]f amily,f orms as elective and stable 1:1h ost-guest complex with polyamines such as 1,6 diaminohexane (DAH) and spermine with high binding affinity in water (K a > 10 10 -10 12 m À1 ). [10] The stable CB [6]-based host-guest interactions were exploited as as upramolecular crosslinkert of orm ar obusts elf-assembling hydrogel by as imple mixingo fC B [6]conjugated hyaluronic acid with DAH-conjugated hyaluronic acid. [11] Since this simple in situ-formed hydrogel showed robust physical properties and good biocompatibility,i tc ould be used to entrap live cells.…”

“…[11] Since this simple in situ-formed hydrogel showed robust physical properties and good biocompatibility,i tc ould be used to entrap live cells. The CB [6]-DAH-based hydrogels have been extensively utilized for various biological applications including 3D cell culture, [11] cell delivery, [12] and 3D cell printing. [13] However,t hese CB [6]-and CB[8]-based hydrogels were formed with at least two different hydrophilic polymers each with differentf unctionalities, which were synthesized by laboriousmultistep processes.…”

Supramolecular hydrogels cross-linked by preassembled host–guest PEG cross-linkers resist excessive, ultrafast, and non-resting cyclic compression

“…Meijer et al fabricated tough supramolecular hydrogels cross-linked by the H-bonds between selfcomplementary UPy units 13,14 . Scherman et al demonstrated the fabrication of supramolecular cross-linked hydrogels by the host-guest interactions of cucurbit [n] uril complexes [15][16][17] . In addition to their pioneering study on double-network hydrogels, Gong et al developed ionic bond-based polyampholyte hydrogels that possess excellent robustness and viscoelasticity 6,[18][19][20][21] .…”