Mechanoresponsive Metal‐Organic Cage‐Crosslinked Polymer Hydrogels

Abstract

We report the formation of metal‐organic cage‐crosslinked polymer hydrogels. To enable crosslinking of the cages and subsequent network formation, we used homodifunctionalized poly(ethylene glycol) (PEG) chains terminally substituted with bipyridines as ligands for the Pd6L4 corners. The encapsulation of guest molecules into supramolecular self‐assembled metal‐organic cage‐crosslinked hydrogels, as well as ultrasound‐induced disassembly of the cages with release of their cargo, is presented in addition to their characterization by nuclear magnetic resonance (NMR) techniques, rheology, and comprehensive small‐angle X‐ray scattering (SAXS) experiments. The constrained geometries simulating external force (CoGEF) method and barriers using a force‐modified potential energy surface (FMPES) suggest that the cage‐opening mechanism starts with the dissociation of one pyridine ligand at around 0.5 nN. We show the efficient sonochemical activation of the hydrogels HG3–6, increasing the non‐covalent guest‐loading of completely unmodified drugs available for release by a factor of ten in comparison to non‐crosslinked, star‐shaped assemblies in solution.

The network structure in transient telechelic polymer networks: extension of the Miller–Macosko model

“…Two series of papers by the Olsen and Johnson 14–16,51,56 and by Lang and his coworkers 45,57–59 which use numerical approaches to simulate the network structure and defects are two great candidates for further verification. Despite experimental studies on networks with systematic variation of junction functionality being scarce, some works, including those using MOCs 33,34,60–62 or nanoparticles 29–31 as networks junctions, include versatile junction functionalities but rather poorly defined. All topology switching networks are based on changing the junction functionality in response to external stimuli, which could be also studied.…”

Dynamic Cages—Towards Nanostructured Smart Materials

“…The ability of such gels to trap large numbers of molecules within the cavity of a cage makes them useful for applications that include drug delivery or catalysis. Furthermore, the dynamic nature of the linkages in these systems gives rise to useful 1DMs with self‐healing, shear thinning, mechanoresponsive, stimuli‐responsive, and many other properties [128–130] …”

Nested Non-covalent Interactions Expand the Functions of Supramolecular Polymer Networks

“…In searching for a material to demonstrate this idea, we recognized that such a configuration could be achieved with MOC-crosslinked polymers (polyMOCs). [23][24][25][26] MOCs are, in some cases, known to display pronounced host-guest binding ability, [27][28][29][30][31] and a few reports of polyMOCs have leveraged MOCs that can bind guest molecules [32][33][34][35] ; however, no studies have explored how the bulk properties of polyMOCs can be varied by altering guest binding thermodynamics, nor have they leveraged this unique nested junction structure to achieve functions that cannot be obtained with traditional supramolecular networks. For example, we imagined at least three functions that could potentially be uniquely achieved with nested polyMOC networks: (1) guest-induced manipulation of bulk stress-relaxation dynamics, wherein small molecule guests alter the metal-ligand coordination dynamics of the junction; (2) resistance to dissolution under off-stoichiometry network formation conditions or in the presence of competitive reagents due to synergistic stabilization of MOC junctions bound to guests; and (3) the ability to control both percolation (i.e., gelation) and dissolution using selective self-sorting of MOC junctions driven by guest recognition.…”