Hydrogels derived from metal-ligand association have shown promise as biomimetic self-healing materials.  Current limitations of these systems include their relatively poor mechanical properties and narrow functional scope.  We wondered if it would be possible to combine metal-ligand association with metallosupramolecular self-assembly to induce a hierarchical gelation process that would lead to novel materials with enhanced properties and well-defined porous structures for encapsulation of small molecules.   This talk will discuss a novel class of hydrogels prepared via coordination-based self-assembly of Pd(II) ions with dipyridine-terminated  poly(ethylene glycol) (PEG) macromers (1 ).  These materials lead to hydrogels wherein the junctions are uniform hollow nanoscopic �Fujita spheres� (Figure 1).  The dynamic nature of the self-assembly derived from the relatively weak pyridine-Pd(II) coordination bonds was expected to allow the network to flow under high rates of shear stress and subsequently to heal.  Meanwhile, the large number of coordination bonds formed at each junction makes the network mechanically robust.The chemical, structural, rheological, and thermodynamic characterization of our novel suprametallogels and the mechanism through which they form will be described. Control over macroscopic gel properties (e.g., storage modulus) through variation parameters including gel concentration, length of PEG chains, and source of Pd(II) ions will be discussed.  Lastly, the network spheres can be employed as vectors for delivery of biologically-relevant materials.  For instance, the spheres can encapsulate and then steadily release doxorubicin, a widely used chemotherapeutic agent.

Suprametallogels based on Fujita sphere self-assembly

248th National Meeting (2014)

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