Dually-dynamic covalent tetraPEG hydrogels end-linked with boronate ester and acylhydrazone groups.

Well-defined dually dynamic hydrogels were prepared by end-linking four-armed poly(ethylene glycol) stars (tetraPEG stars) through two different types of dynamic covalent cross-links, boronates and acylhydrazones, leading to robust, self-healable materials. This required the prior end-functionalization of tetraPEG stars, originally bearing four hydroxyl terminal groups, with glucoronate, acylhydrazide and benzaldehyde groups, resulting in three differently end-functional star polymers. A first type of dually dynamic hydrogel resulted from the combination of the first two differently end-functionalized tetraPEG stars, cross-linked by 4-formylphenyl boronic acid, a small molecule bearing both an aldehyde and a boronic acid group, respectively complementary to the acylhydrazide and glucoronate end-groups of the two above-mentioned tetraPEG stars.