Covalent Network Formation Rate Controls Depletion-Induced Supramolecular Assembly in Hybrid Double Network Hydrogels

The introduction of a secondary covalent polymer network is a powerful approach to extend the usable application range of supramolecular hydrogels. While it is recognized that dramatic changes in mechanics can occur with their addition, there is a lack of insight into the impact of added covalent polymers on hydrogels with underlying supramolecular filament nanostructures. Here we show that through controlling the rate of covalent network formation by the inverse electron-demand Diels-Alder reaction, the mesoscale architecture of the supramolecular network can be programmed. Slow macromonomer crosslinking enables depletion-induced supramolecular assembly of the supramolecular filaments into bundles above a critical macromonomer concentration, whereas rapid covalent network formation halts this dynamic process by effectively locking in the low-nm scale supramolecular nanostructures. This kinetic difference further translates into mechanically distinct hydrogels, where slow-forming hybrid networks reveal a two-fold increase in toughness as compared to fast-crosslinked networks, thanks to the bundled supramolecular filaments. Through harnessing the macromolecular crowding capacity of reactive macromonomers and their reaction kinetics, a new axis to control the hierarchical structure of supramolecular hydrogels through depletion forces is unlocked that can be exploited to shape this soft matter class for numerous applications.