  Hydrogels are soft materials engineered to suit a multitude of applications
that exploit their tunable mechanochemical properties. Dynamic hydrogels
employing noncovalent, physically crosslinked networks dominated by either
enthalpic or entropic interactions enable unique rheological and
stimuli-responsive characteristics. In contrast to enthalpy-driven interactions
that soften with increasing temperature, entropic interactions result in
largely temperature-independent mechanical properties. By engineering
interfacial polymer-particle interactions, we can induce a dynamic-to-covalent
transition in entropic hydrogels that leads to biomimetic non-ergodic aging in
the microstructure without altering the network mesh size. This transition is
tuned by varying temperature and formulation conditions such as $p$H, which
allows for multivalent tunability in properties. These hydrogels can thus be
designed to exhibit either temperature-independent metastable dynamic
crosslinking or time-dependent stiffening based on formulation and storage
conditions, all while maintaining strucutural features critical for controlling
mass transport, akin to many biological tissues. Such robust materials with
versatile and adaptable properties can be utilized in applications such as
wildfire suppression, surgical adhesives, and depot-forming injectable drug
delivery systems.
