<p>Design of materials with novel
sensitivities and smart behaviour is important for the development of smart
systems with automated responsiveness. We have recently reported the synthesis of
hydrogels, cross-linked by <i>N,N'</i>-diallyltartardiamide (DAT). The covalent
DAT-crosslinking points have vicinal diols which can be easily cleaved with
periodate, generating valuable a-oxo-aldehyde
functional groups, useful for further chemical modification. Based on those
findings, we envisioned that a self-healable hydrogel could be obtained by
incorporation of primary amino functional groups, from <a>2-aminoethyl
methacrylate </a>hydrochloride (AEMA), coexisting with DAT into the same
network. The a-oxo-aldehyde
groups generated after the reaction with periodate would arise in the immediate
environment of amine groups to form imine cross-links. For this purpose, DAT-crosslinked
hydrogels were synthesized and carefully characterized. The cleavage of
DAT-crosslinks with periodate promoted changes in the mechanical and swelling
properties of the materials. As expected, a self-healing behavior was observed,
based on the spontaneous formation of imine covalent bonds. In addition, we
surprisingly found a combination of fast vicinal diols cleavage and a low speed
self-crosslinking reaction by imine formation. Consequently, it was found a
time-window in which a periodate-treated polymer was obtained in a transient
liquid state, which can be exploited to choose the final shape of the material,
before automated gelling. The singular properties attained on these hydrogels
could be useful for developing sensors, actuators, among other smart systems.</p>
Doubly Dynamic Hydrogel Formed by Combining Boronate Ester and Acylhydrazone Bonds