Stimuli-Responsive Donor-Acceptor and DNA-Crosslinked Hydrogels: Application as Shape-Memory and Self-Healing Materials

Carboxymethyl cellulose (CMC) chains are functionalized with self-complementary nucleic acid tethers and electron donor or electron acceptor functionalities. The polymer chains crosslinked by the self-complementary duplex nucleic acids and the donor-acceptor complexes as bridging units, yield a stiff stimuli-responsive hydrogel. Upon the oxidation of the electron donor units, the donor-acceptor bridging units are separated, leading to a hydrogel of lower stiffness. By the cyclic oxidation and reduction of the donor units, the hydrogel is reversibly transformed across low and high stiffness states. The controlled stiffness properties of the hydrogel are used to develop shape-memory hydrogels. In addition, CMC hydrogels crosslinked by donor-acceptor complexes and K+-stabilized G-quadruplexes reveal stimuli-responsive properties that exhibit dually triggered stiffness functions. While the hydrogel bridged by the two crosslinking motifs reveals high stiffness, the redox-stimulated separation of the donor-acceptor complexes or the crown-ether-stimulated separation of the G-quadruplex bridges yields two alternative hydrogels exhibiting low stiffness states. The control over the stiffness properties of the dually triggered hydrogel is used to develop shape-memory hydrogels, where the donor-acceptor units or G-quadruplex bridges act as "memories", and to develop triggered self-healing process of the hydrogel.