Switchable bifunctional stimuli-triggered poly-N-isopropylacrylamide/DNA hydrogels

DNA-tethered poly-N-isopropylacrylamide copolymer chains, pNIPAM, that include nucleic acid tethers have been synthesized. They are capable of inducing pH-stimulated crosslinking of the chains by i-motif structures or to be bridged by Ag⁺ ions to form duplexes. The solutions of pNIPAM chains undergo crosslinking at pH 5.2 or in the presence of Ag⁺ ions to form hydrogels. The hydrogels reveal switchable hydrogel-to-solution transitions by the reversible crosslinking of the chains at pH 5.2 and the separation of the crosslinking units at pH 7.5, or by the Ag⁺ ion-stimulated crosslinking of the chains and the reverse dissolution of the hydrogel by the cysteamine-induced elimination of the Ag⁺ ions. The DNA-crosslinked hydrogels are thermosensitive and undergo reversible temperature-controlled hydrogel-to-solid transitions. The solid pNIPAM matrices are protected against the OH^- or cysteamine-stimulated dissociation to the respective polymer solutions.