A Shape Memory Acrylamide/DNA Hydrogel Exhibiting Switchable Dual pH-Responsiveness

Shape memory acrylamide/DNA hydrogels include two different crosslinkers as stabilizing elements. The triggered dissociation of one of the crosslinking elements transforms the shaped hydrogel into an arbitrarily shaped (or shapeless) quasi-liquid state. The remaining crosslinking element, present in the quasi-liquid, provides an internal memory that restores the original shaped hydrogel upon the stimulus-triggered regeneration of the second crosslinking element. Two pH-sensitive shape memory hydrogels, forming Hoogsten-type triplex DNA structures, are described. In one system, the shaped hydrogel is stabilized at pH = 7.0 by two different duplex crosslinkers, and the transition of the hydrogel into the shapeless quasi-liquid proceeds at pH = 5.0 by separating one of the crosslinking units into a protonated cytosine-guanine-cytosine (C-G·C⁺) triplex. The second shaped hydrogel is stabilized at pH = 7.0, by cooperative duplex and thymine-adenine-thymine triplex (T-A·T) bridges. At pH = 10.0, the triplex units separate, leading to the dissociation of the hydrogel into the quasi-liquid state. The cyclic, pH-stimulated transitions of the two systems between shaped hydrogels and shapeless states are demonstrated. Integrating the two hydrogels into a shaped "two-arrowhead" hybrid structure allows the pH-stimulated cyclic transitions of addressable domains of the hybrid between shaped and quasi-liquid states.