Experiment / Wet

The study utilized a PDMS (polydimethylsiloxane) droplet microfluidic device with a flow-focusing junction to generate uniform water-in-oil droplets. The aqueous phase contained specifically designed DNA strands capable of forming X-shaped Holliday junctions with sticky ends, suspended in a 1x Tris-EDTA buffer (pH 8.0) supplemented with 150 mM NaCl and EvaGreen dye. Gelation was achieved by incubating the microdroplets at 95 °C and subsequently cooling them to 20 °C at a controlled rate of 0.1 °C/min using a thermocycler. This thermal process allowed the DNA strands to self-assemble into 3D hydrogel networks within the 30–60 μm discrete droplets.

The researchers successfully fabricated monodisperse DNA hydrogel microbeads. They demonstrated that these microbeads could undergo targeted dissolution via toehold-mediated strand displacement upon the addition of specific complementary DNA strands. Furthermore, by incorporating a structural “hairpin bridge” between the DNA motifs, they achieved reversible morphological manipulation. The sequential addition of “extender” and “shrinker” DNA strands allowed the microbeads to predictably swell (increasing the internal structural distance from ~26 nm to ~45 nm) and shrink on-the-fly. Additionally, the team successfully executed a complex molecular computing primitive—a “Winner-Takes-All” competition—between two distinct populations of gel beads.