Single and Bi-Layer Polyacrylamide Hydrogel-Based Microcapsules for the Triggered Release of Loads, Logic Gate Operations and Intercommunication Between Microcapsules.

A method to assemble loaded stimuli-responsive DNA-polyacrylamide hydrogel-stabilized microcapsules is presented. The method involves the coating of substrate-loaded CaCO3 microparticles, functionalized with nucleic acid promoter units, and the crosslinking of DNA-modified polyacrylamide chains, on the microcapsules, using the hybridization chain reaction (HCR), to yield the DNA-crosslinked hydrogel coating. Dissolution of the CaCO3 particles generated the substrate-loaded hydrogel protected microcapsules. The microcapsule-hydrogel shells include engineered stimuli-responsive oligonucleotides crosslinkers that control the stiffness of the hydrogel shells, allowing the triggered release of the loads. One approach includes the incorporation of cofactor-dependent DNAzyme units into the crosslinked hydrogel layer (cofactor = Mg2+-ions, Zn2+-ions or histidine) as stimuli-responsive units. Cleavage of the crosslinking DNAzyme substrates by the respective cofactors yields hydrogel coatings of reduced stiffness and higher porosity, that allows the release of the loads. A further approach has involved the application of the HCR process to assemble the bi-layer hydrogel microcapsules being unlocked by two cooperative triggers. Bi-layer microcapsules consisting of a K+-ions stabilized G-quadruplex/18-crown-6-ether responsive layer and a Mg2+-ion DNAzyme responsive layer is presented. Unlocking and locking of the G-quadruplex crosslinked layer by 18-crown-6-ether and K+-ions, respectively, and in the presence of Mg2+-ions, allows switchable controlled release of the load. In addition, the intercommunication of two kinds of stimuli-responsive bi-layer hydrogel microcapsules carrying two different loads (Tetramethylrhodamine-dextran, TMR-D, and CdSe/ZnS quantum dots) is demonstrated. The intercommunication process involves the stimuli-triggered generation of "information transfer" strands from one microcapsule to another that activate the release of the loads.