DNA PROGRAMMABLE SOFT MATTER DEVICES
Cangialosi, Angelo J.
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The ability to program soft materials to undergo observable shape transformations in response to environmental stimuli is critical to the development soft programmable matter. In recent years, chemomechanical shape-changing hydrogels have garnered interest because they do not require wires or batteries and can operate untethered at smaller size scales. Devices comprised of these materials can respond to only a limited set of spatially non-specific stimuli such as temperature or pH - and are therefore restricted to a small set of final states. On the other hand, due to the large sequence space and programmable interactions of DNA molecules, devices comprised of DNA-conjugated hydrogel domains can potentially access a much larger set of final configurations through sequence-specific, addressable actuation of individual domains. To investigate the shape-changing properties of single domain DNA-conjugated hydrogels, we first determine the swelling extent of DNA-crosslinked acrylamide networks in response to sequence-specific DNA stimuli. By coupling the DNA crosslinks to a DNA hybridization chain reaction that enables further incorporation of DNA to the crosslink sites, we demonstrate that specific DNA molecules can induce up to 100-fold volumetric hydrogel expansion. This large degree of swelling is then used to actuate approximately centimeter-sized gels containing multiple DNA-sensitive gel domains that each change shape in response to different DNA sequences. From swelling experiments and finite-element simulations we develop a simple design rule for the DNA-controlled shape change of a hydrogel bilayer. The next generation of soft programmable matter and robotics will require materials that not only respond to distinct chemical species, but mechanical forces as well. Prior work in developing mechanochemically responsive polymers makes use of mechanophores - molecules that change configuration and initiate chemical reactions in response to mechanical forces - to instill bulk materials with force sensing properties. In this work, we use established thermodynamic models to design two DNA mechanophore complexes capable of responding to two distinct ranges of applied force. We micromold PEGDA copolymer hydrogels containing DNA mechanophore complexes and examine the force-sensing properties of the bulk material through the use of a multifunctional force microscope and a DNA-based fluorescence reporting scheme. Because DNA molecules can be coupled to molecular sensors, amplifiers, and logic circuits, the incorporation of DNA complexes into hydrogel networks - whether as mechanophores or chemical crosslinkers -introduces the possibility of building soft matter devices that respond to numerous, distinct inputs and autonomously implement chemical control programs. These soft matter constructs have the potential to exhibit the multistage, goal-directed behaviors that are currently impossible to achieve in other soft robotic devices.