Thermally Reversible Hydrogels

Responsive hydrogels are a type of soft material made up of lightly cross-linked polymers that are highly hydrophilic and have the ability to respond to stimuli. Thermally reversible hydrogels respond to a change in temperature and have the ability to exhibit either lower or upper critical solution temperatures where phase separation occurs. Self-oscillating hydrogels combine an oscillating chemical reaction with responsive hydrogels. In these gels chemical oscillations produced by the Belousov-Zhabotinsky (BZ) reaction lead to mechanical swell-deswell oscillations.  These materials have the potential to be used as soft actuators, microfluidic pumps, or as a form of chemical energy harvesting.  A primary objective for our project is to improve on existing self-oscillating gel systems by synthesizing a new self-oscillating hydrogel material that has the ability to be easily patterned. The patterning property that is being explored can then be used to create a large array of  synchronized oscillating gel patches, which in turn can be used to produce large cooperative and complex motion. Thermal reversibility makes printing gels more controllable because the polymer solutions exhibit phase separation leading to gelation under certain conditions. A copolymer composed of acrylic acid and N-isopropylacrylamide was synthesized and successfully displayed gelation above 35°C. A copolymer that displayed a gelation below 25°C was also synthesized by a reaction of poly(allylamine) and potassium cyanate. The next step will be to chemically crosslink the gel to make it permanent and incorporate the metal catalyst for the BZ reaction.