Hydrogels are hydrophilic polymer scaffolds surrounded by adsorbed water. From a dry state, they are capable of swelling in volume by up to two orders of magnitude – becoming up to 99% water - whilst still remaining solid (if a little squishy).

Responsive hydrogels lose this affinity for water – sometimes quite profoundly – when an environmental stimulus, such as temperature or pH, transitions beyond a critical value. Conformational changes in the scaffold squeeze the water out, and the gel shrivels dramatically. This volume change is reversible (albeit non-reciprocal), allowing for cycles of activation and deactivation. As such, responsive hydrogels have important and exciting applications in microscale actuators.

This talk will describe some of the big open areas of hydrogel modelling, before detailing two (very) recent unpublished theoretical pieces of work on 1) thermoresponsive displacement pumps for microfluidic devices, and 2) coupling pH-responsive gels to oscillating reactions to enable communication and synchronisation.