Fabrication of soft, stimulus-responsive structures with sub-micron resolution via two-photon polymerization of poly(ionic liquid)s

Soft, stimulus-responsive 3D structures created from crosslinked poly(ionic liquid)s (PILs) have been fabricated at unprecedented sub-micron resolution by direct laser writing (DLW). These structures absorb considerable quantities of solvent (e.g., water, alcohol, and acetone) to produce PIL hydrogels that exhibit stimulus-responsive behavior. Due to their flexibility and soft, responsive nature, these structures are much more akin to biological systems than the conventional, highly crosslinked, rigid structures typically produced using 2-photon polymerization (2-PP). These PIL gels expand/contract due to solvent uptake/release, and, by exploiting inherited properties of the ionic liquid monomer (ILM), thermo-responsive gels that exhibit reversible area change (30 +/- 3%, n = 40) when the temperature is raised from 20 degrees C to 70 degrees C can be created. The effect is very rapid, with the response indistinguishable from the microcontroller heating rate of 7.4 degrees C s(-1). The presence of an endoskeletonlike framework within these structures influences movement arising from expansion/contraction and assists the retention of structural integrity during actuation cycling.