Microfluidic Janus fibers with dual thermoresponsive behavior for thermoactuation

Abstract

Thermoresponsive bilayer hydrogels have gained attention due to their fast response time and excellent recovery. A side-by-side capillary-based microfluidic device has been used to produce thermoresponsive Janus fibers by photopolymerization of monomer streams. These fibers had one of their parts consisting in a thermoresponsive polymer obtained from oligo(ethylene glycol) acrylate, 2-ethoxyethyl acrylate, and poly(ethylene glycol) diacrylate, while the other one consisted in a non-thermoresponsive polymer. The fibers showed reversible coiling and uncoiling phenomena with two temperature transitions upon heating (and cooling). The unexpected dual thermoresponsiveness was investigated by screening a wide range of parameters including the nature of the photoinitiator and comonomers. The transition temperatures were tuned from 0 to 80 °C by varying the comonomer composition, but also the nature and concentration of the crosslinker used. The ability of these Janus fibers to act as thermally-triggered actuators was demonstrated by performing up to four heating–cooling cycles and attaching a small weight at one of the extremities of the fiber. These results pave the way to the development of easily tunable polymer-based fibrous thermoactuators.