Thermoresponsive Hydrogels with Improved Actuation Function by Interconnected Microchannels

Abstract

Stimuli−responsive hydrogels are important in soft actuators research, as they change volume in response to environmental factors. Thermoresponsive hydrogels, such as poly(N‐isopropylacrylamide) (pNIPAM), typically have slow response rates and exert comparably weak forces, which usually limit their use as artificial muscles. Herein, it is shown that the incorporation of interconnected microchannels into the pNIPAM hydrogel by a template‐assisted approach leads to a significant increase in both the response rate and the volume change. For a microchannel density of only 5 vol%, a volume reduction of 90% is achieved, compared with only 12% for the bulk material, while material stiffness of the swollen hydrogels remains unchanged. By tailoring the channel density and the stiffness of the material, it is further possible to adjust the response rate and the exerted stroke force in an actuation setting. It is shown in a demonstrator gripper setup driven by the pNIPAM‐based artificial muscle that the performance of the gripper is strongly improved by the microengineered material compared with conventional bulk pNIPAM. The strategy of incorporating microchannels into the pNIPAM hydrogel provides a practical approach for the future use of volume phase transition‐based responsive materials in soft robotic applications.