Photothermally driven fast responding photo-actuators fabricated with comb-type hydrogels and magnetite nanoparticles

Abstract

To overcome the slow kinetics of the volume phase transition of stimuli-responsive hydrogels as platforms for soft actuators, thermally responsive comb-type hydrogels were prepared using synthesized poly(N-isopropylacrylamide) macromonomers bearing graft chains. Fast responding light-responsive hydrogels were fabricated by combining a comb-type hydrogel matrix with photothermal magnetite nanoparticles (MNP). The MNPs dispersed in the matrix provide heat to stimulate the volume change of the hydrogel matrix by converting absorbed visible light to thermal energy. In this process, the comb-type hydrogel matrix exhibited a rapid response due to the free, mobile grafted chains. The comb-type hydrogel exhibited significantly enhanced light-induced volume shrinkage and rapid recovery. The comb-type hydrogels containing MNP were successfully used to fabricate a bilayer-type photo-actuator with fast bending motion.

Morphing in nature and beyond: a review of natural and synthetic shape-changing materials and mechanisms

“…They use these materials as heat-activated hinges attached to solid plates, and by varying the weight percentage of additives are able to adjust the response speed of petals opening on a model flower as a function of distance. Similar effects have been achieved by others using gold NP [155] and magnetite particles [109].…”

“…Response rate can be increased with the addition of microchannels [108], mimicking the operation of vasculature and allowing integration into microfluidic devices. Addition of graft chains, creating a comb-type hydrogel, has also been demonstrated to improve the response speed of some nanocomposites by around a factor of three [109].…”

“…Liquid crystal-based systems are wellknown for their light response, triggering the transisomer switch referred to earlier. For LCEs, polymer systems and hydrogels, the addition of nanoparticle composites with tuned plasmon resonances have been shown to add photo-response by triggering heating [109,152,153].…”

Computational investigation of magnetic hydrogels and elastomers

“…In addition, the time response of the single pH-sensitive hydrogel was relatively slow [4,18,102]. Although two strategies were proposed to improve the response rate, such as utilization of the macroporous hydrogel or multiple smaller hydrogel disks, the hydrogel suffers from low mechanical stiffness [4,14,107], making it inappropriate for dynamic control of the microfluidic flow with a wide range of patterns required by the microphysiological systems. Therefore, much effort was made to investigate the magnetic-sensitive hydrogel as microfluidic controller [108][109][110][111].…”

“…It is further found from Figure 4.10(b) that, the hydrogel swells during its motion, due to the diffusion of the fluid. In order to elucidate the swelling phenomenon, the time evolutions 107 of the average volume swelling ratios are demonstrated in Figure 4.10(d), where the three curves have the similar profile patterns. The hydrogels swell sharply at the early stage of swelling, and then its rate decreases smoothly.…”