Quantifying the bending of bilayer temperature-sensitive hydrogels

Abstract

Stimuli-responsive hydrogels can serve as manipulators, including grippers, sensors, etc., where structures can undergo significant bending. Here, a finite-deformation theory is developed to quantify the evolution of the curvature of bilayer temperature-sensitive hydrogels when subjected to a temperature change. Analysis of the theory indicates that there is an optimal thickness ratio to acquire the largest curvature in the bilayer and also suggests that the sign or the magnitude of the curvature can be significantly affected by pre-stretches or small pores in the bilayer. This study may provide important guidelines in fabricating temperature-responsive bilayers with desirable mechanical performance.

Progress in the Field of Water‐ and/or Temperature‐Triggered Polymer Actuators

“…investigated the evolution of the curvature of bilayer temperature‐responsive hydrogels made of poly( N ‐isopropylacrylamide) (PNIPAM) with temperature changes based on a new mechanics theory. According to the theory, the largest curvature requires an optimal thickness ratio . Recently, Yarin et al.…”

“…This effect was achieved by producing hinges at appropriate places by printing black toner (light absorber) and exposing the entire printed film to IR light ( Figure 5). Black toner absorbs IR light and converts it to thermal energy, Polyacrylamide [40] Poly(acrylic acid) [55] Poly(sodium acrylate) [8] Poly(vinyl alcohol) [16] Polystyrene [6,17,49] Polydimethylsiloxane [18,25] Polycarbonate [19,20] Poly(N-isopropylacrylamide) [20,31,32,40,41,[43][44][45]49,50,52,60,[62][63][64][65][66]73,77] Poly(ethylene glycol) methacrylate [37] Chitosan [37] Poly(hydroxyethyl acrylamide) [46] (Continued ) raising the local temperature. Therefore, the PS directly underneath the black toner will be heated above its T g , relaxing stresses at that particular area and hence leading to bendingtype actuation.…”

“…According to the theory, the largest curvature requires an optimal thickness ratio. [31] Recently, Yarin et al explained the buckling of hydrogel bilayers based on the basic dynamics equations of hydrogel swelling/shrinkage phenomena. [32] A very interesting concept for making artificial swimmers that are also helpful in robotics is based on the local density variation upon changes in temperature.…”

Light-Responsive Soft Actuators: Mechanism, Materials, Fabrication, and Applications

“…With the rapid development of technology, intelligent, responsive actuators have been increasingly applied to engineering and daily life as a kind of material that can convert the energy contained in chemical or physical stimuli into macroscopic deformation [1]. These intelligent responsive actuators can be actuated by pH [2][3][4][5][6][7], gas [8][9][10], temperature [11][12][13][14], and other external stimuli, such as light [15,16], electric field, and magnetic field [17][18][19][20]. They have attracted the attention of researchers and have been a popular research topic in innovative materials science because of their high softness, multi-function, and other unique mechanical characteristics, such as easy modification, easy processing, and easy assembly [21,22].…”