Actuation of Hydrogel Architectures Prepared by Electrophoretic Adhesion of Thermoresponsive Microgels

Abstract

Owing to their unique properties, hydrogels may be used for preparing soft actuators. Soft actuators are expected to respond quickly; however, the response speed of gels is slow. To study this issue and overcome it, thermoresponsive soft actuators were prepared by the electrophoretic adhesion of cationic and anionic thermoresponsive microgels, comprising poly(diallyldimethylammonium chloride) and poly(styrenesulfonate) sodium salt, respectively. The kinetics of the prepared hydrogel architectures in response to temperature depended on the microgel diameter instead of the architecture size. We also prepared bilayered hydrogel architectures by adhesion of thermoresponsive and/or nonthermoresponsive microgels. These bent rapidly in response to temperature because these architectures consisted of microgel assemblies. In addition, specific bending motion was demonstrated by the adhesion of microgel layers of different sizes. The present study provides not only a guideline for the design of hydrogel actuators with quick response but also presents a method for the free-form fabrication of functional hydrogel materials that undergo complex motions in response to stimuli.

Temporary Actuation of Bilayer Polymer Hydrogels Mediated by the Enzymatic Reaction

“…In the case of polymer hydrogels, it is the different swelling ratios of stimuliresponsive hydrogels under different circumstances that causes the deformational behaviors of the hydrogel actuators. 5,22,23 The most common way to achieve the bending of actuators is to construct an anisotropic structure, such as the bilayer structure. 13,24,25 For a bilayer hydrogel actuator, the shape change of the entire structure is usually caused by the different expanding/shrinking trends of each layer of the hydrogels under a certain stimulus.…”

“…Smart actuators constructed by stimuli-responsive polymers have deformational behaviors such as expansion and bending under specific stimuli such as light, − heat, − electricity, − and pH change. − They have wide application prospects in the fields of shape memory materials, , soft robotics, , artificial muscles, , microfluidics, , and drug delivery ,, and have attracted significant attentions. In the case of polymer hydrogels, it is the different swelling ratios of stimuli-responsive hydrogels under different circumstances that causes the deformational behaviors of the hydrogel actuators. ,, The most common way to achieve the bending of actuators is to construct an anisotropic structure, such as the bilayer structure. ,, For a bilayer hydrogel actuator, the shape change of the entire structure is usually caused by the different expanding/shrinking trends of each layer of the hydrogels under a certain stimulus. ,− Based on this principle, the hydrogel actuators normally exhibit a monotonic responsiveness, that is, there is only one response action after being stimulated once. To generate a multiple or cyclic response, it is usually necessary to provide multiple stimuli, which limits the development of stimuli-responsive hydrogels as a kind of smart actuators.…”

Nanocomposite Hydrogel Actuators with Ordered Structures: From Nanoscale Control to Macroscale Deformations

“…According to the Tanaka−Fillmore theory of transformative hydrogels, the swelling and deswelling rates of the hydrogel are proportional to the diffusion coefficient of the water inside the hydrogel and inversely proportional to the square of the minimum size of the hydrogel. [132] By minimizing the size of hydrogel actuators, such as microgels with micrometers or submicrometers, [133] Lee et al demonstrate a 3D micro hydrogel device capable of fast actuation via incorporating elastic instability, inspired by the inset-trapping action of Venus flytrap. [134] Owing to energy accumulation and instantaneous energy release, a micro hydrogel device with two legs curved with hydrogel plates jumped apace when applied with the solvent.…”

Ecofriendly Controlled-Release Insecticide Carrier: pH-/Temperature-Responsive Rosin-Derived Hydrogels for Avermectin Delivery against Mythimna separata (Walker)

“…Since the synthesis of the 2-hydroxyethyl methacrylate (HEMA) hydrogel by Wichterle and Lim in 1954, hydrogels have attracted attention because of their three-dimensional (3D) network structure and high hydrophilicity . The targeted distribution and delivery of intelligent responsive hydrogels as a representative soft matter are also important. − Because the temperature, an external stimulus, can be easily applied and optimized, poly­( N -isopropylacrylamide) (PNIPAM), a conventional temperature-responsive substance, is frequently used as a temperature-sensitive controlled-release carrier (i) as its low critical solution temperature (LCST) point is close to the environment temperature and (ii) for hydrophobic–hydrophilic conversion. In agriculture, controlled-release technology uses hydrogels as intelligent carriers for the delivery of insecticides and fertilizers for plant growth regulators and soil water retention. − …”