Polyampholyte Hydrogels with pH Modulated Shape Memory and Spontaneous Actuation

Abstract

Polyampholyte hydrogels are synthesized by one-step copolymerization of cationic monomer 3-(methacryloylamino)propyltrimethylammonium chloride, anionic monomers sodium p-styrenesulfonate (NaSS), and methacrylic acid (MAA) without chemical crosslinker and adding salts. The hydrogels exhibit pH responsive shape memory behavior; the temporary shape of the hydrogel is formed manually after immersing in NaOH solution and fixed in HCl solution, while the shape recovery occurs by immersing in NaOH again. Most interestingly, the hydrogel shows a spontaneous shape change after the first shape memory cycle. When the recovered hydrogel with a little residual deformation is immersed in HCl again, it twists spontaneously and rapidly to the previous temporary shape. The spontaneous twisting and recovering can be repeated for ten times. Furthermore, the hydrogel swells quickly and is strengthened in HCl, while shrinks and weakens in NaOH during the shape change procedure. This unique synergistic effect of fast swelling, residual helical deformation, and increased strength plays a significant role in the spontaneous shape alternation. This new finding will initiate a new prosperous design for new soft actuators requiring successive actions.

3D Printing of Hydrogel Architectures with Complex and Controllable Shape Deformation

“…For example, the strip with the width ≈3.0 mm, thickness ≈0.3 mm, and 45° inclined grooves can twist to 700° in 52 s (Figure d, red), while that with width ≈1.5 mm, thickness ≈0.2 mm, and 45° inclined grooves twisted to over ≈1800° in ≈12 s (Figure e, black). These can be attributed to the increased thickness, width, or inclined angle, which lead to a larger deformation resistance and thereafter a decreased twisting rate . Furthermore, it can be also observed that at the beginning, the twisting angle was almost independent, whereas with the increasing of twisted angle, it became dependent (Figure d–f).…”

“…For the measurement of the bending and twisting angle, the deformed morphologies were recorded by a digital camera, and then these images were imported into Solidworks to character the bending/twisting angle in quantitative (Figure S12, Supporting Information). The twisting angle θ = 360° represented that the strip was twisted for one circle . In addition, the recovered angle in Figure d was defined as the difference between the angle at completely bent state and the bending angle at the time t .…”

Encoding Smart Microjoints for Microcrawlers with Enhanced Locomotion

“…Material is crucial for the design of microrobots, which regulates their mechanical properties and further determines their functions. Smart materials, which can sense and react to external stimuli, such as temperature, pH, light, humidity, magnetism, and electric fields, are indispensable for fabricating untethered soft microrobots. However, almost all stimuli–response materials reported exclusively exhibit a monotonic dependence of swelling deformation with some specific stimulus.…”

Laser Programmable Patterning of RGO/GO Janus Paper for Multiresponsive Actuators

“…Actuators that can deform reversibly under external stimuli (e.g., light, humidity, heat, pH value, chemicals, and magnetic/electric fields) are promising for cutting‐edge applications including artificial muscles, soft robotics, micro‐electromechanical systems (MEMS), and lab‐on‐a‐chip (LoC) systems . Generally, actuators can be produced based on either intrinsic smart materials or stimuli‐responsive multilayers.…”