Rapid Accessible Fabrication and Engineering of Bilayered Hydrogels: Revisiting the Cross-Linking Effect on Superabsorbent Poly(acrylic acid)

Abstract

Superabsorbent hydrogels are significant not only in materials science but also in industries and daily life, being used in diapers or soil conditioners as typical examples. The main feature of these materials is their capacity to hold considerable amount of water, which is strongly dependent on the cross-linking density. This study focuses on the preparation of hydrogels by reweighing the effect of cross-linking density on physical properties, which provides green fabrication of bilayered hydrogels that consist of homogeneous structural motifs but show programmed responses via sequential radical polymerization. In particular, when two hydrogel layers containing different cross-linking densities are joined together, an integrated linear bilayer shows heterogeneous deformation triggered by water. We monitor the linear hydrogel bilayer bending into a circle and engineer it by incorporating disperse dyes, changing colors as well as physical properties. In addition, we demonstrate an electric circuit switch using a patterned hydrogel. Anisotropic shape change of the polyelectrolyte switch closes an open circuit and lights a light-emitting diode in red. This proposed fabrication and engineering can be expanded to other superabsorbent systems and create smart responses in cross-linked systems for biomedical or environmental applications.

Recent Progress on Molecular Photoacoustic Imaging with Carbon-Based Nanocomposites

“…We anticipate that the imaging techniques and the contrast agents described will be further developed into more advanced materials and to monitor or manipulate them using the PA signals generated from the materials [ 124 , 125 ]. Therefore, on the one hand, the agent materials can be incorporated into biocompatible polymers such as hydrogels or bio-based thermosets, to enhance sensing ability as a signal transducer for PA signals under physiological conditions [ 123 , 124 , 125 , 126 , 127 , 128 , 129 , 130 , 131 , 132 ]. On the other hand, they would provide spatiotemporal control of stimuli-responsive materials that exhibit auto-inductive or reversible responses [ 133 , 134 , 135 , 136 , 137 , 138 ] or would be used to analyze interior structures when embedded in complex materials containing biomimetic or hierarchical structures [ 104 , 117 , 139 , 140 , 141 ].…”

Recent Progress on Near-Infrared Photoacoustic Imaging: Imaging Modality and Organic Semiconducting Agents

“…Additionally, self-propagating reactions, such as self-assembly or triggered head-to-tail depolymerization [114,115,116,117,118], can readily turn on–off or even amplify the PA signal. Furthermore, addition of the PA properties to various network materials, such as porous materials or hydrogels [119,120,121,122,123,124,125,126], can provide a non-destructible in situ monitoring system or facile, selective manipulation of physical properties of the networks in response to NIR.…”

Chemical Design of Functional Polymer Structures for Biosensors: From Nanoscale to Macroscale

“…When swelling, the hydrogel bilayer bent in water because of subtle differences in the cross-linking density, which was markedly dependent on the pH. Furthermore, the bilayered material was used as an underwater electronic circuit switch ( Figure 22 ) [ 130 ]. These kinds of materials have the potential for autonomous, biomimetic applications, where materials are required to not only recognize changes in the surroundings but also provide feedback and adapt themselves to the new environment.…”