One-Pot and One-Step Fabrication of Salt-Responsive Bilayer Hydrogels with 2D and 3D Shape Transformations

Abstract

Bilayer hydrogels are one of the most promising materials for use as soft actuators, artificial muscles, and soft robotic elements. Therefore, the development of new and simple methods for the fabrication of such hydrogels is of particular importance for both academic research and industrial applications. Herein, a facile, one-pot, and one-step methodology was used to prepare bilayer hydrogels. Specifically, several common monomers, including N-isopropyl acrylamide, acrylamide, and N-(2-hydroxyethyl)acrylamide, as well as two salt-responsive zwitterionic monomers, 3-(1-(4-vinylbenzyl)-1Himidazol-3-ium-3-yl)propane-1-sulfonate (VBIPS) and dimethyl-(4vinylphenyl)ammonium propane sulfonate (DVBAPS), were chosen and employed with different combinations and ratios to understand the formation and structural tunability of the bilayer hydrogels. The results indicated that a salt-responsive zwitterionic-enriched copolymer, which could precipitate from water, plays a dominant role in the formation of the bilayer structure and that the ratio between the common monomer and the zwitterionic monomer had a significant effect on the structure. Due to the salt-responsive properties of polyVBIPS and polyDVBAPS, the resultant bilayer hydrogels exhibited excellent bidirectional bending properties in response to the salt solution. With the optimal monomer pair and ratio determined, the bend of the hydrogel could be reversed from ∼−360 to ∼266°in response to a switch between water and a 1.0 M NaCl solution. Additionally, this method was further used to fabricate small-scaled patterns with structural and compositional distinction in two-dimensional hydrogel sheets. These two-dimensional hydrogel sheets exhibited complex and reversible three-dimensional shape transformations due to the different bending behaviors of the patterned hydrogel stripes under the action of an external stimulus. This work provides greater insight into the mechanism of the one-step, one-pot method fabrication of bilayer hydrogels, demonstrates the ability of this method for the preparation of small-scale patterns in hydrogel sheets to endow the complex with a three-dimensional shape transformation capability, and hopefully opens up a new pathway for the design and fabrication of smart hydrogels.

Conductive Adhesive and Antibacterial Zwitterionic Hydrogel Dressing for Therapy of Full-Thickness Skin Wounds

“…Acrylamide (AAm, 99.0%) and N,N′-Methylenebisacrylamide (MBAA, 97%) were purchased from Aladdin reagent Inc. (Shanghai), The detailed synthesis route of dimethyl-(4-vinylphenyl) ammonium propane sulfonate (SVBA) can be found in our previous report ( He et al, 2019 ; Yuan H et al, 2021 ). In this experiment, all purified water was obtained from a Millipore system with an electronic conductance of 18.2 MΩ cm.…”

“…In this work, we ingeniously introduce a new structural salt-responsive zwitterion poly[3-(dimethyl(4-vinylbenzyl) ammonium) propyl sulfonate] (SVBA) into the polyAAm network to extend the practical candidates for the field of wound healing. The nature of polySVBA chains previously already presented unique salt-responsive properties and was applied to bacterial release ( Zhang et al, 2018 ; Wu et al, 2019 ), selective oil/water separation ( Wang et al, 2020 ), and thermal-induced soft actuators ( He et al, 2019 ), etc. Interestingly, rigid aromatic backbone and sequential ionic interactions synergistically promote surface bonding, potential conductivity, matrix stretchability, and self-healing properties.…”

Controllable, Bidirectional Water/Organic Vapors Responsive Actuators Fabricated by One‐Step Thiol‐Ene Click Polymerization

“…These results indicated that the gradient compositional distribution of this asymmetric film is not determined by the different polymerization rate of monomers. [18,19] In order to go deeply into why bidirectional vapor-responsive with the opposite bending reaction can be achieved by the same method, we carefully reviewed all the factors that may influence the fabrication of film. It turned out that besides the P x B y formulations, the processing method of substrate, such as the employment of the untreated PP petri dishes or the one cleaned with lye, and even soaking time in the lye, could have a significant effect on the synthesizing of the asymmetric films.…”

“…However, a porous asymmetric film generally has a weak mechanical strength. [ 20 ] Therefore, how to achieve a film with the well‐balanced mechanical strength and stimulus–response speed is essentially important for the design of smart stimuli‐responsive materials. Nature is the greatest teacher and we learned from it that two apparently contradictory elements can still be coordinated and unified.…”

Effect of 3D Printing Parameters on Self‐Driven Deformation Characteristics of Intelligent Hydrogel Actuators

“…Prepared bilayer hydrogels realized bidirectional bending properties under the stimulation of the salt solution. [14] Gao and co-workers developed a kind of bilayer thermoresponsive hydrogel actuators with curling/uncurling deformation property on the base of two-step molding in situ polymerization, which achieved snap-buckling motivated jumping under the stimulation of temperature. [15] Molding method owned the advantages of high polymerization efficiency, which prepared the hydrogel actuators with high mechanical strength successfully.…”