Double‐crosslinked reversible redox‐responsive hydrogels based on disulfide–thiol interchange

Abstract

We present novel redox‐responsive hydrogels based on poly(N‐isopropylacrylamide) or poly(acrylamide), consisting of a reversible disulfide crosslinking agent N,N′‐bis(acryloyl)cystamine and a permanent crosslinking agent N,N′‐methylenebisacrylamide for microfluidic applications. The mechanism of swelling/deswelling behavior starts with the cleavage and reformation of disulfide bonds, leading to a change of crosslinking density and crosslinking points. Raman and ultraviolet‐visible spectroscopy confirm that conversion efficiency of thiol–disulfide interchange up to 99%. Rheological analysis reveals that the E modulus of hydrogel is dependent on the crosslinking density and can be repeatedly manipulated between high‐ and low‐stiffness states over at least 5 cycles without significant decrease. Kinetic studies showed that the mechanical strength of the gels changes as the redox reaction proceeds. This process is much faster than the autonomous diffusion in the hydrogel. Moreover, cooperative diffusion coefficient (Dcoop) indicates that the swelling process of the hydrogel is affected by the reduction reaction. Finally, this reversibly switchable redox behavior of bulky hydrogel could be proven in microstructured hydrogel dots through short‐term photopatterning process. These hydrogel dots on glass substrates also showed the desired short response time on cyclic swelling and shrinking processes known from downsized hydrogel shapes. Such stimuli‐responsive hydrogels with redox‐sensitive crosslinkers open a new pathway in exchanging analytes for sensing and separating in microfluidics applications. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 2590–2601

Pathway Dependence in Redox‐Driven Metal–Organic Gels

“…Redox responses make the gel systems desirable for biomimicry, as well as for numerous possible applications . However, most of the redox‐fuelled gels found in the literature are polymeric in nature and are usually developed from the intermolecular disulfide exchange reaction‐based molecular systems . Therefore, designing and construction of new supramolecular low molecular weight redox‐based gels is highly desirable; these are expected to have very different underlying properties …”

“…Herein, we designed a new redox‐responsive metal–organic hydrogel system and discuss the pathway dependence of these redox‐based gels (Figure ). Unlike other redox systems, instead of using sulfide/disulfide‐based ligands, herein, we utilize dynamic imine bond formation between an aldehyde ( 1 ) and an amine ( 2 ) as the key chemical reaction to synthesize the ligand ( 3 ). To make the organic framework redox responsive, we incorporated Fe II ions into the gel medium.…”

Dynamic, multimodal hydrogel actuators using porphyrin-based visible light photoredox catalysis in a thermoresponsive polymer network

“…[12][13][14] Oen, the responsivity is programmed into the so material at the (macro)molecular level prior to formation of a liquid crystal elastomer or gel network for example. Some common external stimuli that have been investigated previously include changes in pH [15][16][17] or temperature, [18][19][20] reduction and oxidation, [21][22][23][24] magnetic elds, 25 or irradiation with light (e.g., UV, visible, near-IR (NIR)), [26][27][28][29][30][31][32][33][34][35][36][37] where the selection of a material's responsive components is typically based on the desired application and preference for a specic external stimulus.…”

Dynamic, Multimodal Hydrogel Actuators Using Porphyrin-Based Visible Light Photoredox Catalysis in a Thermoresponsive Polymer Network

“…[12][13][14] Often, the responsivity is programmed into the soft material at the (macro)molecular level prior to formation of a liquid crystal elastomer or gel network for example. Some common external stimuli that have been investigated previously include changes in pH [15][16][17] or temperature, [18][19][20] reduction and oxidation, [21][22][23][24] magnetic fields, 25 or irradiation with light (e.g., UV, visible, near-IR (NIR)), [26][27][28][29][30][31][32][33][34][35][36][37] where the selection of a material's responsive components is typically based on the desired application and preference for a specific external stimulus.…”