Redox- and Photo-Responsive Fe ^3+/2+ -Cross-Linked Carboxymethyl Cellulose Methacrylate Dissipative Gels: Synthesis and Applications

High Resolution Image Download MS PowerPoint Slide The synthesis of redox-active Fe 3+ -cross-linked carboxymethyl cellulose methacrylate cryogels ( Fe 3+ -CMCMA ), revealing switchable, transient, dissipative stiffness properties, is introduced. The switchable, transient functions are triggered by ascorbate-mediated reduction of the high-stiffness gel to the lower-stiffness Fe 2+ -CMCMA gel, and the concomitant aerobic oxidation of the Fe 2+ -CMCMA to the Fe 3+ -CMCMA gel state. Alternatively, integration of native photosynthetic photosystem-I ( PS-I ) into the cryogel matrix allows the photosensitized reduction of the Fe 3+ -CMCMA cryogel to the lower stiffness state Fe 2+ -CMCMA, and the concomitant, temporal, aerobic recovery of Fe 2+ -CMCMA to the high-stiffness Fe 3+ -CMCMA gel. The transient dissipative stiffness of the Fe 3+/2+ -CMCMA cryogel is characterized by temporal rheometry, dynamic stretching stress–strain experiments, XPS, and SEM imaging. The transient chemical/light-triggered stiffness functions of the Fe 3+/2+ -CMCMA, or PS-I-integrated Fe 3+/2+ -CMCMA gels are applied to develop transient self-healing matrices, and frameworks for cyclic, transient release of loads integrated in the gel matrices. This is exemplified by the ascorbate/light-induced cyclic transient release of tetramethyl rhodamine-dextran ( TMR-D ), insulin, and the anti-VEGF aptamer loads. In addition, the stimuli-responsive Fe 3+/2+ -CMCMA cryogel is used to construct a bilayer-soft-robotic bending device. Bilayer composite consisting of thermoresponsive poly- N -isopropylacrylamide ( pNIPAM )/Fe 3+/2+ -CMCMA, or pNIPAM/PS-I-loaded-Fe 3+/2+ -CMCMA devices are assembled. Switchable, reversible, and transient, thermal and chemical/light-triggered bending of the bilayer devices are demonstrated.