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

The synthesis of redox-active Fe³⁺-cross-linked carboxymethyl cellulose methacrylate cryogels (Fe³⁺-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 Fe²⁺-CMCMA gel, and the concomitant aerobic oxidation of the Fe²⁺-CMCMA to the Fe³⁺-CMCMA gel state. Alternatively, integration of native photosynthetic photosystem-I (PS-I) into the cryogel matrix allows the photosensitized reduction of the Fe³⁺-CMCMA cryogel to the lower stiffness state Fe²⁺-CMCMA, and the concomitant, temporal, aerobic recovery of Fe²⁺-CMCMA to the high-stiffness Fe³⁺-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.