Controlled Sol–Gel\nTransitions of Metal–Organic\nMembrane-Enveloped Cellulose Nanofibrils via Metal Coordination in\nAqueous Media

We report a metal coordination-driven sol–gel\ntransition\nsystem where cellulose nanofibrils are enveloped by a rationally designed\nmetal–organic membrane (MOM) in an aqueous medium. Specifically,\n2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-oxidized bacterial cellulose\n(TOBC) is encapsulated within an MOM comprising Zn<sup>2+</sup> and\nthe chelator phytic acid (PA), denoted TOBC<sub>MOM</sub>. Using the\nDLVO theory, we elucidate how tuning the metal ion valence in TOBC<sub>MOM</sub> modulates the sol–gel transition by controlling\ninterfibrillar attractive forces. Notably, TOBC<sub>MOM</sub> fluids\nexhibit relaxation times consistent with the Kohlrausch–Williams–Watts\n(KWW) function. Significantly, we demonstrate reversible, sustainable\nsol–gel transitions in TOBC<sub>MOM</sub> under stepwise mechanical\nstrain. This facile approach enables rheological tailoring of aqueous\nmedia, promising for the development of advanced stimuli-responsive\nsmart fluids for applications in cosmetics, food science, and pharmaceutical\nformulations.