Stimuli-responsive composite hydrogels with three-dimensional stability prepared using oxidized cellulose nanofibers and chitosan.

Stimuli-responsive hydrogels have garnered the attention of the hydrogel industry, as they are able to change their physical and chemical properties based on changing external stimuli such as pH, temperature, ionic strength, electromagnetic fields, and light. However, stimuli-responsive hydrogel applications are hindered due to their inevitable swelling and shrinkage. Bacterial cellulose (BC), a natural hydrogel with tightly packed cellulose nanofibers (CNFs) was oxidized into dialdehyde BC (DABC) and was composited with chitosan (CS), a readily available natural polymer, to develop a mechanically adaptive hydrogel composite under different pH conditions. Composites exhibit pH sensitivity by presenting higher mechanical properties under acidic conditions and lower mechanical properties under basic conditions owing to the protonation of amino groups of the chitosan chains. Osmotic pressure is built up under acidic conditions, increasing the mechanical strength of the composites. The good three-dimensional stability of composites enables them to consistently maintain their volume when exposed to acidic or basic conditions.