Double dynamic cellulose nanocomposite hydrogels with environmentally adaptive self-healing and pH-tuning properties

Dynamic hydrogels are prepared by either dynamic covalent bonds or supramolecular chemistry. Herein, we develop a dynamic hydrogel by combining both dynamic covalent bonds and supramolecular chemistry that exhibits environmentally adaptive self-healing and pH-tuning properties. To do so, we prepared a gelatin–nanopolysaccharide mixed hydrogel containing pyrogallol/catechol groups and trivalent metal ions. The as-prepared hydrogels are able to heal damage inflicted on them under acidic (pH 3 and 6), neutral (pH 7), and basic (pH 9) environments. The mechanism of healing at acidic and neutral pHs is dominated by coordination bonds between pyrogallol/catechol groups of tannic acid and ferric ions, whilst Schiff-base reaction between amines from gelatin and dialdehyde-modified cellulose nanocrystals dominates the formation of dynamic hydrogels at basic pH. Self-healing mechanism of the hydrogel at all pHs occurred at ambient temperature without any external stimuli. The hydrogels also showed different mechanical, electrical, self-healing, and self-adhesiveness properties in different pH levels. Furthermore, the hydrogels showed printability and injectability at pH 6.