Cellulose nano crystal (CNC) hydrogels, while mechanically weak, have unique properties such as easy synthesis, high water content, and biocompatibility. Further improvement is needed to make CNC hydrogels mechanically stable and self-healable. Herein, using quantitative fluorescence recovery after photobleaching (FRAP) analysis, we assess stability, collapse, and level of self-healing of CNC hydrogels with different CNC and sodium chloride (NaCl) concentrations. We use the mean signal intensity obtained by confocal laser scanning microscopy (CLSM) to measure signal loss of the samples made of CNC hydrogels of different CNC concentrations and as a function of initial gel height and NaCl loading. The CNC dynamics inside the gels based on universality curves is unraveled which links the zeta potentials to the immobile particle percentages and the storage moduli as a function of NaCl/CNC concentration ratio. FRAP recovery analysis shows that for the ratio of NaCl/CNC beyond 0.1, the mobility of the ensemble of CNC particles becomes severely restricted. Hydrogel samples with low CNC concentrations (6 g/L and 10 g/L) experience a more substantial collapse rate under gravity than the rate observed for samples with a high CNC concentration (30 g/L). Increasing the CNC concentration hinders particle mobility and thus impedes the self-healing process. Quantification of the gel collapse behavior of CNC gel and its self-healing property is critical in many applications, including water and air filters, oil spill sponges, and tissue engineering.
