Confocal analysis of cellulose nanocrystal (CNC) based hydrogels and suspensions

Cellulose nanocrystal hydrogels, while mechanically weak, have high water content, are biocompatible and easily processed. Further improvement is needed to make cellulose nanocrystal hydrogels mechanically stable and self-healable. Herein, using quantitative fluorescence signal analysis, we assess stability, collapse, and level of self-healing of cellulose nanocrystal hydrogels with different cellulose nanocrystals and sodium chloride concentrations. We use the mean signal intensity obtained by confocal laser scanning microscopy to measure signal loss of the samples made of cellulose nanocrystal with different concentrations and as a function of initial gel height and sodium chloride loading. The cellulose nanocrystal dynamics inside the gels based on universality curve is unraveled which links the zeta potentials to the immobile particle percentages and the storage modulus as a function of sodium chloride/cellulose nanocrystal concentration ratio. Fluorescence recovery after photobleaching recovery analysis shows that for the ratio of sodium chloride/cellulose nanocrystals beyond 0.1, the mobility of the ensemble of cellulose nanocrystals particles becomes severely restricted. Hydrogel sample with low cellulose nanocrystal 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 concentration (30 g/L). Increasing the cellulose nanocrystal concentration hinders particle mobility and thus impedes the self-healing process. Quantification of the gel collapse behavior of cellulose nanocrystal gel and its self-healing property is critical in many applications, including water and air filters, oil spill sponges, and tissue engineering.