Direct super-resolution imaging of the disordered and crystalline nanostructure of bacterial cellulose fibrils

Cellulose is composed of tightly packed glucan chains that give it superior strength but render it recalcitrant to breakdown. The presence of dislocations susceptible to degradation within cellulose fibrils has been postulated for decades, but they have never been directly visualized. We have developed a super-resolution fluorescence microscopy approach to visualize alternating crystalline and disordered regions within bacterial cellulose fibrils. The measured size of crystalline regions ranges from 40 – 400 nm and matches the length distribution of cellulose nanocrystals produced through acid hydrolysis, while disordered regions are 20 – 120 nm long, heterogeneous and do not form large amorphous pockets. These results lend strong support for the fringed-micellar model of cellulose fibrils and provide fundamental insight into the role of cellulose nanostructure in its breakdown by chemical and enzymatic means.