Flexibility of backbone fibrils in α-chitin crystals with different degree of acetylation

Acetyl groups are backbone outreaches that enhance inter-fibril connection in chitin and chitosan fibril bundles. Removal of acetyl groups affects flexibility of chitosan fibril bundles, thereby affecting mechanical strength of chitosan-based products. Understandings of relationship between degree of acetylation and flexibility of chitin fibril bundle conduce to optimization of synthetic chitin materials. Here, the relationship is examined by performing molecular dynamics simulations. Coiling of chitin and chitosan fibril bundles with different degree of acetylation is observed. Flexibility of fibrils is measured. Number and alignment of acetyl groups are found to be important factors determining flexibility of chitin and chitosan fibril bundles. Structural instability can be caused by incompatible alignment of acetyl groups. Discussions on synthetic chitin-based materials imply that adding a small amount of acetyl groups to chitosan can significantly enhance fibril bundle integrity.