What are First, Second, and Third Generation Chitosans?

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First generation chitosan is the poorly defined chitosan of the past, with large batch-to-batch differences and poor reproducibility in terms of structure and functions as well as purity. Second generation chitosans are today's best chitosans, well-defined in terms of their degrees of polymerization and acetylation, with narrow polydispersity and high purity. Third generation chitosans are tomorrow's chitosans which are expected to be even better defined, to have different, defined patterns of acetylation and well-known functionalities based on known modes of action. Many of the chitosans commercially available today are still first generation chitosan, but some producers can already provide industry scale amounts of second generation chitosans. Third generation chitosans are only available at lab scale, and mostly not commercially. The relatively poor quality of first generation chitosan led to a poor reputation of chitosan-based products, e.g. in cosmetic applications where it was first used. But research of the past twenty years has improved the understanding of structure-function relationships of chitosans, revealing that chitosans of different structures also have different functionalities. Concomitantly, analytical methods for chitosans were refined and these allowed to improve production processes, leading to today's reliable second generation chitosans.