Be careful and don't accidentally compare apples with oranges

Again, and again we come across publications in which chitosans are compared with each other. For example, we recently came across a paper comparing chitosan from crustaceans with that from fungi in bone tissue engineering applications (Iqbal et al. 2024). But to what extent was it actually valid?

Two chitosans were compared, which were described as high molecular weight by their respective manufacturers and therefore the author assumed that both chitosans were comparable. But is this true? Clues can be found by taking a closer look at the molecular weight, viscosity and degree of deacetylation (DDA). The specifications of both chitosans were as follows:

The molecular weight provides information about the chain length of the chitosan. Depending on the molecular weight of the chitosan, the viscosity of the chitosan in solution varies widely. While in this publication the mushroom chitosan with a molecular weight of 200-300 kDa had a viscosity of 600 mPas, the crustacean chitosan had a significantly higher viscosity of 2000 mPas with a molecular weight of 330-375 kDa. Since the Crustacean chitosan had a viscosity in solution more than twice as high as the fungal chitosan, the two chitosans are difficult to compare.

If you look at the DDA of both chitosans, the next hurdle in comparability arises. The DDA indicates the percentage of amine groups in the chitosan that are deacetylated, i.e. de facto how many positive charges are on the molecule. Looking at the two chitosans used, it is noticeable that the mushroom chitosan has a very high DDA of 98.1 %, while only a range is given for the crustacean chitosan. With ≥ 75 %, this could mean that it is either much lower than that of the fungal chitosan or very high and therefore comparable. However, this is not known until it has been determined. This again shows how important it is for manufacturers to provide detailed information about their chitosan.

According to Aranaz et al. (2009), the molecular weight, the DDA and both in combination significantly influence the biological properties of chitosans, such as biocompatibility, biodegradability, antibacterial effect or haemostatic properties. As a result, the chitosans considered in the publication are not only different in terms of their physiochemical properties, but may also have different biological properties.

Accordingly, it is impossible to determine the differences between the two chitosans in the publication in bone tissue engineering only on the basis of their source. The differences in molecular weight and the degree of deacetylation alone, regardless of whether they are fungal or crustacean chitosans, can already have a significant influence on their physiochemical and biological properties.

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Literature:

Iqbal, N.; Ganguly, P.; Yildizbakan, L.; Raif, E.M.; Jones, E.; Giannoudis, P.V.; Jha, A. Chitosan Scaffolds from Crustacean and Fungal Sources: A Comparative Study for Bone-Tissue-Engineering Applications. Bioengineering 2024, 11, 720. https://doi.org/10.3390/bioengineering11070720

Aranaz, Inmaculada & Mengíbar, Marian & Harris, Ruth & Panos, Ines & Miralles, Beatriz & Acosta, Nick & Galed, Gemma & Heras, Angeles. (2009). Functional Characterization of Chitin and Chitosan. Current Chemical Biology. 3. 203-230. 10.2174/187231309788166415.