Chitosan (CS) is a natural biopolymer derived by deacetylation (N-acetyl-D-glucosamine to D-glucosamine unit) of chitin.
Chitosan (CS) is a natural biopolymer derived by deacetylation (N-acetyl-D-glucosamine to D-glucosamine unit) of chitin, which has been studied for its effectiveness against bacterial, fungal, and viral pathogens [9]; in addition, CS has demonstrated minimal toxicity in mammals and humans [10]. CS owns a molecular weight (MW) between 10 and 1000 kDa [11], but the MW and degree of acetylation (DA) depend on the type of source [12]. In principle, the DA is defined as the proportion of N-acetyl-D-glucosamine units with respect to the total number of units [11,13]. CS can be obtained from several sources including sea animals (e.g., annelida, mollusca, coelenterate, and crustaceans), insects (e.g., scorpions, spiders, ants, cockroaches, and beetles), microorganisms (e.g., algae, yeast, fungi, ascomycetes, and spores), among others [14]. The different MW and DA of chitosan also influence its physicochemical properties, such as solubility, appearance, rheological properties, among others [11], directly impacting the bioactivity and toxicity of the polysaccharide [10]. CS is a viscous polysaccharide that forms more structured gels when its MW increases; furthermore, it is considered as a pseudoplastic material since its viscosity is a function of concentration, temperature, and rate of shear [11]. The solubility of CS varies depending on DA, and it is insoluble in neutral-alkaline pH but highly soluble in acid pH due to the proportion of protonated amino groups (-NH2) that are positively charged [15]. Depending on its DA, the CS-polyelectrolyte takes different behaviors in solution; for example, if DA is greater than 50%, the molecule maintains the hydrophobic characteristics of chitin, while for a DA between 20% and 50%, the molecule becomes less hydrophobic, and CS, having a DA less than 20%, is considered a highly hydrophilic cationic polyelectrolyte [16]. CS can form amorphous and complex three-dimensional structures due to its polycationic nature that allows it to interact electrostatically (by hydroxyl groups), or to form covalent bonds by -NH2 groups, with other molecules, such as metals, surfactants, proteins, and polyanions [14].
This entry is adapted from the peer-reviewed paper 10.3390/polym13050767