What are chitosan nano-particles, nano-capsules, and nano-fibers?

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When chitosan solutions are mixed with polyanionic compounds (i.e. molecules with multiple negative charges) under vigorous stirring, they can easily form nano-sized particles. These chitosan nano-particles typically have diameters in a wide range of 150 to 1000 nm and are thus, by definition, not true nano-particles (the size of which is below 100 nm). Chitosan polymers can also form an outer layer surrounding nano-sized oil droplets in an aqueous emulsion, thus forming nano-capsules, and chitosan polymers can also be spun into nano-sized fibers. All of these nano-materials of chitosans can be loaded with different types of molecules, such as medicinal drugs, genes, or vaccines. Due to their polycationic nature (having multiple positive charges), nano-formulated chitosans easily bind to the polyanionic surfaces of cells (having multiple negative charges) and are then often taken up into the cells, delivering their cargo to the cells. This makes chitosan nano-formulations very interesting for biomedical and pharmaceutical applications, but it also asks for rigorous toxicity studies before chitosan nano-formulations can be approved for such uses.