Chitosan is soluble in acidic conditions - in solution the free amino groups on its polymeric chains can protonate, giving it a positive charge. Chitosan nanoparticles can be formed by incorporating a polyanion such as tripolyphosphate (TPP) into a chitosan solution under constant stirring.
These nanoparticles can then be used for drug delivery and gene therapy applications. Due to its poor solubility at pH more than 6.5, a number of chemically modified chitosan derivatives with improved water solubility can be used as well.