In this study, the formation of sub-micrometric chitosan (CS) particles via supercritical assisted atomization (SAA) was investigated using supercritical CO2 spraying medium and aqueous ethanol solution (50%, v/v) as solvent. Results indicated that smaller CS particle were obtained by using low concentrations of the CS solution, high saturator temperatures, and an optimized CO2-to-CS solution flow ratio. Using the mixed-suspension, mixed-product-removal (MSMPR) population balance model, the precipitation kinetics parameters were determined from CS particle size distributions and the mass-weighted mean sizes of CS particles, which are a function of the precipitation parameters. An efficient tight junction opening effect was induced by the interaction of CS microparticles and Caco-2 cell monolayers as indicated by the marked decrease in the transepithelial electrical resistance (TEER) of Caco-2 cell monolayers incubated with CS particle suspensions. In addition, the reversibility of the TEER changed depending on the viability of the Caco-2 cells, and cell viability was high at low concentrations of CS suspensions. (C) 2015 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.