Preparation of chitosan-TPP sub-micron particles: Critical evaluation and derived recommendations

• The sensitivity of properties of chitosan-TPP particles to experimental conditions.
• The conformation of chitosan influences the stoichiometry of crosslinking.
• Dialysis of chitosan-TPP particles after preparation improves colloidal stability.
• High-frequency data acquision in DLS analysis is strongly recommended.

The controlled preparation of chitosan particles is far from being trivial due to a considerable number of experimental parameters. For chitosan-tripolyphosphate (TPP) particles we evaluate the impact of chemical (type of chitosan, concentration, chitosan to TPP ratio, pH, ionic strength) and process factors (dialysis, stirring rate, rate of TPP addition, temperature, needle diameter) on the size and colloidal stability. The particles were prepared at pH = 6.0 at which chitosan adopts the coiled conformation that is discussed as the dominant factor in controlling the stoichiometry of crosslinking reaction shifted towards TPP. These conditions result in identical particle size around 400 nm and zeta potential around 22 mV. The colloidal stability evaluated 24 hours after preparation depends on the amount of TPP during crosslinking. Under the same conditions, the colloidal stability up to 1 month is demonstrated. Several recommendations are provided to increase the control over formation of chitosan-TPP particles.