Scalable production of chitosan sub-micron particles by membrane ionotropic gelation process

Ionotropic gelation (IG) is a highly attractive method for the synthesis of natural water-soluble polymeric nanoparticles (NPs) and sub-micron particles (sMP) due to its relatively simple procedure and the absence of organic solvents. The method involves the electrostatic interaction between two ionic species of opposite charge. Although it is well studied at the laboratory scale, the difficulty to achieve size control in conventional bench-top process is actually a critical aspect of the technology. The aim of this work is to study the membrane dispersion technology in combination with IG as a suitable scalable method for the production of chitosan sub-micron particles (CS-sMPs). The two phases, one containing chitosan (CS) and the other containing sodium tripolyphosphate (TPP), were put in contact using a tubular hydrophobic glass membrane with a pore diameter of 1 μm. TPP (dispersed phase) was permeated through the membrane pores into the lumen side along which the CS solution (the continuous phase) flowed in batch recirculation or continuous single-pass operation mode. The influence of chemical variables (i.e. pH, concentration and mass ratio of polyelectrolyte species, emulsifier) and fluid-dynamic parameters (i.e. polyelectrolyte solution flow rate and their relative mass ratio) was studied to precisely tune the size of CS-Ps.