Manufacture of chitosan microbeads using centrifugally driven flow of gel-forming solutions through a polymeric micronozzle

A centrifugally driven pulse-free flow has been used for generation of tripolyphosphate (TPP)-gelated chitosan beads with tunable diameters ranging from 148 to 257 lm. The production process requires a single motor as the sole actively actuated component. The 2% (w/w) chitosan solution was extruded through a polymeric nozzle with an inner diameter of 127 lm in the centrifugal field ranging from 93 to 452g and the drops were collected in an Eppendorf tube containing 10% (w/w) TPP solution at pH 4.0. The reproducibility of the bead diameters out of different nozzles was very good with overall CVs of the bead diameters down to 15% and the production rate was 45 beads per second per nozzle at 44 Hz rotor frequency. The production rate was proportional to the sixth power of the rotor frequency, which was explained by the non-Newtonian behaviour of the chitosan solution with a flow behaviour index of 0.466. An analytical model for the bead diameter and production rate has been presented and validated by the experimental data. The shrinkage of chitosan drops during gelation was estimated from the observations and the theoretical model.