Characterization of spray dried chitosan–TPP microparticles formed by two- and three-fluid nozzles

Chitosan microparticles cross-linked by tri-polyphosphate (TPP) anions have been prepared by spray drying. Two different cross-linking methods have been employed — ex-situ cross-linking whereby aqueous solution of cross-linked chitosan nanoparticles has been spray-dried by a two-fluid nozzle, and a novel in-situ cross-linking method, whereby solutions of chitosan and TPP have been fed to a three-fluid nozzle and cross-linking occurred within individual droplets. The size and morphology of the resulting microparticles have been characterised and their dependence on the cross-linking ratio and the initial chitosan concentration determined. Particles produced by the three-fluid nozzle were found to have favourable properties in terms of stability in aqueous media and they allow the use of higher chitosan concentrations, which makes them suitable for microencapsulation applications.

Graphical abstractChitosan microparticles cross-linked by tri-polyphosphate (TPP) anions have been prepared by spray drying using ex-situ and in-situ cross-linking methods. The novel in-situ cross-linking method is based on a three-fluid nozzle where cross-linking occurs within individual droplets. The size, morphology and swelling of the microparticles as function of composition and cross-linking method were systematically investigated.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Cross-linked chitosan particles produced by spray drying. ► Effect of composition on size and swelling investigated. ► Two- and three-fluid nozzles compared. ► Internal core–shell structure confirmed by confocal microscopy.