Kinetics of coacervation transition versus nanoparticle formation in chitosan-sodium tripolyphosphate solutions

Colloids Surf B Biointerfaces 81(1):9 (2010) PMID 20674298

Chitosan (deacetylation=75-85%) and sodium tripolyphosphate (TPP) solutions were observed to undergo spontaneous coacervation transition or nanoparticle formation depending on the chitosan concentration and the volumetric mixing ratio [chitosan/TPP]. Three distinct conditions have been identified: (i) [chitosan]@?0.5mg/ml, 0.5@?[chitosan/TPP]@?2 and pH=2 and 3.5<7.5, favors induced coacervation. Sizing done by TEM and dynamic light scattering studies revealed that chitosan nanoparticles had typical diameter in the range ~150-350nm depending on polymer concentration and chitosan/TPP mixing ratio, which reduced by ~40% when polyethylene glycol (PEG) was added to these solutions. The long-time light scattering probing of the solutions revealed that residual interactions continuously produced soluble intermolecular complexes over extended period of time, a process that enabled the generation of coacervate droplets seamlessly. The coacervates (formed spontaneously or induced), and chitosan and chitosan-PEG nanoparticles, were used for encapsulating hydrophobic protein synthesis inhibitor model drug cycloheximide. The comparative in vitro release profiles in phosphate buffer and simulated intestinal fluid was monitored at 37^oC.