Evaluation of ultrasonic atomization as a new approach to prepare ionically cross-linked chitosan microparticles

Ultrasonic atomization was evaluated as a new approach for the preparation of ionically cross-linked controlled-release chitosan microparticles loaded with theophylline as the model drug, using tripolyphosphate (TPP) as counter-ion. It was possible to nebulize both 2% and 3% (w/v) chitosan solutions as a function of their viscosity, usually not processed by employing the conventional nebulizer. The results of the chitosan molecular characterization using the SEC-MALS analysis revealed that ultrasonic atomization caused a certain depolymerization, probably due to the main chain scission of the 1,4-glycosidic bond; however, Fourier transform-infrared spectroscopy revealed the absence of other chemical modifications. The ultrasonic atomization allowed preparation of TPP cross-linked chitosan microparticles mostly ranging between 50 and 200 mum. As regards manufacturing parameters, the linking time and washing medium were found to affect the properties of the microparticles, while the stirring rate of the TPP solution did not show any influence. The evaluation of the formulation variables revealed that chitosan concentration strongly affected both the feasibility of the ultrasonic atomization and the drug release. All the microparticles showed an encapsulation efficiency of > 50 % and, after an initial burst effect, a controlled release of drug for 48 h. In conclusion, the ultrasonic atomization could be proposed as a robust and innovative single-step procedure with scale-up potential to successfully prepare ionically cross-linked chitosan microparticles.