Effect of Process Parameters on Microencapsulation of Active Compounds by Co-flow Air Assisted Microfluidic Extrusion

Abstract

A co-flow microfluidic system consists of two concentric channels inside which flow the inner dispersed phase (sodium alginate) and the outer continuous phase. The size and shape of microbeads depend on the physical-chemical properties and flow rate of fluids and on the process conditions such as diameter, material type of dripping tip and collecting distance. In order to reduce the microbeads size, external forces are used to break up the droplets. These forces could be generated by pressurized air, electrostatic charges and vibration. The technologies presented in literature for matrix encapsulation are based on a liquid-liquid dual immiscible fluid configuration, introducing a series of problems in industrial production, like gelation, oil separation and cleaning which would not arise using air as continuous phase. However, the use of air introduces a more complex fluid dynamics in possibly turbulent flow regime. The aims of this study include: firstly the developing an integrated system pump-microfluidic device; secondly the analysis of the size of Ca-alginate beads at different air flow rates setting the dispersed phase flow rate at 1 ml min-1; and finally the study of the influence of alginate sodium flow rate on beads size distribution and the capsules payload . For these purposes, a 3% (w/v) solution of sodium alginate was used. The air focused the dispersed phase at dripping tip, applying a shear force generating micro-droplets. A 0.2 M solution of calcium chloride dehydrate allowed the extruded drops gelation. Then, the size distribution was investigated using laser diffraction. The results showed that the size of microbeads decreased with increasing air flow rate (from 0.7 to 2.4 ln min-1).