Microfluidic device utilizing pneumatic micro-vibrators to generate alginate microbeads for microencapsulation of cells

This study reports a new microfluidic device for continuous generation of alginate microbeads. The working mechanism is based on the use of a pneumatically driven micro-vibrator to continuously generate tiny alginate microdroplets into a thin oil layer. The temporarily formed alginate microdroplets soon sink into a sterile calcium chloride solution to form jelled microbeads. By regulating the flow rate of the alginate suspension and the pulsing frequency of the micro-vibrator, the size of the alginate microbeads can be controlled. Experimental results showed that alginate microbeads with sizes ranging from 73 to 302 μm in diameter can be generated at suspension flow rates and vibration frequency ranges of 1.48–9.35 μl/min and 2–16 Hz, respectively. For the aforementioned parameter ranges, the alginate microbeads had reasonable size uniformity with coefficients of variation from 3.8% to 7.8%. Moreover, its application for the microencapsulation of chondrocytes in alginate microbeads has also been demonstrated with high cell viability (94 ± 2%). As a whole, the proposed device has opened up a route to generate alginate microbeads or microencapsulation of cells in a simple, continuous, controllable, uniform, and cell-friendly manner with less contamination.