Using a microfluidic chip and internal gelation reaction for monodisperse calcium alginate microparticles generation

In this paper, the manipulation of monodisperse Ca-alginate microparticles using a microfluidic chip and a reaction of internal gelation is presented. Our strategy is based on the sheath focusing effect to form uniform water-in-oil (w/o) emulsions in the cross-junction microchannel. These fine emulsions, consisting of 1.5 % w/v Na-alginate and 1.0 % w/v calcium carbonate, are then dripped into an oil solution containing 20 % v/v glacial acetic acid and 1 % v/v Tween 80 to obtain Ca-alginate microspheres in an efficient manner. The mechanism is that acetic acid reacts with the calcium carbonate to release the calcium ions, and these calcium ions, through crosslinking reaction with the alginate, produce Ca-alginate microspheres. We have demonstrated that it is possible to control the size of Ca-alginatemicroparticles from 80 microm to 800 microm in diameter (with a variation of less than 10 %) by altering the relative sheath/sample flow rate ratio. Experimental data has shown that for a given 0.01 mL/min of the dispersed phase flow (sample flow), the emulsion size decreased as the average velocity of the continuous phase (oil flow) increased. The same tendency was observed in the 0.05 mL/min and 0.10 mL/min of dispersed phase flow. The microfluidic chip is capable of generating relatively uniform micro-droplets and has the advantages of active control of droplet diameter, simple and low cost process, and a high throughput.