Controllable formation of microparticles via microfluidic technique

Abstract

Droplet microfluidics is an interesting tool in the encapsulation process due to its potentiality for microparticles and microcapsules fabrication with uniform size and narrow size distribution. The formation of water-in-oil (W/O) emulsion droplets in a microfluidic flow-focusing device for microparticles production were investigated under a wide selection of operating parameters together with liquid materials. Experimental results of 12 data sets from over 100 experiments in two different-sized channels were assessed. The stable narrowing jet and tip streaming regime noticeably created monodisperse droplet formation with high throughput. The droplet size to junction size has been found to correlate with the three dimensionless numbers which are flow rate ratio (Qc/Qd), viscosity ratio (µc/µd), and capillary number (Ca). This correlation will be beneficial in predictable and controllable monodisperse droplets in a high flow process regime. To generate either the microparticles or microcapsules using alginate as a carrier in a biphase system, it is necessary to focus on the crosslinking method. The internal gelation of alginate microparticles using a water-soluble calcium-ethylenediaminetetraacetic acid (Ca-EDTA) as a calcium source was studied to control crosslink density and the shape of particles. Effects of emulsification speed, Ca-EDTA concentration, crosslinking time on morphology, %yield, mechanical properties, rheological properties, and Ca content for crosslink density were studied in the oil (W/O) emulsification method. The optimum condition of internal gelation was used in the microfluidic technique which generated monodisperse alginate particles with more uniformity and controllable size. Then, singled- and multipled-core-shell microcapsules were fabricated by connecting two flow-focusing microfluidic chips. The oil droplets as a core were first formed and then entrap with the alginate substance via microfluidic technique and crosslinked to a solid shell. Droplet size and shell thickness over the operating parameters were studied. The resultant would show a great potential application in the field of food and pharmaceutical encapsulation.