Abstract
This article presents two different microfluidic schemes that are capable of emulsification and multi-step chemistry synthesis. With different integrated functions, PDMS micro-device is able to produce double emulsification with controllable geometries and composition; moreover, multi-step synthesis of semi-permeable micro-encapsulation in a single chip. Three-layered PDMS molding and bonding process is used to fabricate the proposed microfluidic devices with pneumatically actuated diaphragm valves constructed on top of specially designed fluidic-channels are utilized to generate, meter, trap, filter the droplets and, consequently, the encapsulation process. A governing computer program cooperating with a set of control hardware was employed to coordinate the actuation of the prototype system. In the prototype demonstration, droplets was generated with desired size and frequency by alternating the open and close period of diaphragm valve. Emulsion droplets functioning as templates and reactors. During the synthesis process, relatively small Na-alginate droplets are metered, trapped, and then drawn into relatively large CaCl2 droplets, while they react and form solid Ca-alginate micro-capsules on the interfaces. In addition, entrapment and transfer of the resulting capsules can also be performed on the same microfluidic system to further process Ca-alginate into semi-permeable alginate-poly-L-lysine (PLL). It has been demonstrated that: (1) both water-in-oil-in-oil and water-in-oil-in-water double emulsions can be produced; (2) the sizes of inner aqueous droplets and outer oil drops can be controlled independently; (3) adjacent oil drops with varying overall sizes, and both diameters and numbers of inner aqueous droplets can be produced; (4) multi-step reactions could be performed on droplet-in-droplet interfaces to synthesize alginate-PLL capsules; and (5) on demand, controlled encapsulation could be achieved on an integrated microfluidic system. As such, the demonstrated emulsification and multi-step synthesis schemes could potentially fulfill the real-time controllability on emulsion formation and micro-encapsulation, which is desired for a variety of biological and medical applications.