High throughput fabrication of microdroplets using needle based microfluidic system

Needle-based microfluidic system that comprised of needle-based microfluidic devices (NBMD) in parallel connection was employed to generate polydimethylsiloxane (PDMS) microdroplets using oil-in-water (O/W) single emulsion template. The parallel-connection could be simply realized by multiple single NBMD connected via flow diverting devices. The versatile flow diverting devices could not only avoid the additional use of injection pumps for introducing fluids into the microfluidic system, but also enhance the yields of microdroplets. The entire production rate of the system has been raised to 535 drops per minute compared with that using a single NBMD which yields to 133 drops per minute. All the microdroplets were produced under dripping flow regime. If identical flow conditions and channel diameters were applied, the generated microdroplets from the each microchannel could have high monodispersity. Despite of several parameters that could affect the droplet sizes, for example, flow rate exerted on each channel and the channel size which depended on the selection of various needle combinations of the inlet and outlet needles, the inter-needle distance between those two needles may significantly influence the size of droplets. Thus, it shall be controlled carefully to remain the same distance in terms of achieving high monodispersity of the droplet sizes. On the other hand, one can vary the sizes of needles applied in the same batch of production or by adjusting the inter-needle distance in order to realize the production of microdroplets with various sizes. Moreover, diverse types of microdroplets could be produced simultaneously through different channels by NBMD. In this research, sugar and multi-walled carbon nanotubes (CNTs) were utilized as dopants mixing with PDMS precursor as the dispersed phase to produce PDMS-S and PDMS-CNTs microdroplets. The droplets could be collected and thermally solidified off-site for other applications. This platform does not require sophisticated equipment and is very cost-effective compared with conventional microfluidic devices such as PDMS devices or glass capillary devices. Hence, the system has great potential to produce microdroplets at a large scale.