Rapid fabrication of circular channel microfluidic flow-focusing devices for hydrogel droplet generation

A rapid method to fabricate a flow-focusing microfluidic device with circular channels for droplet generation is presented. To create the desired 'polydimethylsiloxane (PDMS)' channel geometry, moulds using a rapid and cheap three dimensional (3D) printing process comparing with conventional microfabrication method have been fabricated. The 3D printer with a 16 mu m layer resolution utilised to fabricate 100 mu m half circular microfluidic moulds. The finished moulds were baked and silanized prior to casting to avoid the incomplete curing problem of the 'PDMS' castings. Casted 'PDMS' halves were aligned and bonded together to build complete microfluidic chips by an oxygen plasma treatment. Due to the resolution limitation of 3D printing, the channels were not perfectly circular rather than elliptical. A liquid 'PDMS' injection process was used and optimised to create fully circular channels, and also address challenges regarding the misalignment of the upper and lower halves of the microfluidic chip. Circular channels were successfully formed in the flow-focusing microfluidic device through the post ` PDMS' injection process without any blockage of the cross junction. The device functioned well to create similar to 200 mu m droplets.