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Open microfluidics is an emerging field of bio/medical applications that need direct energy/matter exchange between microfluids and environment. This paper presents the design, simulation, fabrication, and test of a microfluidic chip for a water-in-oil (WiO) two-phase flow in closed-open-closed microchannels. The chip, fabricated from PDMS using soft lithography, consists of a flow-focusing structure for WiO droplet generation and a long closed-open-closed channel for droplet flow. A negative pressure applied to the end of the channel is used as the driving force for WiO droplets to flow through the open channel. It is found that the negative pressure that is capable of driving a steady flow for a given flow rate, without overflow and air suction, falls into a pressure range instead of being an exact value. The mechanism for the pressure range is investigated theoretically and experimentally and is attributed to the surface tension. Yeast cells have been incorporated in the droplets, and the successful flow through the open channels verifies the function of the chips.

This paper reports the development of a hot embossing method for fabricating chalcogenide microlens arrays using soft polydimethylsiloxane (PDMS) stamps. The stamps are formed by molding PDMS on photoresist masters fabricated with sphere segments by thermal reflow. Upon proper temperatures, the chalcogenide glass softens and is embossed using PDMS stamps with low pressure. Void defects at the center and at the side of microlenses are found, and the mechanisms for the void formation are investigated and verified. The hot embossing parameters including pressure, temperature, embossing time, and the thicknesses of the PDMS stamps are optimized. A 400 × 400 microlens array with uniform profiles, smooth surface roughness, and good roundness have been successfully fabricated on both chalcogenide thin films and bulk wafers. The preliminary results demonstrate the feasibility of using hot embossing with soft PDMS stamps as a simple and low cost method to fabricate chalcogenide microlens arrays.