This paper describes the pure passive scheme that manipulates the multiple streams using microfluidic device. This device relies on capillarity to control merging of two streams and to regulate the volumetric flow rate (VFR). This sophisticated manipulation of the capillarity is, however, nontrivial due to the lack of the passive and precise means. Here, we control the capillarity precisely and rapidly through the geometry of the junction of two streams and the hydrophilicity of the substrate. Additionally, we use the relative flow resistance to control the VFR ratio of the merged two streams. This passive scheme leads to the significant simplification of the control of the multistream without sacrificing the rapidity and precision. When combined with the microfluidic components such as mixers, reaction chambers, and detectors, this passive scheme offer the possibility of designing disposable and integrated microfluidic systems.
We present a novel technology for a cyclo-olefin-copolymer (COC) plastic microfluidic platform for heat control with fully semiconductor process-compatible photolithographic 5 μm-wide metal patterns, for heaters, electrodes, and temperature sensors and a thin membrane structure. Through tests of compatibility of some thermoplastic materials with chemical solutions and temperature tolerance to the semiconductor processes (thin film depositions, photolithography, and etchings), we selected COC as a semiconductor process-compatible plastic material for biomedical applications. For photolithography processes, we manufactured the 5’ COC wafer with flat surface with c.a. 3 nm surface roughness, employing a novel flame-torched injection-molding method. Furthermore, the part of heating blocks on COC wafers is controlled thickness to the 100 μm, to enhance the heat-ramping speeds through reduction of the thermal mass. In order to fabricate the Au thin film micro-patterns for temperature sensors, heaters, and electrodes, Au film (100 nm) was deposited by e-beam evaporator and patterned by using standard photolithography, and wet-etched. The micro-patterned Au temperature sensors, heaters, and electrodes was demonstrated. For insulating layers, Al2O3 film was deposited by an ALD system, patterned by using the standard photolithography, and wet-etched. Using the COC microfluidic platform, we tested thermal cycling with simple heating and natural cooling on chip with water and, heating rates (5°C/s when heating, 3°C/s when cooling) are obtained. Therefore, the COC microfluidic platform can be applied to a DNA lab-on-a-chip.
A novel polymer microfluidic device for self-wash using only capillary force is presented. A liquid filled in a reaction chamber is replaced by another liquid with no external actuation. All the fluidic actuations in the device is pre-programmed about time and sequence, and accomplished by capillary force naturally. Careful design is necessary for exact actions. The fluidic conduits were designed by the newly derived theoretical equations about the capillary stop pressure and flow time. Simulations using CFD-ACE+ were conducted to check the validity of theory and the performance of the chip. These analytic results were consistent with experimental ones. The chip was made of polymers for the purpose of single use and low price. It was fabricated by sealing the hot-embossed PMMA substrate with a PET film. For simpler fabrication, the chip was of a single height. The embossing master was produced from a nickel-electroplating on a SU8-patterned Ni-plate followed by CMP. The contact angles of liquids on substrates were manipulated through the mixing of surfactants, and the temporal variations were monitored for a more exact design. The real actuation steps in experiment revealed the stable performance of selfwash, and coincided well with the designed ones. The presented microfluidic method can be applicable to other LOCs of special purposes through simple modification. For example, array or serial types would be possible for multiple selfwashes.