C. C. Lai

Numerical analysis and experiments of capillarity-driven microfluid chip

Pumping of fluid is an important issue in the microfluidic system. Surface-directed capillary pump merits no external power input and low pressure drop in the microchannel compared to external syringe pump and built-in powered pumps. In this article, the numerical analysis and experiments of the capillarity-driven fluidic flow in the microchannel have been investigated. Varied width-to-depth-ratio microchannels were designed for simulation and experiments. The surface hydrophilicity of PDMS and glass materials was examined for fluidic chip fabrication and flow test. Low-viscosity DI water and high-viscosity human blood were used for capillarity-driven flow measurement. PDMS surface was first performed by oxygen plasma treatment for hydrophilic surface to enhance capillary force. But the hydrophobic recovery of PDMS occurred several ten minutes after oxygen plasma treatment. So, the intrinsic hydrophilic glass chips were used for high-viscosity human blood test. The flow velocity of fluid was relevant to the channel geometry and fluidic viscosity. It increased with width-to-depth ratio at constant channel depth and decreased with viscosity. The experimental results had a good agreement with simulation. It offered a good reference for future capillarity-driven microfluidic device in biomedical or biochemical application.

Fabrication of microfluidic chip using foil-assisted CO2 laser ablation for suspended particles separation

Lab on a chip was mainly used in the simplification of biomedical detection step and separation was one of the indispensable pretreatment during the detection process. In this study, a combination channel of spiral and backward facing step patterns were designed to optimize the separation function without any extra power like electric or magnetic field. The foil-assisted CO2 laser method was used to fabricate a spiral microfluidic chip with polymethylmethacrylate polymer for the master of suspended particles separation. The laser ablation generated poor surfaces quality with bulge and scorches can be diminished using foil-assisted laser micromachining technique. The low-cost and time-saving procedure, including microchip fabrication and surface modification, has been developed to apply positively in microfluidic separation chip based on the flow distribution design of spiral dean vortices and backward facing step, which can provide 99% separation efficiency within a certain flow range.

Simulation and experiment of capillary driven passive planar baffle micro-mixer

In this study, we present a capillary driven and easily fabricated passive planar baffle micro-mixer with a trigger valve. The micro-mixers were fabricated in PMMA sheets (2 mm in thickness) by CO2 laser ablation and thermal bonding, and the microfluidic experiments were observed and recorded using flow visualization with a CCD. The results show that design of channel height ranges (to 220~400 μm) can be promoted by modifying the staggered baffle structure, and the meander baffle structure mixer performs the best mixing efficiency (94%) because of longest flow time and shortest average diffusion distance (300 μm) in mixing zone.