RESEARCHMicrofluidics, as a scientific field dealing with nano to pico-liter scale fluid, has made remarkable advances in the past decade. Microfluidic techniques provide important research tools for many fields and it is especially favorable for biosensor applications due to its capability to control micro environments. In addition, microfluidics as an independent subject is also very interesting, involving various areas from theoretical fluid dynamics to engineering of microfluidic components. It is expected that microfluidics will expand its area further by exploring new frontiers, which will require multidisciplinary collaborations from variety of backgrounds.
Inertia in a microfluidic system can allow manipulations of micro particles and fluid flows. In these finite Re flows, microparticles or cells migrate across streamlines due to hydrodynamic forces (shear gradient lift force, wall-induced lift force and Dean drag force) in a predictable manner and line-up along distinct equilibrium positions. Focusing positions are controllable with various parameters such as channel geometry, Re and fluid properties. These microfluidic systems can be developed as passive and high-throughput particle or cell sorters. Inertial focusing can be further used for biological applications such as flow cytometry or lab-on-a-chip systems for rare cell separations. We are investigating inertial focusing according to different channel cross-sectional shapes and effects of varying viscosity with co-flow system.
Using micro-patterning techniques and MEMS fabrication methods, we develop microchip-calorimeters with a ultra-high resolution. Thin-film parylene microfluidics are used for chip calorimeters to create a stable thermal insulation. Microchip-calorimetry can measure and record continuous output of heat from a small heat source. Microchip-calorimeters can be applied to wide range of application in chemistry, life sciences, and medicine according to various types of measured heat sources. We apply chip calorimeter to measure accurate doses of radiation for radiotherapy or to measure metabolic rates of cells.
Flexible microfluidics and sensors
Parylene-based, thin-film microfluidic system is developed to achieve flexible microfluidics with microscale bending radius. The flexible parylene channels can be integrated with flexible electronics for manipulation and analysis of body fluids. Flexible microfluidics can also be applied to a rollable microfluidics system. In rollable microfluidics, 2D parylene channels can be rolled around capillary tubings working as inlets to minimize device footprints. In addition, reconfigurable 3D channel geometry with microscale bending radius can lead to tunable device function.
Unconventional microfabrication techniques
In our laboratory, novel unconventional fabrication process is studied for the potential of rapid, quantitative, and sensitive analysis.
Micro-prism mirror embedded 3D chip
We developed the prism-mirror-embedded microfluidics device that allows simultaneous imaging of top and side view of a microchannel with one microscope without extra expensive optical equipments. The mirror-embedded 3D imaging microchannel is made by conventional microfabrication techniques including wet etch and soft lithography and capillary molding. Using the microchannel, 3D information of particle positions and complex flow patterns with microfluidics channel can be acquired in real time.
Tunable parylene microfluidic lens
Parylene microfluidic lens can provide tunable focal length by changing the radius of curvature of the lens or the refractive index of filling liquid. Parylene has low gas permeability and is chemically inert which allows it to encompass diverse filling liquids. Due to parylene’s excellent properties, microlens showed same deflection for the applied pressure in 500 repeating cycles in elastic region.
Microfluidics platform for individual cells analysis
We develop microfluidics platform for single cell analysis by assembling PDMS and PEG coated cover-slides reversibly with negative pressure. Cells can be captured individually and cell signaling analysis can be performed at fixed positions with bait protein. This approach provides cell-to-cell signaling pathway variation compared to previously averaged out signals in single-molecule Co-IP.
Nanofluidic TEM chip
Nanofluidic, liquid cell TEM chip technologies have been under the spotlight in biochemistry and material sciences because it can reveal the mechanism of material process or biological samples in hydrated states. Furthermore, our works are not only focused on static liquid cell TEM but also on dynamics study in nanofluidic chips. We are interested in all fabrication techniques for nanofluidic TEM chip including MEMS, direct bonding and highly electron transparent window materials such as graphene.