Zhongliang Tang

Efficient capture of circulating tumor cells with a novel immunocytochemical microfluidic device

Ability to perform cytogenetic interrogations on circulating tumor cells (CTCs) from the blood of cancer patients is vital for progressing toward targeted, individualized treatments. CTCs are rare compared to normal (bystander) blood cells, found in ratios as low as 1:10(9). The most successful isolation techniques have been immunocytochemical technologies that label CTCs for separation based on unique surface antigens that distinguish them from normal bystander cells. The method discussed here utilizes biotin-tagged antibodies that bind selectively to CTCs. The antibodies are introduced into a suspension of blood cells intending that only CTCs will display surface biotin molecules. Next, the cell suspension is passed through a microfluidic channel that contains about 9000 transverse, streptavidin coated posts. A CTC making contact with a post has the opportunity to engage in a biotin-streptavidin reaction that immobilizes the cell. Bystander blood cells remain in suspension and pass through the channel. The goal of the present study is to establish the technical performance of these channels as a function of antigen density and operating conditions, especially flow rate. At 18 μL/min, over 70% of cells are captured at antigen densities greater than 30 000 sites/cell while 50% of cells are captured at antigen densities greater than 10 000. It is found that lower flow rates lead to decreasing cell capture probabilities, indicating that some streamlines develop which are never close enough to a post to allow cell-post contact. Future modeling and streamline studies using computational fluid dynamics software could aid in optimization of channel performance for capture of rare cells.

Electrokinetic flow control for composition modulation in a microchannel

A numerical and experimental study of the injection into a microchannel of a fluid with a spatially modulated composition is presented. The investigation employs test structures constructed in polydimethylsiloxane by standard replica molding. Fluid-flow simulations are compared to flow results obtained by fluorescence microscopy experiments. Results show that for a given channel dimension, the desired modulation of the solution composition is only possible below a threshold frequency. The value of the threshold frequency is dependent on channel size as well as flow rate. Experimental results are in accord with numerical simulations and theoretical considerations.

Simulation and experimental validation of electroosmotic flow in a microfluidic channel

Steady electroosmotic and pressure driven flows in geometries of interest to biomacromolecular detection are considered. For both types of flow, experimental data are obtained by imaging fluorescent dye propagation. Numerical simulations are carried out using finite volume methods. Test structures are made of polydimethylsiloxane (PDMS) mold using the negative of the desired structure fabricated by SU-8 thick negative photoresist. Steady electroosmotic flow is governed by the Laplace equation under certain idealized conditions such as when the Helmholtz-Smoluchowski relation is satisfied at the inlet and outlet boundaries, and when the zeta potential is uniform across the domain. Electroosmotic fluid flow can be further idealized as two-dimensional when two parallel plates confine the flow. Such conditions are frequently encountered in many microfluidic devices. Numerical solutions of such an idealized two-dimensional electroosmotic flow are obtained. Equations describing the transient dye propagation are then solved in a straight channel followed by a downstream circular well. Effects of channel size, electric field and possible pressure driven flow components are explored.

Novel Application of Microfluidic Channels in Studying Cell Migration and Reorientation in Response to Direct Current Electric Fields

Electric fields have been shown to induce cell migration (galvanotaxis) and cell shape changes (galvanotropism) in many cell types, such as neural crest cells, embryonic cells, and chondrocytes [1–3]. In this study, a novel microfluidic system was developed to study individual cellular responses to applied electric fields. These microfabricated channels are made from commercially available poly-dimethyl-siloxane (PDMS). This gas permeable, tough, and transparent polymer provides a sterile tissue culture environment and permits visualization of cells using epifluorescence microscopy. In conjunction with the device, a custom computer program was written to quantify the migratory behavior of cells by analyzing changes in position and cell shape. The flexibility of the channel geometry allows for a wider range of chamber resistance and applied currents (achieving a particular field strength) that may permit further study into the underlying mechanisms of electric field directed cell migration and orientation.© 2002 ASME