Transport of cells

Figure 3 (A) Robot system for lipofection screening (A) Worktable with racks for microplates, buffer reservoirs, plastic, and glass vials. (B) Four tip liquid handling arm. (C) Gripper for transport of microplates and glass test tubes. (D) High power water bath sonicator. ( ) Nitrogen evaporator. (F) Microplate washer. (G) Absorbance reader. (H) Luminescence reader. (/) Transparent hood. (/) CO2 incubator with pneumatic door (from the rear, front view in B). (B) Self-constructed robotic conveyor for the transport of cell culture plates from the incubator to the worktable.

A single neuron-like PC 12 cell was trapped in an etched glass (30 pm deep) pocket sealed against a PDMS channel layer (20 pm). Quantal release of dopamine (in transient exocytosis) from the cell as stimulated by nicotine was amper-ometrically detected with a carbon fiber electrode. The cells flow into the channels caused by the liquid pressure which was provided by a liquid height at the sample reservoir (e.g., 0.5-2 mm). To facilitate transport of cells in the microchannels, the cell density should not be higher than lOVmL. Serious cell adhesion occurred if the transport speed was low (as provided by liquid height below 0.5 mm),... 

Another electrokinetic effect is based on polarization of particles within an oscillating electrical field or field gradient (dielectrophoresis), as depicted in Fig. 13c. Dielectrophoresis is applied in many fields, e.g. for the controlled separation and trapping of submicron bioparticles [245], for the fusion and transport of cells [246], or the separation of metallic from semiconducting carbon nanotubes [13, 247-249]. Other applications are cell sorting [250, 251] and apoptosis of cells [252, 253]. 

The work to be discussed here deals with platelet adhesion to protein coated surfaces. The protein coating, the cells on the surface and the moving fluid adjacent to the surface may be viewed as a system of interacting components. Flow is an important feature of this system since it brings new protein and cells to the system, augments the transport of cells to the surface and can cause the detachment of adherent cells. Each component of the system may influence the conditions of the other components. The variation of the surface concentrations of proteins on a solid substrate continues to be studied and remains a key area of interest. However, the action of immobilized cells on the substrate needs to be examined more carefully as well as their contribution of secreted substances to the fluid phase adjacent to the substrate and to the substrate protein itself Red cells, platelets and white cells may also adhere and detach from the substrate changing its make-up by yet another mechanism. 

The following conclusions can be drawn based on the work carried out to date. The multistage electrophoretic extraction concept was shown to be capable of electrokinetic transport of cells and particles. Although the depth of the chambers hampers the resolution of cell extraction, studies to date have paved way for new generation equipment. Resolution can be increased by decreasing the depth of the chamber and increasing the diameter or cross sectional area of the chambers. 

Microflow is realized as either electroos-motic flow (EOF) or pressure-driven flow. EOF is in many cases not suitable for transport of cell media due to its high ionic strength additionally, the electrical fields may cause adverse effects on a cell population. Thus, pressure-driven flow generated by off-chip or on-chip pumps is preferable for cell assays. On-chip pumps are particularly convenient - of note, pumps formed by multilayer soft lithography have been applied to analyzing T-cell behavior in microfluidic devices [6]. 

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