A Solution Exchange Platform for Exposure of Cells to Chemical Waves

Doctoral thesis, 2007

This thesis presents the development, characterization and suggested applications of a platform for controlling the chemical environment around a cell or a cell constituent. The platform is unique in its capability to combine rapid solution switching with precise timing and access to a manifold of solution environments. It can be used to present a sequence of different solution environments to a cell or cell constituent, with rapid switching between them. Furthermore, the system can be used to expose cells and their constituents to complex chemical waves and oscillations, either mimicking concentration variations found in vivo, or of artificially composed patterns. The system comprises a microfluidic device and a motorized computer-controlled scanning stage that has micrometer precision. The device contains a varied number of channels which start in individual sample reservoirs and exit as a closely packed array into an open volume. By loading the sample reservoirs with different solutions, a stripe-patterned flow can be formed outside the channel exits. If a cell is scanned in this patterned flow, its chemical environment can be controlled and varied with high precision. The platform can be used for applications in ion channel research and drug discovery. To confirm this, it was combined with standard patch-clamp equipment, and rapid generation of dose-response curves and sequential stimulation of an ion channel population with different kinds of agonists were demonstrated. Additional possible applications of the system range from elucidation of signalling network properties, to experiments on decoding of temporal signalling patterns that are used by cells. To characterize the stripe-patterned fluid flow, and the diffusion-driven mixing of species within it, fluorescence microscopy and scanning nanoelectrode amperometry were used. The fluid flow and the diffusion of species were modelled with the finite element method, implemented using the commercial software FEMLAB.