Techniques to manipulate the environment around and inside single cells

Doctoral thesis, 2008

Several methods for extending the functionality of a commercially available microfluidic system have been developed to allow for the manipulation of the extracellular and intracellular environments. The microfluidic system generates a chemically patterned laminar flow in an open volume. Objects, such as electrodes or cells, scanned through the patterned flow sequentially experience different solution environments with millisecond solution exchange times. The original device offered the advantages of access to numerous solution environments with rapid, millisecond exchange times and had proven useful in ion channel screening. The developments in this thesis allow for the delivery of complex input patterns, both in and around cells, with the possibility to update exposure patterns over time, facilitating an unprecedented level of control over the cellular environment both in terms of solution composition and temperature. In order to mimic physiologically observed oscillations, algorithms for waveform creation were devised, which allow for the generation and emulation of complex variations in the concentration of substances on relevant time (i.e. ms-to-minutes) and length scales (i.e. around sub-micrometer-to-micrometer-sized objects such as single organelles and single cells). By incorporating valves to switch between different input solutions in each flow segment, the laminar flow pattern can be updated over time. This allows for access to a greater number of different solutions, as well as the possibility of mixing solutions on-chip. Addition of resistive heating coils facilitates control of the temperature during experiments to study temperature-dependent effects and to obtain thermodynamic information such as activation energies. To control the intracellular chemistry within whole cells, in order to generate intracellular waveforms or gradients as well as screen and titrate intracellular enzymes and receptors in an in situ environment, the microfluidic system was combined with a chemical method for increasing the cell membrane permeability. The modified system(s), presented in this thesis have many biological applications, including receptor screening, investigation of receptor kinetics and studies of signaling pathways and oscillations. This system would also be useful in any application where a high degree of control over exposure patterns is required. Additionally, the development strategies described here could easily be applied to extend the function of other microfluidic devices.