A microfluidic chemostat integrated with a cell sorter, which we call a "sort-o-stat", will enable more complicated selections to be applied to a population of cells in continuous culture. In particular, time varying selective pressures as well as very specific selection strengths can be applied. We will evaluate whether or not these more sophisticated selective pressures will be of practical use in service of evolving engineered biological systems. Selection can be based on any characteristic that can be reliably measured via microscopy. Lastly, since this is a physical selection (rather than a chemical one), it may be more difficult for cells to find unexpected methods to evade selection.
The design of the Sortostat is an extension of the microchemostat design created by Frederick Balagadde. (REF)
This section describes common failure points to help in debugging.
- Apply too high of a dilution rate too quickly
- usually a good idea to grow the cells with a very low dilution rate (e.g. D=0.05) for ~10hrs in order to ensure that the cells are growing well and that there are no problems with the chip. If the cells grow well then you can increase the dilution rate.
- Cells escaping from the sorting chamber
- This can happen as a result of closing both the ClockWise and CounterClockWise valves, resulting in a pressure build up in the chambers between push-UP valves. It is not clear how pervasive a problem this is, but I have made changes to the Microfluidic chemostat labview program to close the CW and CCW sequentially to help the problem.
- Cells stop producing fluorescent proteins
- O2 transfer in the chip
- After growing cells for ~1 week in the reactor the growth rate begins to slow and the cells proceed slowly towards washout. We suspect this is due to oxygen transfer issues in the chip though we are in the process of confirming that as the source of the problem.