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All cells in our bodies are exposed to mechanical stimuli. For some of these cells, such as endothelial cells, it has been shown that their proper function depends on mechanical stimuli. While cells investigated in vivo are usually exposed to natural mechanical stimuli, cells studied in vitro often lack them. In order to provide realistic mechanical stimuli in vitro, cells or tissues can be placed within devices termed flow chambers, flow cells, perfusion cells or bioreactors, and exposed to flow generated by a pumping system, typically a peristaltic pump (Figure 1), or a rotating disk. The level of mechanical stimulus – expressed as shear stress, strain and pressure – is varied by adjusting the flow rate and dimensions of the flow device.

Well-controlled flow generation is an integral part of the flow system design. Current systems depend mostly on peristaltic or syringe pumps which either introduce unwanted oscillations or are unable to accurately reproduce physiologic flow waveforms. During previous semesters, successive student projects have led to novel gas actuated pump systems in which flow is forced to pass through a flow chamber between two reservoirs by controlling the gas pressure within the reservoirs. However these systems are either unable to provide continuous operation for flows with a non-zero mean (Figure 2), or rely on a peristaltic or turbodynamic backflow pump (Figure 3) to ensure that no reservoir empties as a result of mean fluid outflow. This pump introduces new unwanted oscillations which prevent the system from providing accurate flow control.

To provide continuous operation exclusively through the use of pressurized reservoirs we have designed a new approach. The goal of this project is to implement and investigate such a system.

During the course of this project, a new pump system based on a cross-switching mechanism for the flow path (Figure 4) was successfully created. The system was evaluated and we found that some disturbances occur during the switching of the flow path. The causes of these disturbances were investigated and possible solutions were proposed. These solutions will be explored in a future project.