A combination of high-tolerance micro components that control the flow of gas into and out of the pressure chamber and an innovative control algorithm that adapts to system characteristics achieves ultra-precise pulseless flow control. The flow-rate precision benefits the fields of droplet generation, micro process engineering and microreaction kinetics.
Closed-loop flow control enables users of the Mitos P-Pump from UK-based microfluidics expert Dolomite, which has an office in Charlestown, Mass., to select flow rates between 70 nl/min and 5 ml/min instead of relying on pressure settings. The gas pressure inside the chamber is then automatically adjusted to meet the target flow rate. This is achieved by positioning a flow rate sensor in line, which constantly sends flow rate measurements back to the pump. The pump processes the information and makes adjustment decisions. According to Dolomite’s long-term tests in the flow control mode, a coefficient of variation (CV) of less than 0.14 percent for the droplet size can be achieved over extended periods.
“The key benefit of flow control mode over pressure control mode is that it can compensate for small changes in the system flow resistance to maintain constant droplet size,” notes mechanical engineer Tim Aktins, who designed the Mitos P-Pump. “In theory, in a perfect system, the pressure control mode can give equally good CV compared to flow control mode. In practice, however, small changes in system flow resistance over long time periods can be anticipated with pressure control, which makes flow control mode the better (mode).”
Benefits Over Syringe Pumps
Dolomite’s pressure-driven Mitos P-Pump system (in either flow control mode or pressure control mode) is said to give significant benefits over a syringe-based system. The company’s own tests have demonstrated that the pulsations introduced to the flow by a syringe pump’s stepper motor drive give rise to droplet size variability. Mean droplet diameter with the Mitos P-Pump was 99.7 µm with a standard deviation of 0.6 µm, compared with a mean droplet diameter of 93.4 µm and a standard deviation of 5.1 µm for a market-leading syringe pump. Meanwhile, CV was 0.6 percent compared with 5.5 percent for the syringe pump.
The Mitos P-Pump can potentially handle any fluids, as the wetted materials are the user-selected vial (typically glass) and dip tube (typically FEP or PTFE plastic). The vial can be placed directly in the chamber. Due to the wide pressure capability (0 to 10 bar), the pump can handle high-viscosity (more than 100 Cp) liquids. With the correct setup, it is also possible to use the pump to deliver low-viscosity fluids, such as gases.
By connecting a Mitos flow rate sensor in line between the pump and microfluidic device, users can enter a flow rate target directly on the Mitos P-Pump itself with no need for a personal computer. This simplifies the setup for the user and makes it possible to switch seamlessly between pressure control and flow control modes from a single user interface. Onboard controls are ideal for a lab-based environment, where space is limited, according to Dolomite.
A personal computer application is also available, which can control multiple pump and flow sensor units simultaneously and independently and thereby manage complex experiments. The software package also provides graphical interfaces for viewing the pressures and flow rates over time. Quick changeover between flow control and pressure control is also enabled with the software package, and users can continue to benefit from the flow smoothness of the pressure-driven Mitos P-Pump, but with even more accurate control over the delivery of picoliter reagent volumes into the system, according to Dolomite.
The fields of droplet generation, cell-based studies, fluid-fluid contacting, micro process engineering and microreaction kinetics stand to benefit from the new pump’s performance. In particular, droplet microfluidics, which is a wide field encompassing food emulsions, drug discovery, droplet polymerase chain reaction and biochemical analysis, is a highly promising application target for the Mitos P-Pump. The low-flow-rate capabilities of the pump, meanwhile, are beneficial for generation of small droplets (less than 30 µm dia), which is useful for encapsulating biological matter into droplets as well as introducing picoliter volumes of reagents into microreactors.