However, the active systems suffer from large volumes while the smaller, passive, restrictors cannot handle fluctuations but only noise. There are several reported solutions for different applications in, e.g., low-pressure 3, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18 and high-pressure 19 liquid systems, high-pressure gas systems, and as HPLC pulse dampers 20, 21. To also control the fluctuations, active systems can use electro-pneumatics. To reduce the noise, passive systems use either a flexible channel or membrane, or a non-flexible restrictor. Today, there are different types of stabilisers available. Using stabilisers and sensors directly connected to the experiment are therefore important for precise control. Further, for pumps with flow rate control, long stabilisation times cause gradients of the flow rate through the experiment. Examples requiring stable flow include high pressure synthesis 1, precise extractions 2, droplet formation 3, and more reproducible separation and sensitive detection in chromatography 4, 5, 6.įor pumps that show the correct pressure level, there can still be components like filters and tubes with varying restrictions, changing the pressure before it reaches the experiment. In demanding applications and for the highest stability, also high pressure syringe pumps or pumps with already integrated dampers suffer from too high noise or long-term fluctuations. Some commonly used pumps, driven by dual pistons or step motors, are known for having a pulsatile behaviour with large fluctuations. It is vital in both micro and macro scale fluidics to provide reliable and reproducible results. By this work, a new approach to improve the control of microfluidic systems has been achieved.Ī pressure or flow stabiliser is a device that reduces fluctuations (low frequency) and noise (high frequency) in a fluidic system. As the dead volume of the stabiliser was only 16 nL, it can be integrated into micro-total-analysis- or other lab-on-a-chip-systems. Poor accuracy of a pump was compensated for in the control algorithm, as it otherwise reduced the capacity to stabilise longer times. The stability was greatly improved for all three pumps, with the ISCO reaching the highest relative precision of 0.035% and the best accuracy of 8.0 ppm. The quality of the stabilisation was evaluated with an ISCO pump, an HPLC pump, and a Harvard pump. Thereby, the stabiliser has no moving parts. The stabiliser consists of a high-pressure-resistant microfluidic glass chip with integrated thin films, used for resistive heating. ![]() ![]() It is based on upstream flow capacitance and thermal control of the fluid’s viscosity through a PID controlled restrictor-chip. In this work, a novel stabilisation method that is able to handle high pressures in microfluidics is presented. Today, there are existing stabilisers made for low-pressure microfluidics or high-pressure macrofluidics, often consisting of passive membranes, which cannot stabilise long-term fluctuations. In microfluidics, a well-known challenge is to obtain reproducible results, often constrained by unstable pressures or flow rates.
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