Thermally controlled microfluidic back pressure regulator

Karolina Svensson,Klas Hjort,Simon Södergren

doi:10.1038/s41598-021-04320-6

Karolina Svensson, Klas Hjort + Show 1 more

Open Access

https://doi.org/10.1038/s41598-021-04320-6

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Abstract

By using the temperature dependence of viscosity, we introduce a novel type of microfluidic lab-on-a-chip back pressure regulator (BPR) that can be integrated into a micro-total-analysis-system. A BPR is an important component used to gain pressure control and maintain elevated pressures in e.g. chemical extractions, synthesis, and analyses. Such applications have been limited in microfluidics, since the back pressure regularly has been attained by passive restrictors or external large-scale BPRs. Herein, an active microfluidic BPR is presented, consisting of a glass chip with integrated thin-film heaters and thermal sensors. It has no moving parts but a fluid restrictor where the flow resistance is controlled by the change of viscosity with temperature. Performance was evaluated by regulating the upstream pressure of methanol or water using a PID controller. The developed BPR has the smallest reported dead volume of 3 nL and the thermal actuation has time constants of a few seconds. The pressure regulation were reproducible with a precision in the millibar range, limited by the pressure sensor. The time constant of the pressure changes was evaluated and its dependence of the total upstream volume and the compressibility of the liquids is introduced.

Highlights

By using the temperature dependence of viscosity, we introduce a novel type of microfluidic lab-ona-chip back pressure regulator (BPR) that can be integrated into a micro-total-analysis-system
By adjusting the flow restriction and thereby the pressure drop over the BPR, the pressure at its inlet can be controlled. This allows a system with low flow restriction to be kept at elevated pressure, and ensures that it will not drop below the set level of the BPR
A pressure drop through the BPR chip was experimentally measured to 70 bar, using methanol at 20 °C and 40 μL/min, corresponding to a channel depth of 8.8 μm

Summary

Introduction

By using the temperature dependence of viscosity, we introduce a novel type of microfluidic lab-ona-chip back pressure regulator (BPR) that can be integrated into a micro-total-analysis-system. A BPR is an important component used to gain pressure control and maintain elevated pressures in e.g. chemical extractions, synthesis, and analyses Such applications have been limited in microfluidics, since the back pressure regularly has been attained by passive restrictors or external large-scale BPRs. an active microfluidic BPR is presented, consisting of a glass chip with integrated thin-film heaters and thermal sensors. The simplest method is to use a capillary with high restriction where the length and diameter are adjusted to reach the desired pressure drop. As simple as it is, it has to be adjusted for every change in flow rate, temperature or composition. There are more complex mechanical BPRs where the set level can be changed, mechanical BPRs need a certain inner volume as it is crucial for their working principle

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