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Miniaturized fluid system for high-pressure analytics
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science and Engineering, Microsystems Technology.
2024 (English)Doctoral thesis, comprehensive summary (Other academic)
Description
Abstract [en]

High-pressure chemistry can be used to determine the contents of blood or water samples and to discover new chemistries. However, working with chemistry at pressures of many tens, or even hundreds, of bars often requires expensive and stationary equipment, such as autoclaves or chromatographic systems like high-performance liquid chromatography (HPLC).

Since the introduction of microfluidics in the '90s, researchers have attempted to develop microfluidic chips as microreactors to speed up synthesis with faster mass and heat transfer. Other researchers have made efforts to create microfluidic chip-based HPLC to reduce the cost, increase the separation quality, speed up the analysis, and even enable portable systems for on-site medical or environmental analysis. Still, fully integrated systems have not yet been realized due to a lack of fluidic control components.

This thesis presents novel methods for on-chip regulation and monitoring of pressure, flow, and temperature. Papers I and II specifically suggest a method for regulating backpressure and stabilizing pressure and flows using thermally controlled restrictors. Furthermore, a collaboration was made where a pressure-regulating chip was connected to an on-chip HPLC. The purpose of this was to activate sample plugs and therefore reduce the requirement for expensive surrounding equipment and enable portability, Paper III. Paper IV explores the use of a pressurized capsule to generate high-pressure flows that are coupled to a pressure-regulating chip to stabilize and regulate the pressure. Finally, an approach for integrating pressure sensors into high-pressure tolerant microchannels has been proposed, Paper V.

The work conducted has provided new insights into fluid dynamics. The regulating method employed in Paper I-IV utilizes a restrictor that alters the pressure drop as temperature changes, hence changing the viscosity of the fluid. Although this technology has been known since before, new understandings have emerged regarding how the compressibility of incompressible fluids must be considered at higher pressures. Additionally, the concept of buffer capacitance is presented, which is central when working with high-pressure microfluidics.

Through this thesis, discoveries of high-pressure microfluidics have been accomplished, which enable micro-total-analysis systems that could serve as portable HPLC equipment.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2024. , p. 60
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 2366
Keywords [en]
High-pressure, Microfluidics, Thermal regulation, Fluid mechanics, In-situ sensors, High-pressure analytics
National Category
Fluid Mechanics and Acoustics Materials Engineering
Research subject
Engineering Science with specialization in Microsystems Technology
Identifiers
URN: urn:nbn:se:uu:diva-523408ISBN: 978-91-513-2038-0 (print)OAI: oai:DiVA.org:uu-523408DiVA, id: diva2:1838670
Public defence
2024-04-05, Häggsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 10:15 (English)
Opponent
Supervisors
Available from: 2024-03-13 Created: 2024-02-18 Last updated: 2024-03-13
List of papers
1. Thermally controlled microfluidic back pressure regulator
Open this publication in new window or tab >>Thermally controlled microfluidic back pressure regulator
2022 (English)In: Scientific Reports, E-ISSN 2045-2322, Vol. 12, no 1, article id 569Article in journal (Refereed) Published
Abstract [en]

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.

Place, publisher, year, edition, pages
NATURE PORTFOLIO, 2022
Keywords
SUPERCRITICAL-FLUID: CHROMATOGRAPHY; LIQUID-CHROMATOGRAPHY: FLOWSYSTEM: HPLC; SEPARATION
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:uu:diva-466637 (URN)10.1038/s41598-021-04320-6 (DOI)000742155800057 ()35022424 (PubMedID)
Available from: 2022-01-31 Created: 2022-01-31 Last updated: 2024-02-18Bibliographically approved
2. Microfluidic active pressure and flow stabiliser
Open this publication in new window or tab >>Microfluidic active pressure and flow stabiliser
2021 (English)In: Scientific Reports, E-ISSN 2045-2322, Vol. 11, article id 22504Article in journal (Refereed) Published
Abstract [en]

In microfluidics, a well-known challenge is to obtain reproducible results, often constrained by unstable pressures or flow rates. 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 this work, a novel stabilisation method that is able to handle high pressures in microfluidics is presented. It is based on upstream flow capacitance and thermal control of the fluid's viscosity through a PID controlled restrictor-chip. The stabiliser consists of a high-pressure-resistant microfluidic glass chip with integrated thin films, used for resistive heating. Thereby, the stabiliser has no moving parts. The quality of the stabilisation was evaluated with an ISCO pump, an HPLC pump, and a Harvard pump. 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. Poor accuracy of a pump was compensated for in the control algorithm, as it otherwise reduced the capacity to stabilise longer times. 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. By this work, a new approach to improve the control of microfluidic systems has been achieved.

Place, publisher, year, edition, pages
Springer NatureSpringer Nature, 2021
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:uu:diva-461143 (URN)10.1038/s41598-021-01865-4 (DOI)000720520100014 ()34795333 (PubMedID)
Funder
The Kamprad Family Foundation
Note

De två första författarna delar förstaförfattarskapet.

Available from: 2021-12-13 Created: 2021-12-13 Last updated: 2024-02-18Bibliographically approved
3. Coupling microchip pressure regulators with chipHPLC as a step toward fully portable analysis system
Open this publication in new window or tab >>Coupling microchip pressure regulators with chipHPLC as a step toward fully portable analysis system
Show others...
2023 (English)In: Sensors and actuators. B, Chemical, ISSN 0925-4005, E-ISSN 1873-3077, Vol. 385, article id 133732Article in journal (Refereed) Published
Abstract [en]

Herein the coupling of a miniaturized, nanoliter scaled, pressure regulator (chipPR), and a chipHPLC device is introduced. The active temperature based flow control of the chipPR is able to generate rapid pressure changes and therefore enables on-chip pinched injection and flow gradients with reduced instrumental effort and minimal dead volumes. The functionality of the chipPR empowered chipHLPC device was demonstrated with high-speed HPLC-separations applying fluorescence and electrospray mass spectrometry (ESI-MS) detection. The system shows excellent long-term stability of chromatography integrity (retention times with RSD of 0.44-0.91%) due to the integration of a PID feedback regulation. This first chip-based HPLC device equipped with chipPRs enables precise flow control with significantly reduced technical effort compared to the state-of-the-art.

Place, publisher, year, edition, pages
Elsevier, 2023
Keywords
Lab-on-a-chip, ChipHPLC, Thermal actuation, Microfluidics, Pressure regulation
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering Analytical Chemistry
Identifiers
urn:nbn:se:uu:diva-502526 (URN)10.1016/j.snb.2023.133732 (DOI)000977773900001 ()
Funder
The Kamprad Family Foundation, 20170169
Available from: 2023-05-26 Created: 2023-05-26 Last updated: 2024-02-18Bibliographically approved
4. Portable high-pressure pump system for HPLC combining pressurized gas and on-chip pressure regulation
Open this publication in new window or tab >>Portable high-pressure pump system for HPLC combining pressurized gas and on-chip pressure regulation
(English)Manuscript (preprint) (Other academic)
Abstract [en]

High-pressure pumps for microfluidic systems typically require high powerand have large sizes, which hinder portability of otherwise miniaturized HPLC systems. To solve this, a battery-powered, pneumatic system for pressure-driven chromatography is presented. The system utilizes the stored energy in pressurized gas without consuming any of the gas. As the chromatography liquid flows, the gas in the pressure container expands and its pressure reduces. To compensate for this, a solution is presented with an on-chip microfluidic pressure regulator. The chip contains a microfluidic restrictor where fluid is heated by Joule heating to decrease viscosity, and thus reduce the pressure drop over the restrictor. An 18 V battery driven system with 50 ml N2 at 51 bar could provide a water flow rate of 55 µl/min at 32 bar for 67 min with a mean power consumption of 0.2 W. With the regulating microfluidic chip, the pressure stability was 2 mbar, i.e., on pair with high-quality high-pressure syringe pumps. The required gas volume, and hence the total size, is scalable with the desired liquid volume, which makes it suitable for miniaturized systems.

National Category
Other Materials Engineering Fluid Mechanics and Acoustics
Research subject
Engineering Science with specialization in Microsystems Technology
Identifiers
urn:nbn:se:uu:diva-523406 (URN)
Available from: 2024-02-18 Created: 2024-02-18 Last updated: 2024-02-19Bibliographically approved
5. In-line small high-pressure sensors in anodically bonded microfluidic restrictors
Open this publication in new window or tab >>In-line small high-pressure sensors in anodically bonded microfluidic restrictors
2023 (English)In: Sensors and Actuators A-Physical, ISSN 0924-4247, E-ISSN 1873-3069, Vol. 356, article id 114345Article in journal (Refereed) Published
Abstract [en]

High-pressure microflow chemistry is advancing due to its potential advantages of being rapid, inexpensive, and accessible. However, as microfluidic devices gain popularity in areas such as synthesis and analysis, there is still a lack of control over thermodynamic parameters during high-pressure processes. This is an effect of existing external sensors causing an excessive increase in the system's internal and dead volumes. To avoid this, more sensors need to be integrated into high-pressure-resistant microfluidic channels. Herein, a proposed approach for integrating an in-line pressure-flow-temperature sensor is provided, where the flow is calculated from the pressure drop over a restrictor. An anodically bonded Si-glass microfluidic chip was constructed with wet-etched glass channels, boron-doped piezoresistors, and dry-etched diaphragms. The pressure sensors showed a precision of +/- 0.07% of full scale (70 bar) and the chip can withstand more than 210 bar. The internal volume was 25 nL and the diaphragms measured 72 x 108 mu m. With this work, improved control of high-pressure microfluidics has been accomplished.

Place, publisher, year, edition, pages
ELSEVIER SCIENCE SA, 2023
Keywords
High-pressure microfluidics, Diaphragm pressure sensor, Piezoresestivity, Micro total analysis system, Process control
National Category
Energy Engineering
Identifiers
urn:nbn:se:uu:diva-506963 (URN)10.1016/j.sna.2023.114345 (DOI)001002776000001 ()
Funder
The Kamprad Family Foundation, 20170169
Available from: 2023-07-04 Created: 2023-07-04 Last updated: 2024-02-18Bibliographically approved

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