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Miniaturization of microfluidic control systems for high-pressure chromatography
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science and Engineering, Microsystems Technology.ORCID iD: 0000-0002-4824-8908
2024 (English)Doctoral thesis, comprehensive summary (Other academic)
Description
Abstract [en]

This thesis explores flow control and sensing in microfluidic chips for high-pressure applications. Sub-cm glass chips have been designed and fabricated with the aim of miniaturizing chemical analysis systems. Today, chemical analyses are performed worldwide for medical and environmental purposes. As more tests become available for a wider audience, the demand further increases. The large instruments that are typically used are expensive and have high chemical and power consumption. Miniaturizing components has, on the contrary, the ability to decrease volumes, costs, and environmental impacts. In addition to lower consumption, miniaturization carries several features: quick heat distribution, laminar flow, and higher pressure tolerances, to name a few. In this thesis, microfluidic chips are developed aiming to replace larger-scale instruments. Applications are centered around high-performance chromatography, which is a separation method used to separate and detect compounds in a sample. Different flow phenomena are also investigated, including fluid compressibility and capacitance, which become interesting when working at elevated pressures. Experiments have been made showing how this impacts the regulation of microfluidic flow. Thermal regulation of viscosity has been a centerpiece of this work. Controlling flow rate and pressure in a system by changing the viscosity of a fluid has proven effective for several applications. This was utilized to maintain back pressure at the end of a system as well as to control and stabilize flow at the beginning. It was also used to regulate composition and adjust parallel flows during experiments. Multiple chips were also connected to utilize several features and to get close to fully miniaturized and portable analysis systems. Apart from flow actuation, the microfluidic chips were also equipped with sensors for accurate sensing in close proximity.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2024. , p. 58
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 2408
Keywords [en]
High pressure, Microfluidics, Thermal regulation, Chromatography, Fluid mechanics
National Category
Materials Engineering Fluid Mechanics and Acoustics
Research subject
Engineering Science with specialization in Microsystems Technology
Identifiers
URN: urn:nbn:se:uu:diva-527206ISBN: 978-91-513-2147-9 (print)OAI: oai:DiVA.org:uu-527206DiVA, id: diva2:1854514
Public defence
2024-06-13, Lecture hall Eva von Bahr, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 09:15 (English)
Opponent
Supervisors
Available from: 2024-05-22 Created: 2024-04-25 Last updated: 2024-05-22
List of papers
1. A microfluidic control board for high-pressure flow, composition, and relative permittivity
Open this publication in new window or tab >>A microfluidic control board for high-pressure flow, composition, and relative permittivity
2018 (English)In: Analytical Chemistry, ISSN 0003-2700, E-ISSN 1520-6882, Vol. 90, no 21, p. 12601-12608Article in journal (Refereed) Published
Abstract [en]

Flow control is central to microfluidics and chromatography. With decreasing dimensions and high pressures, precise fluid flows are often needed. In this paper, a high-pressure flow control system is presented, allowing for the miniaturization of chromatographic systems and the increased performance of microfluidic setups by controlling flow, composition and relative permittivity of two-component flows with CO2. The system consists of four chips: two flow actuator chips, one mixing chip and one relative permittivity sensor. The actuator chips, throttling the flow, required no moving parts as they instead relied on internal heaters to change the fluid resistance. This allows for flow control using miniaturized fluid delivery systems containing only a single pump or pressure source. Mobile phase gradients between 49% to 74% methanol in CO2 were demonstrated. Depending on how the actuator chips were dimensioned, the position of this range could be set for different method-specific needs. With the microfluidic control board, both flow and composition could be controlled from constant pressure sources, drift could be removed, and variations in composition could be lowered by 84%, resulting in microflows of CO2 and methanol with a variation in the composition of 0.30%.

National Category
Chemical Engineering
Identifiers
urn:nbn:se:uu:diva-353953 (URN)10.1021/acs.analchem.8b02758 (DOI)000449722500039 ()30269500 (PubMedID)
Funder
Knut and Alice Wallenberg Foundation
Available from: 2018-06-19 Created: 2018-06-19 Last updated: 2024-04-25Bibliographically approved
2. 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: 2024-04-25Bibliographically approved
3. 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: 2024-04-25Bibliographically approved
4. 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: 2024-04-25Bibliographically approved
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