Normally-closed dispensing valve and in-line pressure and flow sensor fabricated in low-cost polymer technology

Abstract: The presented thesis pursues the development of a smart single-use liquid handling system, which enables the dosage of small quantities of liquids in the microliter range with high precision and an online sensor control. Three components are developed within this thesis: a low-cost solenoid dispensing valve and a single-use pressure and flow sensor. All liquid carrying parts of these components are fabricated in low-cost polymer technology so that they can be easily exchanged after use to avoid costly cleaning steps.

The low-cost solenoid dispensing valve is fabricated by injection molding. Theoretical models are developed to calculate the acting forces in the valve, allowing the fabrication of a small valve including coil (dout < 9mm), which enables parallel processing of 96-well plates, and thereby featuring low actuation currents (IPeak = 0.16 A) at a power consumption P of 3.8 W. The dosing performance of the solenoid valve is characterized in a volume range from 0.6 μL to 10. The valve demonstrates outstanding performance for water with intra-run CV ranging from 0.2% to 4.8%. The single-use valve presented achieves comparable performance to existing high-precision non-disposable dispensing valves at significantly lower material costs (<1€).

A low-cost capacitive pressure sensor is developed for dynamic in-line pressure measurement of liquids between 0mbar and 350 mbar, whereby the material costs for the disposable parts could be kept below 1€. The sensor prototype with the most flexible measuring cell has a sensitivity of 0.0135V/mbar with a corresponding linear correlation coefficient of R(x, y) = 0.996. The sensor resolution is 16 mbar for pressures below 30 mbar and 5 mbar for a pressure range between 30 mbar and 350 mbar. The total sensor accuracy AccRSS is 4.0% of Full Scale Output (FSO). Of particular note is the average load-to-load CV of 7.8% as the elastic sensing element was removed and reinstalled between the electrodes of the sensor prior to each measurement. This demonstrates that the intended use of a single-use sensing element and reusable electronics electrode and amplifier is achievable with adequate reproducibility. Additionally, the pressure sensor allows real-time sensing of highly dynamic pressure changes such as those encountered in liquid handling systems, as demonstrated experimentally here for a solenoid dispensing valve (tres < 4.5 ms).

As a third component, a single-use flow sensor based on the differential pressure principle is developed. It is composed of two pressure sensors presented before and a capillary module acting as fluidic resistance in between. It is successfully characterized from 0 to 50 μL/s resulting in a total sensor accuracy AccRSS of 4.5%FSO and a resolution of 0.4 μL/s. A mathematical approximation between the measured pressure drop and the calculated flow rate is derived. The maximum deviation between the calculated flow rate in dependency of the measured pressure drop and the measured flow rate with the reference sensor is 4.1%FSO (at 10 μL/s).

For closed-loop controlled dispensing, the precision of the solenoid dispensing valve is ensured by an active real-time control of the actuation time dependent on the actual flow rate during the dispense. The achieved precision (CV) of five runs is between 0.6% and 2.0%. There is also a linear relationship between the target volume and the measured mean volume for loop-controlled dispensing performance. However, the measured volume shows an offset of average 0.8 μL compared to the target volume. This offset results from the closing behavior of the dispensing valve. After the current is turned off, it takes about 4.8 ms until the valve is completely closed. This increased opening time corresponds to an additional dispensed volume. Overall, a disposable dispensing valve, pressure sensor and flow sensor, which can be used individually or combined modularly, have been successfully manufactured. These interchangeable single-use components will enable dispensing applications to be more affordable and hygienic, making them attractive to the life science sector as they combine high-precision volumetric dispensing with cost efficiency and ease of use

Objekt anzeigen

• Standort: Deutsche Nationalbibliothek Frankfurt am Main
• Umfang: Online-Ressource
• Sprache: Englisch
• Anmerkungen: Universität Freiburg, Dissertation, 2021

Klassifikation und Themen

• Schlagwort: Pressure ; Cost ; Technology ; Dispensieren ; Magnetventil ; Drucksensor ; Durchflusssensor ; Regelungssystem

Beteiligte, Orts- und Zeitangaben

• Ereignis: Veröffentlichung
• (wo): Freiburg
• (wer): Universität
• (wann): 2021
• Urheber: Kartmann, Sabrina
• Beteiligte Personen und Organisationen: Zengerle, Roland ; Albert-Ludwigs-Universität Freiburg. Fakultät für Angewandte Wissenschaften

Weitere Informationen

• DOI: 10.6094/UNIFR/219318
• URN: urn:nbn:de:bsz:25-freidok-2193186
• Rechteinformation: Kein Open Access; Der Zugriff auf das Objekt ist unbeschränkt möglich.