Flow and mixing processes in a passive mixing microfluidic chip: Parameters’ estimation and colorimetric analysis

Objectives. The development of microfluidic systems is one of the promising areas of science and technology. In most procedures performed using microfluidic systems, effective mixing in microfluidic channels of microreactors (chips) is of particular importance, because it has an effect on the sensitivity and speed of analytical procedures. The aim of this study is to describe and evaluate the major parameters of the flow and mixing processes in a passive microfluidic micromixer, and to develop an information-measuring system to monitor the dynamics of flow (mixing) of liquids.

Methods. This article provides an overview of the concept of microfluidic mixing chips (micromixers) and their classification, and analyzes the kinds of points of mixing and microfluidic channels for mixing. The article presents the description and calculations of the hydrodynamic similarity criteria (Reynolds, Dean and Peclet numbers), which are the critical parameters for creating and optimizing micromixers (for example, straight and curved channels in the flow rate range between 100 and 1000 µl/min). We have developed an information-measuring system to monitor the dynamics of flow (mixing) of liquids in a microfluidic channel, which consists of a microscope with a digital eyepiece (LOMO MIB, Russia), an Atlas syringe pump (Syrris Ltd., UK) and a passive mixing microfluidic chip of interest (made of clear glass). This system was designed to quickly illustrate the principles of mixing in microfluidic channels of different configurations.

Results. The developed system has allowed carrying out a colorimetric analysis of the modes and dynamics of mixing two liquids (5% aqueous solution of azorubine dye and water) at the T-shaped mixing point, at the straight and curved (double-bend shaped) sections of the microfluidic channel of the passive-type micromixer with flow rates varying from 100 to 400 µl/min.

Conclusions. According to the obtained calculations, the share of the advective mixing processes (formation of vortex flows and increase in the contact area of the mixed substances) in flowing liquids is significantly higher in curved microchannels. The developed information-measuring system to monitor the dynamics of flow (mixing) of liquids in a microfluidic channel is a convenient tool for optimizing the mixing modes in the channels of micromixers, and for designing new configurations of channels in microchips. It would allow intensifying processes and increasing the performance of microfluidic systems.

1. Sackmann E.K., Fulton A.L., Beebe D.J. The present and future role of microfluidics in biomedical research. Nature. 2014;507(7491):181-189. https://doi.org/10.1038/nature13118

2. Manz A., Graber N., Widmer H.M. Miniaturized total chemical-analysis systems-A novel concept for chemical sensing. Sens. Actuator B - Chem. 1990;1:244-248. https://doi.org/10.1039/b907652m

3. Reyes D.R., Iossifidis D., Auroux P.A., Manz A. Micro total analysis systems. 1. Introduction, theory, and technology. Anal. Chem. 2002;74(12):2623-2636. https://doi.org/10.1021/ac0202435

4. Demello A.J. Control and detection of chemical reactions in microfluidic systems. Nature. 2006;442(7101):394-402. https://doi.org/10.1038/nature05062

5. Hessel V., Löb P., Krtschil U., Löwe H. Microstructured reactors for development and production in pharmaceutical and fine chemistry. Ernst Schering Found Symp. Proc. 2006;3:205-240. https://doi.org/10.1007/2789_2007_035

6. Samiei E., Tabrizian M., Hoorfar M. A review of digital microfluidics as portable platforms for lab-on-a-chip applications. Lab Chip. 2016;16(13):2376-2396. https://doi.org/10.1039/c6lc00387g

7. Mou L., Jiang X. Materials for microfluidic immunoassays: A review. Adv. Healthcare Mater. 2017;6(15):1-20. https://doi.org/10.1002/adhm.201601403

8. Yáñez-Sedeño P., Campuzano S., Pingarrón J.M. Multiplexed electrochemical immunosensors for clinical biomarkers. Sensors (Basel). 2017;17(5):1-30. https://doi.org/10.3390/s17050965

9. Mancera-Andrade E.L., Parsaeimehr A., Arevalo-Gallegos A., Ascencio-Favela G., Parra-Saldivar R. Microfluidics technology for drug delivery: A review. Front Biosci. (Elite Ed.). 2018;10:74-91. https://doi.org/10.2741/e809

10. Kimura H., Sakai Y., Fujii T. Organ/body-on-a-chip based on microfluidic technology for drug discovery. Drug Metabolism and Pharmacokinetics. 2018;33(1):43-48. https://doi.org/10.1016/j.dmpk.2017.11.003

11. Ottino J.M., Wiggins S. Introduction: Mixing in microfluidics. Phil. Trans. R. Soc. Lond. A. 2004;362:923-935. https://doi.org/10.1098/rsta.2003.1355

12. Chin P., Barney W.S., Pindzola B.A. Microstructured reactors as tools for the intensification of pharmaceutical reactions and processes. Curr. Opin. Drug Discov. Devel. 2009;12(6):848-861.

13. Nguyen N.T., Wu Z. Micromixers - a review. J. Micromech. Microeng. 2005;15:R1-R16. https://doi.org/10.1088/0960-1317/15/2/R01

14. Cai G., Xue L., Zhang H., Lin J. A review on micromixers. Micromachines (Basel). 2017;8(9):E274. https://doi.org/10.3390/mi8090274

15. Soleymani A., Kolehmainen E., Turunen I. Numerical and experimental investigations of liquid mixing in T-type micromixers. Chem. Eng. J. 2008;135:S219-S228. https://doi.org/10.1016/j.cej.2007.07.048

16. Sudarsan A.P., Ugaz V.M. Multivortex micromixing. Proc. Natl. Acad. Sci. USA. 2006;103(19):7228-7233. https://doi.org/10.1073/pnas.0507976103

17. Nizkaya T.V., Asmolov E.S., Vinogradova O.I. Advective superdiffusion in superhydrophobic microchannels. Phys. Rev. E - Statistical, Nonlinear, and Soft Matter Physics. 2017;96:033109. https://doi.org/10.1103/PhysRevE.96.033109

18. Kukhtevich I.V., Posmitnaya Ya.S., Belousov K.I., Bukatin A.S., Evstrapov A.A. Principles, technologies and droplet-based microfluidic devices. Part 1 (Review). Nauchnoe Priborostroenie = Scientific Instrumentation. 2015;25(3):65-85 (in Russ.). https://doi.org/10.18358/np-25-3-i6585

19. Chernykh V.Ya., Sarbashev K.A., Shulenini A.V., Zhirnova E.V. Determination of the color characteristics of wheat flour in the production of bread and pasta. Khleboproducty [Bakery products]. 2017;(2):44-47 (in Russ.).

20. Rudyak V.Ya., Belkin A.A., Egorov V.V., Ivanov D.A. Simulation of flows in nanochannels by the molecular dynamics method. Nanosistemy: fizika, khimiya, matematika = Nanosystems: Physics, Chemistry, Mathematics. 2011;2(4):100-112 (in Russ.).

21. Nizkaya T.V., Asmolov E.S., Zhou J., Schmid F., Vinogradova O.I. Flows and mixing in channels with misaligned superhydrophobic walls. Phys. Rev. E. 2015;91(3):033020. https://doi.org/10.1103/PhysRevE.91.033020

22. am Ende M.T., am Ende D.J. Chemical Engineering in the Pharmaceutical Industry: Drug Product Design, Development, and Modeling. New York: John Wiley & Sons, 2019. 688 p.