Open microfluidics

Microfluidics refers to the flow of fluid in channels or networks with at least one dimension on the micron scale.[1][2] In open microfluidics, also referred to as open surface microfluidics or open-space microfluidics, at least one boundary confining the fluid flow of a system is removed, exposing the fluid to air or another interface such as a second fluid.[1][3][4]

Types of open microfluidics

Open microfluidics can be categorized into various subsets. Some examples of these subsets include open-channel microfluidics, paper-based, and thread-based microfluidics.[1][5][6]

Open-channel microfluidics

In open-channel microfluidics, a surface tension-driven capillary flow occurs and is referred to as spontaneous capillary flow (SCF).[1][7] SCF occurs when the pressure at the advancing meniscus is negative.[1] The geometry of the channel and contact angle (θ) of fluids on the surface of the channel can be used to predict whether SCF will occur in the channel by the equation:

 pf/pw < cos(θ)

where pf is the free perimeter of the channel (i.e., the interface not in contact with the channel wall), pw is the wetted perimeter (i.e., the walls in contact with the fluid), and θ is the contact angle of the fluid on the material of the device.[1][5]

Paper-based microfluidics

Paper-based microfluidics utilizes the wicking ability of paper for functional readouts.[8][9] Paper-based microfluidics is an attractive method because paper is cheap, easily accessible, and has a low environmental impact. Paper is also versatile because it is available in various thicknesses and pore sizes.[8] Coatings such as wax have been used to guide flow in paper microfluidics.[10] In some cases, dissolvable barriers have been used to create boundaries on the paper and control the fluid flow.[11] The application of paper as a diagnostic tool has shown to be powerful because it has successfully been used to detect glucose levels,[12] bacteria,[13] viruses,[14] and other components in whole blood.[15] Cell culture methods within paper have also been developed.[16][17] Lateral flow immunoassays, such as those used in pregnancy tests, are one example of the application of paper for point of care or home-based diagnostics.[18] Disadvantages include difficulty of fluid retention and high limits of detection.

Thread-based microfluidics

Thread-based microfluidics, an offshoot from paper-based microfluidics, utilizes the same capillary based wicking capabilities.[19] Common thread materials include nitrocellulose, rayon, nylon, hemp, wool, polyester, and silk.[20] Threads are versatile because they can be woven to form specific patterns.[21] Additionally, two or more threads can converge together in a knot bringing two separate ‘streams’ of fluid together as a reagent mixing method.[22] Threads are also relatively strong and difficult to break from handling which makes them stable over time and easy to transport.[20] Thread-based microfluidics has been applied to 3D tissue engineering and analyte analysis.[23][24]

Advantages

One of the main advantages of open microfluidics is ease of accessibility which enables intervention (i.e., for adding or removing reagents) to the flowing liquid in the system.[25] Open microfluidics also allows simplicity of fabrication thus eliminating the need to bond surfaces. When one of the boundaries of a system is removed, a larger liquid-gas interface results, which enables liquid-gas reactions.[1][26] Open microfluidic devices enable better optical transparency because at least one side of the system is not covered by the material which can reduce autofluorescence during imaging.[27] Further, open systems minimize and sometimes eliminate bubble formation, a common problem in closed systems.[1]

In closed system microfluidics, the flow in the channels is driven by pressure via pumps (syringe pumps), valves (trigger valves), or electrical field.[28] Open system microfluidics enable surface-tension driven flow in channels thereby eliminating the need for external pumping methods.[25][29] For example, some open microfluidic devices consist of a reservoir port and pumping port that can be filled with fluid using a pipette.[1][5][25] Eliminating external pumping requirements lowers cost and enables device use in all laboratories with pipettes.[26]

Disadvantages

Some drawbacks of open microfluidics include evaporation,[30] contamination,[31] and limited flow rate.[4] Open systems are susceptible to evaporation which can greatly affect readouts when fluid volumes are on the microscale.[30] Additionally, due to the nature of open systems, they are more susceptible to contamination than closed systems.[31] Cell culture and other methods where contamination or small particulates are a concern must be carefully performed to prevent contamination. Lastly, open systems have a limited flow rate because induced pressures cannot be used to drive flow.[4]

Applications

Like many microfluidic technologies, open system microfluidics has been applied to nanotechnology, biotechnology, fuel cells, and point of care (POC) testing.[1][4][32] For cell-based studies, open-channel microfluidic devices enable access to cells for single cell probing within the channel.[33] Other applications include capillary gel electrophoresis, water-in-oil emulsions, and biosensors for POC systems.[3][34][35] Suspended microfluidic devices, open microfluidic devices where the floor of the device is removed, have been used to study cellular diffusion and migration of cancer cells.[5] Suspended and rail-based microfluidics have been used for micropatterning and studying cell communication.[1]

References

  1. 1 2 3 4 5 6 7 8 9 10 11 1952-, Berthier, Jean, (2016). Open microfluidics. Brakke, Kenneth A., Berthier, Erwin. Hoboken, NJ: Wiley. ISBN 9781118720936. OCLC 953661963.
  2. ↑ Whitesides, George M. (2006-07). "The origins and the future of microfluidics". Nature. 442 (7101): 368–373. doi:10.1038/nature05058. ISSN 0028-0836. Check date values in: |date= (help)
  3. 1 2 Pfohl, Thomas; Mugele, Frieder; Seemann, Ralf; Herminghaus, Stephan (2003-12-08). "Trends in Microfluidics with Complex Fluids". ChemPhysChem. 4 (12): 1291–1298. doi:10.1002/cphc.200300847. ISSN 1439-4235.
  4. 1 2 3 4 Kaigala, Govind V.; Lovchik, Robert D.; Delamarche, Emmanuel (2012-10-30). "Microfluidics in the "Open Space" for Performing Localized Chemistry on Biological Interfaces". Angewandte Chemie International Edition. 51 (45): 11224–11240. doi:10.1002/anie.201201798. ISSN 1433-7851.
  5. 1 2 3 4 Casavant, B. P.; Berthier, E.; Theberge, A. B.; Berthier, J.; Montanez-Sauri, S. I.; Bischel, L. L.; Brakke, K.; Hedman, C. J.; Bushman, W. (2013-05-31). "Suspended microfluidics". Proceedings of the National Academy of Sciences. 110 (25): 10111–10116. doi:10.1073/pnas.1302566110. ISSN 0027-8424. PMC 3690848.
  6. ↑ Yamada, Kentaro; Shibata, Hiroyuki; Suzuki, Koji; Citterio, Daniel (2017). "Toward practical application of paper-based microfluidics for medical diagnostics: state-of-the-art and challenges". Lab on a Chip. 17 (7): 1206–1249. doi:10.1039/c6lc01577h. ISSN 1473-0197.
  7. ↑ Yang, Die; Krasowska, Marta; Priest, Craig; Popescu, Mihail N.; Ralston, John (2011-09-07). "Dynamics of Capillary-Driven Flow in Open Microchannels". The Journal of Physical Chemistry C. 115 (38): 18761–18769. doi:10.1021/jp2065826. ISSN 1932-7447.
  8. 1 2 Hosseini, Samira; Vázquez-Villegas, Patricia; Martínez-Chapa, Sergio O. (2017-08-22). "Paper and Fiber-Based Bio-Diagnostic Platforms: Current Challenges and Future Needs". Applied Sciences. 7 (8): 863. doi:10.3390/app7080863.
  9. ↑ "Rapid light transmittance measurements in paper-based microfluidic devices". Sensing and Bio-Sensing Research. 5: 55–61. 2015-09-01. doi:10.1016/j.sbsr.2015.07.005. ISSN 2214-1804.
  10. ↑ Müller, R. H.; Clegg, D. L. (1949-09). "Automatic Paper Chromatography". Analytical Chemistry. 21 (9): 1123–1125. doi:10.1021/ac60033a032. ISSN 0003-2700. Check date values in: |date= (help)
  11. ↑ Fu, Elain; Lutz, Barry; Kauffman, Peter; Yager, Paul (2010). "Controlled reagent transport in disposable 2D paper networks". Lab on a Chip. 10 (7): 918. doi:10.1039/b919614e. ISSN 1473-0197. PMC 3228840. PMID 20300678.
  12. ↑ Martinez, Andres W.; Phillips, Scott T.; Carrilho, Emanuel; Thomas, Samuel W.; Sindi, Hayat; Whitesides, George M. (2008-05). "Simple Telemedicine for Developing Regions: Camera Phones and Paper-Based Microfluidic Devices for Real-Time, Off-Site Diagnosis". Analytical Chemistry. 80 (10): 3699–3707. doi:10.1021/ac800112r. ISSN 0003-2700. PMC 3761971. Check date values in: |date= (help)
  13. ↑ Shih, Cheng-Min; Chang, Chia-Ling; Hsu, Min-Yen; Lin, Jyun-Yu; Kuan, Chen-Meng; Wang, Hsi-Kai; Huang, Chun-Te; Chung, Mu-Chi; Huang, Kui-Chou (2015-12). "Paper-based ELISA to rapidly detect Escherichia coli". Talanta. 145: 2–5. doi:10.1016/j.talanta.2015.07.051. ISSN 0039-9140. Check date values in: |date= (help)
  14. ↑ Wang, Hsi-Kai; Tsai, Cheng-Han; Chen, Kuan-Hung; Tang, Chung-Tao; Leou, Jiun-Shyang; Li, Pi-Chun; Tang, Yin-Liang; Hsieh, Hsyue-Jen; Wu, Han-Chung (2014-02). "Immunoassays: Cellulose-Based Diagnostic Devices for Diagnosing Serotype-2 Dengue Fever in Human Serum (Adv. Healthcare Mater. 2/2014)". Advanced Healthcare Materials. 3 (2): 154–154. doi:10.1002/adhm.201470008. ISSN 2192-2640. Check date values in: |date= (help)
  15. ↑ Yang, Xiaoxi; Forouzan, Omid; Brown, Theodore P.; Shevkoplyas, Sergey S. (2012). "Integrated separation of blood plasma from whole blood for microfluidic paper-based analytical devices". Lab Chip. 12 (2): 274–280. doi:10.1039/c1lc20803a. ISSN 1473-0197.
  16. ↑ Tao, Fang Fang; Xiao, Xia; Lei, Kin Fong; Lee, I-Chi (2015-03-18). "Paper-based cell culture microfluidic system". BioChip Journal. 9 (2): 97–104. doi:10.1007/s13206-015-9202-7. ISSN 1976-0280.
  17. ↑ Walsh, David I.; Lalli, Mark L.; Kassas, Juliette M.; Asthagiri, Anand R.; Murthy, Shashi K. (2015-05-18). "Cell Chemotaxis on Paper for Diagnostics". Analytical Chemistry. 87 (11): 5505–5510. doi:10.1021/acs.analchem.5b00726. ISSN 0003-2700.
  18. ↑ Lam, Trinh; Devadhasan, Jasmine P.; Howse, Ryan; Kim, Jungkyu (2017-04-26). "A Chemically Patterned Microfluidic Paper-based Analytical Device (C-µPAD) for Point-of-Care Diagnostics". Scientific Reports. 7 (1). doi:10.1038/s41598-017-01343-w. ISSN 2045-2322.
  19. ↑ Erenas, Miguel M.; de Orbe-Payá, Ignacio; Capitan-Vallvey, Luis Fermin (2016-04-29). "Surface Modified Thread-Based Microfluidic Analytical Device for Selective Potassium Analysis". Analytical Chemistry. 88 (10): 5331–5337. doi:10.1021/acs.analchem.6b00633. ISSN 0003-2700.
  20. 1 2 Reches, Meital; Mirica, Katherine A.; Dasgupta, Rohit; Dickey, Michael D.; Butte, Manish J.; Whitesides, George M. (2010-05-24). "Thread as a Matrix for Biomedical Assays". ACS Applied Materials & Interfaces. 2 (6): 1722–1728. doi:10.1021/am1002266. ISSN 1944-8244.
  21. ↑ Li, Xu; Tian, Junfei; Shen, Wei (2009-12-09). "Thread as a Versatile Material for Low-Cost Microfluidic Diagnostics". ACS Applied Materials & Interfaces. 2 (1): 1–6. doi:10.1021/am9006148. ISSN 1944-8244.
  22. ↑ Ballerini, David R.; Li, Xu; Shen, Wei (2011-03). "Flow control concepts for thread-based microfluidic devices". Biomicrofluidics. 5 (1): 014105. doi:10.1063/1.3567094. ISSN 1932-1058. Check date values in: |date= (help)
  23. ↑ Mostafalu, Pooria; Akbari, Mohsen; Alberti, Kyle A.; Xu, Qiaobing; Khademhosseini, Ali; Sonkusale, Sameer R. (2016-07-18). "A toolkit of thread-based microfluidics, sensors and electronics for 3D tissue embedding for medical diagnostics". Microsystems & Nanoengineering. 2 (1). doi:10.1038/micronano.2016.39. ISSN 2055-7434.
  24. ↑ Erenas, Miguel M.; de Orbe-Payá, Ignacio; Capitan-Vallvey, Luis Fermin (2016-04-29). "Surface Modified Thread-Based Microfluidic Analytical Device for Selective Potassium Analysis". Analytical Chemistry. 88 (10): 5331–5337. doi:10.1021/acs.analchem.6b00633. ISSN 0003-2700.
  25. 1 2 3 Lee, Jing J.; Berthier, Jean; Brakke, Kenneth A.; Dostie, Ashley M.; Theberge, Ashleigh B.; Berthier, Erwin (2018-04-25). "Droplet Behavior in Open Biphasic Microfluidics". Langmuir. 34 (18): 5358–5366. doi:10.1021/acs.langmuir.8b00380. ISSN 0743-7463.
  26. 1 2 Zhao, B. (2001-02-09). "Surface-Directed Liquid Flow Inside Microchannels". Science. 291 (5506): 1023–1026. doi:10.1126/science.291.5506.1023. ISSN 0036-8075.
  27. ↑ Young, Edmond W.K.; Berthier, Erwin; Beebe, David J. (2013-01-02). "Assessment of enhanced autofluorescence and impact on cell microscopy for microfabricated thermoplastic devices". Analytical Chemistry. 85 (1): 44–49. doi:10.1021/ac3034773. ISSN 0003-2700. PMC 4017339. PMID 23249264.
  28. ↑ Sackmann, Eric K.; Fulton, Anna L.; Beebe, David J. (2014-03-12). "The present and future role of microfluidics in biomedical research". Nature. 507 (7491): 181–189. doi:10.1038/nature13118. ISSN 0028-0836.
  29. ↑ Brakke, Kenneth A. (2015-01-31). The Motion of a Surface by Its Mean Curvature. (MN-20). Princeton: Princeton University Press. ISBN 9781400867431.
  30. 1 2 Kachel, Sibylle; Zhou, Ying; Scharfer, Philip; Vrančić, Christian; Petrich, Wolfgang; Schabel, Wilhelm (2014). "Evaporation from open microchannel grooves". Lab Chip. 14 (4): 771–778. doi:10.1039/c3lc50892g. ISSN 1473-0197.
  31. 1 2 Higashi, Kazuhiko; Ogawa, Miho; Fujimoto, Kazuma; Onoe, Hiroaki; Miki, Norihisa (2017-06-03). "Hollow Hydrogel Microfiber Encapsulating Microorganisms for Mass-Cultivation in Open Systems". Micromachines. 8 (6): 176. doi:10.3390/mi8060176. ISSN 2072-666X.
  32. ↑ Dak, Piyush; Ebrahimi, Aida; Swaminathan, Vikhram; Duarte-Guevara, Carlos; Bashir, Rashid; Alam, Muhammad (2016-04-14). "Droplet-based Biosensing for Lab-on-a-Chip, Open Microfluidics Platforms". Biosensors. 6 (2): 14. doi:10.3390/bios6020014. ISSN 2079-6374.
  33. ↑ Hsu, Chia-Hsien; Chen, Chihchen; Folch, Albert (2004). ""Microcanals" for micropipette access to single cells in microfluidic environments". Lab Chip. 4 (5): 420–424. doi:10.1039/b404956j. ISSN 1473-0197.
  34. ↑ Li, C.; Boban, M.; Tuteja, A. (2017). "Open-channel, water-in-oil emulsification in paper-based microfluidic devices". Lab on a Chip. 17 (8): 1436–1441. doi:10.1039/c7lc00114b. ISSN 1473-0197.
  35. ↑ Gutzweiler, Ludwig; Gleichmann, Tobias; Tanguy, Laurent; Koltay, Peter; Zengerle, Roland; Riegger, Lutz (2017-05-15). "Open microfluidic gel electrophoresis: Rapid and low cost separation and analysis of DNA at the nanoliter scale". Electrophoresis. 38 (13–14): 1764–1770. doi:10.1002/elps.201700001. ISSN 0173-0835.
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