Microfluidics

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The microfluidics deals with the behavior of liquids and gases in the smallest space. This can differ significantly from the behavior of macroscopic fluids , because in this order of magnitude effects can dominate that are often neglected in classical fluid mechanics .

technology

Microfluidic devices made of silicone and glass.
Above: Picture of the parts
Below: Photo and microscopic image of a channel 15 µm wide

Smallest quantities of fluids are moved, mixed, separated or otherwise processed.

particularities

  • Frictional forces dominate the inertial forces. This corresponds to a flow with small Reynolds numbers , a laminar flow is created without significant turbulence . This makes the mixing of liquids more difficult, which is only possible through diffusion without turbulence .
  • The possible dominance of capillary forces over weight . This is expressed in a small bond number and means that when transporting very small amounts of liquid, contrary to everyday experience, gravity can be neglected.

Passive movement

Passive movement can be generated, for example, via capillary fluid structures. In addition, external drive mechanisms such as. B. rotating systems are used, through which the use of centrifugal force is possible to drive the liquid transport. In this way, targeted guidance of the media transport can be achieved in purely passive fluidic systems.

Active movement

We speak of “active microfluidics” when the manipulation of the working fluids is specifically controlled by active (micro) components such as micropumps or microvalves . Micropumps convey or dose liquids, microvalves determine the direction or the mode of movement of the pumped media. Micromixers enable the targeted mixing of fluid volumes.

construction

Depending on the application / requirement, different technologies and material groups are used, such as glass (also photo-structurable glass such as Foturan ), plastic or silicon . Thanks to the advanced technology, it is now possible to automatically manufacture microfluidic products very inexpensively and to ensure their quality.

Prototyping

For the production of prototypes, poly-dimethyl-siloxane ( PDMS ) is often bonded to glass (see Rapid Prototyping ), or two individual PDMS half-parts are bonded together after the surfaces have been activated or radicalized with reactive oxygen plasma. A new method also allows PDMS-PDMS hybrids to be made that have clear side surfaces and thus enable multi-angle imaging. The rapid production of prototypes for microfluidics with a special epoxy resin (SU-8) is now also possible with a 3D printer . The precision of the process is demonstrated with a sample, a 24-nozzle printhead with 100 µm nozzles. In general, it has been assumed since 2016 that the complex construction of microfluidic elements made of PDMS, which involves a lot of manual work, will be completely replaced by products from the 3D printer.

application areas

Applications can be found in many areas of biology, medicine and technology, often under the label chip laboratory . The best known application of microfluidics today is the print head for inkjet printers.

Cell cultures

In microfluidic components, individual cells, but also complete tissues or parts of organs, are cultivated and analyzed.

Drug research

Microfluidics is used successfully in research into new drugs.

Rapid tests

There are technical applications in biotechnology, medical technology (especially for point-of-care diagnostics )

Other uses

Further technical applications can be found in process technology, sensor technology and, more recently, in the examination of consumer goods in the food industry.

Form of application

Often, processes which are otherwise carried out in a lab can, to increase efficiency and mobility or for reducing the substances required on a single chip, called the Chip laboratory be performed.

Drop-based microfluidics

If two immiscible liquids are specifically sent through a microchannel, phase boundaries are formed and one liquid forms drops within the other. This is known as drop-based microfluidics or digital microfluidics. The drop-based microfluidics is a (partially) serial alternative to microtiter plates . Usually, entire sequences of drops are generated. These drops represent experimental vessels in which chemical reactions and biological processes are examined. They can also be used for logical information processing.

Microfluid segment technology

The microfluidic technology segment is a special case of the drop-based microfluidics. She will u. a. used for particle synthesis, for combinatorial synthesis experiments, in flow thermocyclers for the polymerase chain reaction (PCR), in micro flow calorimetry , for the search for unknown microorganisms and in microtoxicology .

See also

Web links

Individual evidence

  1. ↑ Matilda Jordanova-Duda: A strong memory: shape memory alloy (SMA) as a mini actuator. VDI-Nachrichten, May 2, 2019, archived from the original on May 3, 2019 ; accessed on January 12, 2020 .
  2. ↑ Gerhard Vogel: Mini-Valves: Special solution for the smallest medical products. Medicine & Technology, February 12, 2018, accessed June 11, 2019 .
  3. ↑ Ryan Pawell, David W. Inglis, Tracie J. Barber: Manufacturing and wetting low-cost microfluidic cell separation devices . In: Biomicrofluidics . 5th edition. No. 7 , 2013, p. 056501 , doi : 10.1063 / 1.4821315 (English, researchgate.net ).
  4. ↑ Ryan Pawell, Robert A. Taylor, Kevin V. Morris et al .: Automating microfluidic part verification . In: Microfluidics and Nanofluidics . 4th edition. No. 18 , 2015, p. 657–665 , doi : 10.1007 / s10404-014-1464-1 (English).
  5. ↑ Axel Hochstetter: Presegmentation Procedure Generates Smooth-Sided Microfluidic Devices: Unlocking Multiangle Imaging for Everyone? In: ACS Omega . December 2, 2019, ISSN  2470-1343 , p. 20972–20977 , doi : 10.1021 / acsomega.9b02139 (English, acs.org [PDF; 3.9 MB ; accessed on December 11, 2019]).
  6. ^ Benjamin Bohl, Reinhard Steger, Roland Zengerle, Peter Koltay: Multi-layer SU-8 lift-off technology for microfluidic devices . In: Journal of Micromechanics and Microengineering . 15th edition. No. 6 , April 2005, doi : 10.1088 / 0960-1317 / 15/6/002 (English, iop.org ).
  7. ^ Anthony K. Au, Wilson Huynh, Lisa F. Horowitz, Albert Folch: 3D-Printed Microfluidics. (PDF; 15.148kByte) February 2016, accessed on February 10, 2020 (English).
  8. ↑ Andrew J. deMello: Control and detection of chemical reactions in microfluidic systems . In: Nature . No. 442 , July 2006, p. 394–402 , doi : 10.1038 / nature05062 (English).
  9. ↑ C. Regnault, DS Dheeman, A. Hochstetter: Microfluidic Devices for Drug assays . In: High-Throughput . 2nd Edition. No. 2 , June 20, 2018, doi : 10.3390 / ht7020018 (English, mdpi.com [accessed January 12, 2020]).
  10. ↑ Eric W. Esch, Anthony Bahinski, Dongeun Huh: Organs-on-chips at the frontiers of drug discovery. In: nature reviews, drug discovery. March 20, 2015, accessed February 10, 2020 .
  11. ↑ Michael P. Barrett, Jonathan M. Cooper et al .: Microfluidics-Based Approaches to the Isolation of African Trypanosomes . In: Pathogens . 4th edition. No. 6 , October 5, 2017, doi : 10.3390 / pathogens6040047 (English, mdpi.com [accessed January 12, 2020]).
  12. ↑ Karin Martin, Thomas Henkel et al .: Generation of larger numbers of separated microbial populations by cultivation in segmented-flow microdevices . In: Lab on a Chip . No. 3 , June 3, 2003, p. 202–203 , doi : 10.1039 / b301258c (English, rsc.org [accessed January 12, 2020]).
  13. ↑ Manu Prakash, Neil Gershenfeld et al .: Microfluid Bubble Logic . In: Science . 5813th edition. No. 315 , February 9, 2007, p. 832–835 , doi : 10.1126 / science.1136907 (English, sciencemag.org [accessed January 12, 2020]).
  14. ↑ Michael J. Köhler, Brian P. Cahill: Micro-Segmented Flow . Ed .: Springer. Berlin-Heidelberg 2014, ISBN 978-3-642-38779-1 (English).