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A Ti-Cr-Pt tube (~40 μm long) releases oxygen bubbles when immersed in hydrogen peroxide (catalytic decomposition). Polystyrene spheres (1 μm diameter) were added to study the flow kinetics.[1]
Electrochemical micropump activating the flow of human blood through a 50×100 μm pipe.[2]

Micropumps are devices that can control and manipulate small fluid volumes.[3] Although any kind of small pump is often referred to as micropump, a more accurate definition restricts this term to pumps with functional dimensions in the micrometer range. Such pumps are of special interest in microfluidic research, and have become available for industrial product integration in recent years. Their miniaturized overall size, potential cost and improved dosing accuracy compared to existing miniature pumps fuel the growing interest for this innovative kind of pump.

Note that the below text is very incomplete in terms of providing a good overview of the different micropump types and applications, and therefore please refer to good review articles on the topic.[4][5][6][7]

Contents

Introduction and HistoryEdit

First true micropumps were reported in the mid-1970s,[8] but attracted interest only in the 1980s, when Jan Smits and Harald Van Lintel developed MEMS micropumps.[9] Most of the fundamental MEMS micropump work was done in the 1990s. More recently, efforts have been made to design non-mechanical micropumps that are functional in remote locations due to their non-dependence on external power.

 
A diagram showing how three microvalves in series can be used to displace fluid. In step (A), fluid is pulled from the inlet into the first valve. Steps (B) - (E) move the fluid to the final valve, before the fluid is expelled towards the outlet in step (F).

Types and TechnologyEdit

Within the microfluidic world, physical laws change their appearance.[10] As an example, volumetric forces, such as weight or inertia, often become negligible, whereas surface forces can dominate fluidical behaviour, especially when gas inclusion in liquids is present. With only a few exceptions, micropumps rely on micro-actuation principles, which can reasonably be scaled up only to a certain size.

Micropumps can be grouped into mechanical and non-mechanical devices.[11] Mechanical systems contain moving parts, which are usually actuation and microvalve membranes or flaps. The driving force can be generated by utilizing piezoelectric, electrostatic, thermo-pneumatic, pneumatic or magnetic effects. Non-mechanical pumps function with electro-hydrodynamic, electro-osmotic, electrochemical [12] or ultrasonic flow generation, just to name a few of the actuation mechanisms that are currently studied.

Mechanical MicropumpsEdit

Diaphragm MicropumpsEdit

A diaphragm micropump uses the repeated actuation of a diaphragm to drive a fluid. The membrane is positioned above a main pump valve, which is centered between inlet and outlet microvalves. When the membrane is deflected upwards through some driving force, fluid is pulled into the inlet valve into the main pump valve. The membrane is then lowered, expelling the fluid through the outlet valve. This process is repeated to pump fluid continuously.[6]

Peristaltic MicropumpsEdit

A peristaltic micropump is a micropump composed of at least three microvalves in series. These three valves are opened and closed sequentially in order to pull fluid from the inlet to the outlet in a process known as peristalsis.[13]

Non-Mechanical MicropumpsEdit

Valveless MicropumpsEdit

Static valves are defined as valves which have fixed geometry without any moving parts. These valves provide flow rectification through addition of energy (active) or inducing desired flow behavior by fluid inertia (passive). Two most common types of static geometry passive valves are Diffuser-Nozzle Elements [14][15] and Tesla valves. Micropumps having nozzle-diffuser elements as flow rectification device are commonly known as Valveless Micropumps.

Capillary PumpsEdit

In microfluidics, capillary pumping plays an important role because the pumping action does not require external actuation power. Glass capillaries and porous media, including nitrocellulose paper and synthetic paper,[16] can be integrated into microfluidic chips. Capillary pumping is widely used in lateral flow testing. Recently, novel capillary pumps, with a constant pumping flow rate independent of the liquid viscosity and surface energy,[17][18][19][20] were developed, which have a significant advantage over the traditional capillary pump (of which the flow behaviour is Washburn behaviour, namely the flow rate is not constant) because their performance does not depend on the sample viscosity.

Chemically Powered PumpsEdit

Chemically powered non-mechanical pumps have been fabricated by affixing nanomotors to surfaces, driving fluid flow through chemical reactions. A wide variety of pumping systems exist including biological enzyme based pumps,[21][22][23][24][25] organic photocatalyst pumps,[26] and metal catalyst pumps.[24][27] These pumps generate flow through a number of different mechanisms including self-diffusiophoresis, electrophoresis, bubble propulsion and the generation of density gradients.[22][25][28] Moreover, these chemically powered micropumps can be used as sensors for the detection of toxic agents.[23]

ApplicationsEdit

Micropumps have potential industrial applications, such as delivery of small amounts of glue during manufacturing processes, and biomedical applications, including portable or implanted drug delivery devices. Bio-inspired applications include a flexible electromagnetic micropump using magnetorheological elastomer to replace lymphatic vessels.[29] Chemically powered micropumps also demonstrate potential for applications in chemical sensing in terms of detecting chemical warfare agents and environmental hazards, such as mercury and cyanide.[23]

See alsoEdit

ReferencesEdit

  1. ^ Solovev, Alexander A.; Sanchez, Samuel; Mei, Yongfeng; Schmidt, Oliver G. (2011). "Tunable catalytic tubular micro-pumps operating at low concentrations of hydrogen peroxide". Physical Chemistry Chemical Physics. 13 (21): 10131–5. Bibcode:2011PCCP...1310131S. doi:10.1039/C1CP20542K. PMID 21505711.
  2. ^ Chiu, S. H.; Liu, C. H. (2009). "An air-bubble-actuated micropump for on-chip blood transportation". Lab on a Chip. 9 (11): 1524–33. doi:10.1039/B900139E. PMID 19458858.
  3. ^ Laser, D. J.; Santiago, J. G. (2004). "A review of micropumps". Journal of Micromechanics and Microengineering. 14 (6): R35. Bibcode:2004JMiMi..14R..35L. doi:10.1088/0960-1317/14/6/R01. ISSN 0960-1317.
  4. ^ Laser and Santiago (2004). "A review of micropumps". J. Micromech. Microeng. 14 (6): R35–R64. Bibcode:2004JMiMi..14R..35L. doi:10.1088/0960-1317/14/6/R01.
  5. ^ Nguyen; et al. (2002). "MEMS-Micropumps: A Review". J. Fluids Eng. 124 (2): 384. doi:10.1115/1.1459075.
  6. ^ a b Iverson; et al. (2008). "Recent advances in microscale pumping technologies: a review and evaluation". Microfluid Nanofluid. 5 (2): 145–174. doi:10.1007/s10404-008-0266-8.
  7. ^ Amirouche; et al. (2009). "Current micropump technologies and their biomedical applications". Microsystem Technologies. 15 (5): 647–666. doi:10.1007/s00542-009-0804-7.
  8. ^ Thomas, L.J. and Bessman, S.P. (1975) "Micropump powered by piezoelectric disk benders", U.S. Patent 3,963,380
  9. ^ Woias, P (2005). "Micropumps – past progress and future prospects". Sensors and Actuators B. 105 (1): 28–38. doi:10.1016/j.snb.2004.02.033.
  10. ^ Order from Chaos Archived 2008-07-23 at the Wayback Machine, The CAFE Foundation
  11. ^ Abhari, Farideh; Jaafar, Haslina & Yunus, Nurul Amziah Md (2012). "A Comprehensive Study of Micropumps Technologies" (PDF). International Journal of Electrochemical Science. 7 (10): 9765–9780.
  12. ^ Neagu, C.R.; Gardeniers, J.G.E.; Elwenspoek, M.; Kelly, J.J. (1996). "An electrochemical microactuator: principle and first results". Journal of Microelectromechanical Systems. 5 (1): 2–9. doi:10.1109/84.485209.
  13. ^ Smits, Jan G. (1990). "Piezoelectric micropump with three valves working peristaltically". Sensors and Actuators A: Physical. 21 (1–3): 203–206. doi:10.1016/0924-4247(90)85039-7.
  14. ^ Stemme and Stemme (1993). "A valveless diffuser/nozzle-based fluid pump". Sensors and Actuators A: Physical. 39 (2): 159–167. doi:10.1016/0924-4247(93)80213-Z.
  15. ^ van der Wijngaart (2001). "A valve-less diffuser micropump for microfluidic analytical systems". Sensors and Actuators B: Chemical. 72 (3): 259–265. doi:10.1016/S0925-4005(00)00644-4.
  16. ^ Jonas Hansson; Hiroki Yasuga; Tommy Haraldsson; Wouter van der Wijngaart (2016). "Synthetic microfluidic paper: high surface area and high porosity polymer micropillar arrays". Lab on a Chip. 16 (2): 298–304. doi:10.1039/C5LC01318F. PMID 26646057.
  17. ^ Weijin Guo; Jonas Hansson; Wouter van der Wijngaart (2016). "Viscosity Independent Paper Microfluidic Imbibition" (PDF). MicroTAS 2016, Dublin, Ireland.
  18. ^ Weijin Guo; Jonas Hansson; Wouter van der Wijngaart (2016). "Capillary Pumping Independent of Liquid Sample Viscosity". Langmuir. 32 (48): 12650–12655. doi:10.1021/acs.langmuir.6b03488. PMID 27798835.
  19. ^ Weijin Guo; Jonas Hansson; Wouter van der Wijngaart (2017). Capillary pumping with a constant flow rate independent of the liquid sample viscosity and surface energy. IEEE MEMS 2017, las Vegas, USA. pp. 339–341. doi:10.1109/MEMSYS.2017.7863410. ISBN 978-1-5090-5078-9.
  20. ^ Weijin Guo; Jonas Hansson; Wouter van der Wijngaart (2018). "Capillary pumping independent of the liquid surface energy and viscosity". Microsystems & Nanoengineering, 2018, 4(1): 2. 4 (1): 2. Bibcode:2018MicNa...4....2G. doi:10.1038/s41378-018-0002-9. PMID 31057892.
  21. ^ Sengupta, S.; Patra, D.; Ortiz-Rivera, I.; Agrawal, A.; Shklyaev, S.; Dey, K. K.; Córdova-Figueroa, U.; Mallouk, T. E.; Sen, A. (2014). "Self-powered enzyme micropumps". Nature Chemistry. 6 (5): 415–422. Bibcode:2014NatCh...6..415S. doi:10.1038/nchem.1895. PMID 24755593.
  22. ^ a b Ortiz-Rivera, I.; Shum, H.; Agrawal, A.; Balazs, A. C.; Sen, A. (2016). "Convective flow reversal in self-powered enzyme micropumps". Proceedings of the National Academy of Sciences. 113 (10): 2585–2590. Bibcode:2016PNAS..113.2585O. doi:10.1073/pnas.1517908113. PMC 4791027. PMID 26903618.
  23. ^ a b c Ortiz-Rivera, I.; Courtney, T.; Sen, A. (2016). "Enzyme Micropump-Based Inhibitor Assays". Advanced Functional Materials. 26 (13): 2135–2142. doi:10.1002/adfm.201504619.
  24. ^ a b Das, S.; Shklyaev, O. E.; Altemose, A.; Shum, H.; Ortiz-Rivera, I.; Valdez, L.; Mallouk, T. E.; Balazs, A. C.; Sen, A. (2017-02-17). "Harnessing catalytic pumps for directional delivery of microparticles in microchambers". Nature Communications. 8: 14384. Bibcode:2017NatCo...814384D. doi:10.1038/ncomms14384. ISSN 2041-1723. PMC 5321755. PMID 28211454.
  25. ^ a b Valdez, L.; Shum, H.; Ortiz-Rivera, I.; Balazs, A. C.; Sen, A. (2017). "Solutal and thermal buoyancy effects in self-powered phosphatase micropumps". Soft Matter. 13 (15): 2800–2807. Bibcode:2017SMat...13.2800V. doi:10.1039/C7SM00022G. PMID 28345091.
  26. ^ Yadav, V.; Zhang, H.; Pavlick, R.; Sen, A. (2012). "Triggered "On/Off" Micropumps and Colloidal Photodiode". Journal of the American Chemical Society. 134 (38): 15688–15691. doi:10.1021/ja307270d. PMID 22971044.
  27. ^ Solovev, A. A.; Sanchez, S.; Mei, Y.; Schmidt, O. G. (2011). "Tunable catalytic tubular micro-pumps operating at low concentrations of hydrogen peroxide". Physical Chemistry Chemical Physics. 13 (21): 10131–10135. Bibcode:2011PCCP...1310131S. doi:10.1039/c1cp20542k. PMID 21505711.
  28. ^ Yadav, V.; Duan, W.; Butler, P. J.; Sen, A. (2015). "Anatomy of Nanoscale Propulsion". Annual Review of Biophysics. 44 (1): 77–100. doi:10.1146/annurev-biophys-060414-034216. PMID 26098511.
  29. ^ Behrooz, M. & Gordaninejad, F. (2014). "A flexible magnetically-controllable fluid transport system". Active and Passive Smart Structures and Integrated Systems 2014. Active and Passive Smart Structures and Integrated Systems 2014. 9057. pp. 90572Q. doi:10.1117/12.2046359.