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arxiv: 2407.09960 · v2 · submitted 2024-07-13 · ❄️ cond-mat.soft

Active nematic pumps

Ignasi V\'elez-Ceron , Rodrigo C.V. Coelho , Pau Guillamat , Marc Verg\'es-Vilarrubia , Margarida Telo da Gama , Francesc Sagu\'es , Jordi Ign\'es-Mullol This is my paper

Pith reviewed 2026-05-23 22:59 UTC · model grok-4.3

classification ❄️ cond-mat.soft
keywords active nematicself-pumpingmicrofluidicsactive turbulencetriangular inclusionscargo transportmixingsymmetry breaking
0
0 comments X

The pith

Triangular inclusions in active nematic gels break fore-aft symmetry to stabilize self-pumping flows.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The paper shows that embedding triangular objects in an active nematic gel disrupts the usual chaotic flows of active turbulence, producing a consistent net directed flow without external power or walls. This matters for microfluidics because it turns an inherently messy active material into a source of reliable pumping that can move cargo and mix fluids on its own. Experiments and simulations confirm the triangles create usable output velocity and pressure, both alone and in groups, and allow the flow geometry to be shaped by placement. The result is a route to autonomous microscale fluid handling powered only by the material's internal activity.

Core claim

The addition of triangular-shaped inclusions into an active nematic gel can locally break the fore-aft symmetry of active turbulence and stabilize flow fields with self-pumping capabilities, enabling wall-free and self-powered microfluidic systems for cargo transport and mixing along the downstream flow, with performance quantified by output velocity and hydrostatic pressure in both isolated and ensemble configurations.

What carries the argument

Triangular-shaped inclusions that break fore-aft symmetry of active turbulence to produce directed pumping.

If this is right

  • The system generates usable output velocity and hydrostatic pressure buildup for transport tasks.
  • Mixing occurs naturally along the stabilized downstream flow.
  • Cooperative placement of multiple inclusions increases overall pumping performance.
  • The approach allows tailoring of flow geometry inside specifically designed microfluidic platforms.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

  • Arrays of these pumps could enable complex autonomous flow networks without external valves or controls.
  • The same symmetry-breaking principle might apply to other active systems, such as bacterial suspensions, to produce directed transport.
  • If the directed flow persists at larger scales, these pumps could support macroscopic devices that harvest activity for fluid handling.

Load-bearing premise

The net directed flow created by each triangle will remain stable and additive rather than being erased by the surrounding chaotic turbulence when inclusions are used in groups or at larger scales.

What would settle it

Measuring zero net average flow velocity across an array of triangular inclusions in an active nematic, with flows fluctuating symmetrically in both directions.

Figures

Figures reproduced from arXiv: 2407.09960 by Francesc Sagu\'es, Ignasi V\'elez-Ceron, Jordi Ign\'es-Mullol, Marc Verg\'es-Vilarrubia, Margarida Telo da Gama, Pau Guillamat, Rodrigo C.V. Coelho.

Figure 1
Figure 1. Figure 1: FIG. 1 [PITH_FULL_IMAGE:figures/full_fig_p003_1.png] view at source ↗
Figure 2
Figure 2. Figure 2: FIG. 2 [PITH_FULL_IMAGE:figures/full_fig_p004_2.png] view at source ↗
Figure 3
Figure 3. Figure 3: FIG. 3 [PITH_FULL_IMAGE:figures/full_fig_p005_3.png] view at source ↗
Figure 4
Figure 4. Figure 4: FIG. 4 [PITH_FULL_IMAGE:figures/full_fig_p006_4.png] view at source ↗
Figure 5
Figure 5. Figure 5: FIG. 5 [PITH_FULL_IMAGE:figures/full_fig_p007_5.png] view at source ↗
read the original abstract

Microfluidics involves the manipulation of flows at the microscale, typically requiring external power sources to generate pressure gradients. Alternatively, harnessing flows from active fluids, which are usually chaotic, has been proposed as a paradigm for the development of micro-machines. Here, by combining experimental realizations and simulations, we demonstrate that the addition of triangular-shaped inclusions into an active nematic gel can locally break the fore-aft symmetry of active turbulence and stabilize flow fields with self-pumping capabilities. The proposed strategy has enabled us to generate wall-free and self-powered microfluidic systems capable of both cargo transport and mixing along with the downstream flow. We analyze the performance of these active pumps, both isolated and within cooperative ensembles in terms of their output velocity and hydrostatic pressure buildup. Finally, we demonstrate strategies to incorporate them into specifically designed microfluidic platforms to advantageously tailor the geometry of active flows. Our results reveal new possibilities for leveraging the self-organized mechanodynamics of active fluids.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Referee Report

1 major / 2 minor

Summary. The paper claims that adding triangular-shaped inclusions to an active nematic gel locally breaks the fore-aft symmetry of active turbulence, stabilizing directed self-pumping flows. This is shown via combined experiments and simulations to create wall-free, self-powered microfluidic systems for cargo transport and mixing. Performance of isolated pumps and cooperative ensembles is analyzed via output velocity and hydrostatic pressure buildup, with demonstrations of integration into designed microfluidic platforms.

Significance. If substantiated, the result would be significant for active matter and microfluidics by providing a geometry-based route to convert chaotic active flows into controllable directed pumping without external power. The experimental-simulation combination is a strength for exploring the symmetry-breaking mechanism and its scalability.

major comments (1)
  1. [cooperative ensembles analysis] The section analyzing cooperative ensembles: the claim that net directed flow remains stable in arrays requires explicit quantitative checks (e.g., time-averaged velocity fields or pressure vs. number of inclusions) to rule out cancellation by re-emergent active turbulence, as this is load-bearing for the scalability assertion.
minor comments (2)
  1. [Abstract] The abstract states the central result but contains no numerical values, error bars, or sample sizes; move at least one key metric (e.g., typical pumping velocity) into the abstract for immediate assessment.
  2. Ensure all simulation and experimental figures include scale bars, flow-direction arrows, and statistical measures of variability.

Simulated Author's Rebuttal

1 responses · 0 unresolved

We thank the referee for their positive assessment of the work and for the recommendation of minor revision. We address the single major comment below.

read point-by-point responses

  1. Referee: The section analyzing cooperative ensembles: the claim that net directed flow remains stable in arrays requires explicit quantitative checks (e.g., time-averaged velocity fields or pressure vs. number of inclusions) to rule out cancellation by re-emergent active turbulence, as this is load-bearing for the scalability assertion.

    Authors: We agree that additional explicit quantitative checks would strengthen the scalability claim. The current manuscript reports output velocity and hydrostatic pressure for cooperative ensembles, but does not include the requested time-averaged velocity fields across array sizes or pressure versus number of inclusions. In the revised manuscript we will incorporate these analyses from existing and supplementary simulation data to demonstrate that net directed flow persists without cancellation by re-emergent turbulence. revision: yes

Circularity Check

0 steps flagged

No significant circularity

full rationale

The work is experimental and simulation-based with no derivation chain, equations, or fitted parameters that reduce the pumping result to inputs by construction. Central claims rest on direct observation of symmetry breaking by triangular inclusions and verifiable flow outcomes, independent of self-citation loops or ansatzes. No load-bearing self-citations or self-definitional steps are present.

Axiom & Free-Parameter Ledger

0 free parameters · 0 axioms · 0 invented entities

No mathematical derivations or free parameters are described in the abstract; the work relies on standard assumptions of active nematic hydrodynamics.

pith-pipeline@v0.9.0 · 5722 in / 927 out tokens · 13365 ms · 2026-05-23T22:59:07.438133+00:00 · methodology

discussion (0)

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Forward citations

Cited by 2 Pith papers

Reviewed papers in the Pith corpus that reference this work. Sorted by Pith novelty score.

  1. Spontaneous rotation and propulsion of suspended capsules in active nematics

    cond-mat.soft 2025-10 unverdicted novelty 6.0

    Elastic capsules in active nematics exhibit geometry-dependent spontaneous rotation and propulsion that is suppressed by capsule deformability.

  2. Solute dispersion in pre-turbulent confined active nematics

    cond-mat.soft 2024-10 unverdicted novelty 5.0

    Simulations show longitudinal solute dispersion in pre-turbulent confined active nematics is set by second moments of velocity components, scales with activity, and reaches up to 10x molecular diffusion in dancing flows.

Reference graph

Works this paper leans on

57 extracted references · 57 canonical work pages · cited by 2 Pith papers · 1 internal anchor

  1. [1]

    Active gel preparation Microtubules (MTs) were polymerized from het- erodimeric ( α,β)-tubulin from bovine brain (Brandeis University Biological Materials Facility). Tubulin (8 mg mL -1) was incubated at 37 °C for 30 min in aque- ous M2B buffer (80 mM Pipes (piperazine-N,N’-bis(2- ethanesulfonic acid)), 1 mM EGTA (ethylene glycol- bis(β-aminoethyl ether)-...

    work page

  2. [2]

    GMPCPP is a non-hydrolysable guanosine triphosphate (GTP) analogue that favours the forma- tion of stable MTs, obtaining high-density suspensions of short MTs (1-2 µm)

    up to a concentration of 1 mM and 0.6 mM, re- spectively. GMPCPP is a non-hydrolysable guanosine triphosphate (GTP) analogue that favours the forma- tion of stable MTs, obtaining high-density suspensions of short MTs (1-2 µm). 3% of the total tubulin concen- tration was labelled with Alexa 647 to allow their obser- vation by means of fluorescence microsco...

    work page

  3. [3]

    A 50 µm height double-sided tape was used as a spacer, leaving a channel of ∼4 mm width

    Active nematic cell Flow cells were prepared with a bioinert and superhy- drophilic polyacrylamide-coated glass and a hydrophobic aquapel-coated glass. A 50 µm height double-sided tape was used as a spacer, leaving a channel of ∼4 mm width. 10 The cell was filled first with fluorinated oil (HFE7500; Fluorochem; 051243) which contains a 2% of a fluoro- sur...

    work page

  4. [4]

    We used a Nikon Eclipse Ti2-e equipped with a white LED source (Thor- labs MWWHLP1), a Cy5 filter cube (Edmund Optics) and a FITR filter cube (Thorlabs, TLV-TE2000-FITC)

    Imaging and photopatterning The observation of the active material was done by means of fluorescence microscopy. We used a Nikon Eclipse Ti2-e equipped with a white LED source (Thor- labs MWWHLP1), a Cy5 filter cube (Edmund Optics) and a FITR filter cube (Thorlabs, TLV-TE2000-FITC). Images were captured using an Andor Zyla 4.2 Plus cam- era or a QImaging ...

    work page

  5. [5]

    Flow field analysis and particle tracking The flow field of the active material was extracted by performing particle image velocimetry directly on the flu- orescence images using the public domain MatLab App PIVLab. To study the transport of advected colloidal particles, we have included a small amount of 1 µm hy- drophilic fluorescent polystyrene micropa...

    work page

  6. [6]

    Battat, D

    S. Battat, D. A. Weitz, and G. M. Whitesides, An out- look on microfluidics: the promise and the challenge, Lab Chip 22, 530 (2022)

    work page 2022

  7. [7]

    Di Leonardo, L

    R. Di Leonardo, L. Angelani, D. Dell’arciprete, G. Ruocco, V. Iebba, S. Schippa, M. P. Conte, F. Mecarini, F. De Angelis, and E. Di Fabrizio, Bacterial ratchet motors, Proc. Natl. Acad. Sci. U S A 107, 9541 (2010)

    work page 2010

  8. [8]

    S. P. Thampi, A. Doostmohammadi, T. N. Shendruk, R. Golestanian, and J. M. Yeomans, Active microma- chines: Microfluidics powered by mesoscale turbulence, Sci Adv 2, e1501854 (2016)

    work page 2016

  9. [9]

    S. Ray, J. Zhang, and Z. Dogic, Rectified rotational dy- namics of mobile inclusions in two-dimensional active ne- matics, Physical Review Letters 130 (2023)

    work page 2023

  10. [10]

    Bricard, J

    A. Bricard, J. B. Caussin, N. Desreumaux, O. Dauchot, and D. Bartolo, Emergence of macroscopic directed mo- tion in populations of motile colloids, Nature 503, 95 (2013)

    work page 2013

  11. [11]

    Dombrowski, L

    C. Dombrowski, L. Cisneros, S. Chatkaew, R. E. Gold- stein, and J. O. Kessler, Self-concentration and large- scale coherence in bacterial dynamics, Phys Rev Lett 93, 098103 (2004)

    work page 2004

  12. [12]

    H. H. Wensink, J. Dunkel, S. Heidenreich, K. Drescher, R. E. Goldstein, H. Lowen, and J. M. Yeomans, Meso- scale turbulence in living fluids, Proc Natl Acad Sci U S A 109, 14308 (2012)

    work page 2012

  13. [13]

    S. Zhou, A. Sokolov, O. D. Lavrentovich, and I. S. Aran- son, Living liquid crystals, Proc Natl Acad Sci U S A 111, 1265 (2014)

    work page 2014

  14. [14]

    Lu and V

    W. Lu and V. I. Gelfand, Go with the flow - bulk trans- port by molecular motors, J Cell Sci 136 (2023)

    work page 2023

  15. [15]

    D. A. Fletcher and R. D. Mullins, Cell mechanics and the cytoskeleton, Nature 463, 485 (2010). 12

    work page 2010

  16. [16]

    Sanchez, D

    T. Sanchez, D. T. Chen, S. J. DeCamp, M. Heymann, and Z. Dogic, Spontaneous motion in hierarchically as- sembled active matter, Nature 491, 431 (2012)

    work page 2012

  17. [17]

    M. P. Murrell and M. L. Gardel, F-actin buckling coor- dinates contractility and severing in a biomimetic acto- myosin cortex, Proc Natl Acad Sci U S A 109, 20820 (2012)

    work page 2012

  18. [18]

    Ramaswamy, The mechanics and statistics of active matter, Annual Review of Condensed Matter Physics 1, 323 (2010)

    S. Ramaswamy, The mechanics and statistics of active matter, Annual Review of Condensed Matter Physics 1, 323 (2010)

    work page 2010

  19. [19]

    M. C. Marchetti, J. F. Joanny, S. Ramaswamy, T. B. Liverpool, J. Prost, M. Rao, and R. A. Simha, Hydrody- namics of soft active matter, Reviews of Modern Physics 85, 1143 (2013)

    work page 2013

  20. [20]

    Needleman and Z

    D. Needleman and Z. Dogic, Active matter at the inter- face between materials science and cell biology, Nature Reviews Materials 2, 1 (2017)

    work page 2017

  21. [21]

    Sagu´ es,Colloidal Active Matter (Taylor and Francis Group, Boca Raton, FL, 2023)

    F. Sagu´ es,Colloidal Active Matter (Taylor and Francis Group, Boca Raton, FL, 2023)

    work page 2023

  22. [22]

    K. T. Wu, J. B. Hishamunda, D. T. Chen, S. J. De- Camp, Y. W. Chang, A. Fernandez-Nieves, S. Fraden, and Z. Dogic, Transition from turbulent to coherent flows in confined three-dimensional active fluids, Science 355, eaal1979 (2017)

    work page 2017

  23. [23]

    Shankar, L

    S. Shankar, L. V. D. Sharrer, M. J. Bowick, and M. C. Marchetti, Design rules for controlling active topological defects, Proc. Natl. Acad. Sci. U S A 121, e2400933121 (2024)

    work page 2024

  24. [24]

    Prost, F

    J. Prost, F. Julicher, and J. F. Joanny, Active gel physics, Nature Physics 11, 111 (2015)

    work page 2015

  25. [25]

    Doostmohammadi, J

    A. Doostmohammadi, J. Ign´ es-Mullol, J. M. Yeomans, and F. Sagu´ es, Active nematics, Nature communications 9, 3246 (2018)

    work page 2018

  26. [26]

    Opathalage, M

    A. Opathalage, M. M. Norton, M. P. Juniper, B. Langes- lay, S. A. Aghvami, S. Fraden, and Z. Dogic, Self- organized dynamics and the transition to turbulence of confined active nematics, Proc. Natl. Acad. Sci. U S A 116, 4788 (2019)

    work page 2019

  27. [27]

    Hardo¨ uin, R

    J. Hardo¨ uin, R. Hughes, A. Doostmohammadi, J. Lau- rent, T. Lopez-Leon, J. M. Yeomans, J. Ign´ es-Mullol, and F. Sagu´ es, Reconfigurable flows and defect landscape of confined active nematics, Communications Physics 2, 10.1038/s42005-019-0221-x (2019)

    work page doi:10.1038/s42005-019-0221-x 2019

  28. [28]

    Hardouin, J

    J. Hardouin, J. Laurent, T. Lopez-Leon, J. Ignes-Mullol, and F. Sagues, Active microfluidic transport in two- dimensional handlebodies, Soft Matter 16, 9230 (2020)

    work page 2020

  29. [29]

    Guillamat, J

    P. Guillamat, J. Ignes-Mullol, and F. Sagues, Control of active liquid crystals with a magnetic field, Proc. Natl. Acad. Sci. U S A 113, 5498 (2016)

    work page 2016

  30. [30]

    Sunyer, V

    R. Sunyer, V. Conte, J. Escribano, A. Elosegui-Artola, A. Labernadie, L. Valon, D. Navajas, J. M. Garcia- Aznar, J. J. Munoz, P. Roca-Cusachs, and X. Trepat, Collective cell durotaxis emerges from long-range inter- cellular force transmission, Science 353, 1157 (2016)

    work page 2016

  31. [31]

    Zhang, S

    R. Zhang, S. A. Redford, P. V. Ruijgrok, N. Kumar, A. Mozaffari, S. Zemsky, A. R. Dinner, V. Vitelli, Z. Bryant, M. L. Gardel, and J. J. de Pablo, Spatiotem- poral control of liquid crystal structure and dynamics through activity patterning, Nat Mater (2021)

    work page 2021

  32. [32]

    Caballero, J

    D. Caballero, J. Comelles, M. Piel, R. Voituriez, and D. Riveline, Ratchetaxis: Long-range directed cell mi- gration by local cues, Trends Cell Biol 25, 815 (2015)

    work page 2015

  33. [33]

    Sokolov, M

    A. Sokolov, M. M. Apodaca, B. A. Grzybowski, and I. S. Aranson, Swimming bacteria power microscopic gears, Proc. Natl. Acad. Sci. U S A 107, 969 (2010)

    work page 2010

  34. [34]

    V´ elez-Cer´ on, P

    I. V´ elez-Cer´ on, P. Guillamat, F. Sagu´ es, and J. Ign´ es- Mullol, Probing active nematics with in situ microfab- ricated elastic inclusions, Proc. Natl. Acad. Sci. U S A 121, e2312494121 (2024)

    work page 2024

  35. [35]

    R. C. V. Coelho, N. A. M. Ara´ ujo, and M. M. Telo da Gama, Dispersion of activity at an active–passive ne- matic interface, Soft Matter 18, 7642 (2022)

    work page 2022

  36. [36]

    Green, J

    R. Green, J. Toner, and V. Vitelli, Geometry of thresh- oldless active flow in nematic microfluidics, Physical Re- view Fluids 2 (2017)

    work page 2017

  37. [37]

    Hardo¨ uin, C

    J. Hardo¨ uin, C. Dor´ e, J. Laurent, T. Lopez-Leon, J. Ign´ es-Mullol, and F. Sagu´ es, Active boundary layers in confined active nematics, Nature Communications 13, 6675 (2022)

    work page 2022

  38. [38]

    C. D. Schimming, C. J. O. Reichhardt, and C. Reich- hardt, Vortex lattices in active nematics with periodic obstacle arrays, Phys Rev Lett 132, 018301 (2024)

    work page 2024

  39. [39]

    C. D. Schimming, C. J. O. Reichhardt, and C. Reich- hardt, Active nematic ratchet in asymmetric obstacle ar- rays, Physical Review E 109 (2024)

    work page 2024

  40. [40]

    Giomi, Geometry and topology of turbulence in active nematics, Physical Review X 5, 031003 (2015)

    L. Giomi, Geometry and topology of turbulence in active nematics, Physical Review X 5, 031003 (2015)

    work page 2015

  41. [41]

    R. R. Keogh, T. Kozhukhov, K. Thijssen, and T. N. Shen- druk, Active darcy’s law, Physical Review Letters 132 (2024)

    work page 2024

  42. [42]

    I. J. Karassik, J. P. Messina, P. Cooper, and C. C. Heald, eds., Pump Handbook, 4th ed. (McGraw-Hill Education, New York, 2008)

    work page 2008

  43. [43]

    Nguyen and Z

    N.-T. Nguyen and Z. Wu, Micromixers—a review, Jour- nal of Micromechanics and Microengineering 15, R1 (2005)

    work page 2005

  44. [44]

    Squires and S

    T. Squires and S. Quake, Microfluidics: Fluid physics at the nanoliter scale, Reviews of Modern Physics 77, 977 (2005)

    work page 2005

  45. [45]

    Peng and J

    Z. Peng and J. F. Brady, Upstream swimming and taylor dispersion of active brownian particles, Physical Review Fluids 5 (2020)

    work page 2020

  46. [46]

    Solute dispersion in pre-turbulent confined active nematics

    T. Alvim, M. M. T. da Gama, and R. C. V. Coelho, So- lute dispersion in pre-turbulent confined active nematics (2024), arXiv:2410.04629 [cond-mat.soft]

    work page internal anchor Pith review Pith/arXiv arXiv 2024

  47. [47]

    Jorge, A

    C. Jorge, A. Chardac, A. Poncet, and D. Bartolo, Ac- tive hydraulics laws from frustration principles, Nature Physics 20, 303 (2024)

    work page 2024

  48. [48]

    Ign´ es-Mullol, Active nematic emulsions (2025), open Science Framework

    J. Ign´ es-Mullol, Active nematic emulsions (2025), open Science Framework. https://osf.io/n8g4c/. Deposited 7 January 2025

    work page 2025

  49. [49]

    P. W. Ellis, J. Nambisan, and A. Fernandez- Nieves, Coherence-enhanced diffusion filtering applied to partially-ordered fluids, Molecular Physics 118, 1 (2020)

    work page 2020

  50. [50]

    S. P. Thampi, A. Doostmohammadi, R. Golestanian, and J. M. Yeomans, Intrinsic free energy in active nematics, Europhysics Letters 112, 28004 (2015)

    work page 2015

  51. [51]

    R. C. Coelho, J. A. Moreira, D. M. Pedro, and M. M. T. da Gama, Active nematic-isotropic interfaces on flat sur- faces: Effects of anchoring, ordering field and activity, Giant 19, 100309 (2024)

    work page 2024

  52. [52]

    A. N. Beris and B. J. Edwards, Thermodynamics of flow- ing systems: with internal microstructure , 36 (Oxford University Press, USA, 1994)

    work page 1994

  53. [53]

    Aditi Simha and S

    R. Aditi Simha and S. Ramaswamy, Hydrodynamic fluc- tuations and instabilities in ordered suspensions of self- propelled particles, Phys. Rev. Lett. 89, 058101 (2002)

    work page 2002

  54. [54]

    R. C. V. Coelho, N. A. M. Ara´ ujo, and M. M. Telo da 13 Gama, Active nematic–isotropic interfaces in channels, Soft Matter 15, 6819 (2019)

    work page 2019

  55. [55]

    Saghatchi, M

    R. Saghatchi, M. Yildiz, and A. Doostmohammadi, Ne- matic order condensation and topological defects in iner- tial active nematics, Phys. Rev. E 106, 014705 (2022)

    work page 2022

  56. [56]

    M. R. Nejad and J. M. Yeomans, Active extensile stress promotes 3d director orientations and flows, Phys Rev Lett 128, 048001 (2022)

    work page 2022

  57. [57]

    Marenduzzo, E

    D. Marenduzzo, E. Orlandini, M. Cates, and J. Yeomans, Steady-state hydrodynamic instabilities of active liquid crystals: Hybrid lattice boltzmann simulations, Physical Review E 76, 031921 (2007)

    work page 2007