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Controlling liquid–liquid phase behaviour with an active fluid

Nature Materials volume 22, pages 1401–1408 (2023)Cite this article

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Abstract

Demixing binary liquids is a ubiquitous transition explained using a well-established thermodynamic formalism that requires the equality of intensive thermodynamics parameters across phase boundaries. Demixing transitions also occur when binary fluid mixtures are driven away from equilibrium, but predicting and designing such out-of-equilibrium transitions remains a challenge. Here we study the liquid–liquid phase separation of attractive DNA nanostars driven away from equilibrium using a microtubule-based active fluid. We find that activity lowers the critical temperature and narrows the range of coexistence concentrations, but only in the presence of mechanical bonds between the liquid droplets and reconfiguring active fluid. Similar behaviours are observed in numerical simulations, suggesting that the activity suppression of the critical point is a generic feature of active liquid–liquid phase separation. Our work describes a versatile platform for building soft active materials with feedback control and providing an insight into self-organization in cell biology.

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Fig. 1: Active LLPS composed of DNA nanostars and MT-based active fluid.
Fig. 2: Activity suppresses LLPS.
Fig. 3: Activity-dependent phase diagram of DNA nanostars.
Fig. 4: LLPS suppression requires MT–droplet interactions.
Fig. 5: MT network couples to DNA droplets.
Fig. 6: Theoretical model of active LLPS.

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Data availability

All data supporting the findings of this study are available within the Article and its Supplementary Information. Source data are provided with this paper.

Code availability

The numerical code used to generate the thermotical phase diagram is available via GitHub at https://github.com/fcaballerop/nematicPhaseFieldFoam.

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Acknowledgements

We thank P. Gulati, Z. You, G. Abraham and S. Takatori for fruitful discussions. We thank N. Mitchell for help with the analysis of the 3D images. This work was primarily supported by the US Department of Energy, Basic Energy Sciences, through award DE-SC001973. The initial stages of the theoretical modelling were supported by NSF-DMR-2041459. We also acknowledge the use of the Brandeis MRSEC Bio-Synthesis Facility, which is supported by NSF-MRSEC-2011846. O.A.S. acknowledges support from the W.M. Keck Foundation. A.M.T. is a Simons Foundation Fellow of the Life Sciences Research Foundation and is an Awardee of the Weizmann Institute of Science–National Postdoctoral Award Program for Advancing Women in Science.

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Authors and Affiliations

  1. Department of Physics, University of California, Santa Barbara, CA, USA

    Alexandra M. Tayar, Fernando Caballero, Trevor Anderberg, Omar A. Saleh, M. Cristina Marchetti & Zvonimir Dogic

  2. Materials Department, University of California, Santa Barbara, CA, USA

    Omar A. Saleh

  3. Biomolecular Science and Engineering Program, University of California, Santa Barbara, CA, USA

    Omar A. Saleh, M. Cristina Marchetti & Zvonimir Dogic

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Contributions

A.M.T., O.A.S. and Z.D. designed the experiments. A.M.T. performed the experimental work and data analysis. T.A. helped with the data analysis. F.C. and M.C.M. developed the theory. A.M.T., M.C.M. and Z.D. wrote the manuscript. All authors edited the manuscript.

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Correspondence to Alexandra M. Tayar or Zvonimir Dogic.

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Nature Materials thanks Steve Granick for his contribution to the peer review of this work.

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Supplementary information

Supplementary Information

Supplementary Figs. 1–7, captions for Videos 1–7 and theoretical model.

Supplementary Video 1

Interaction of DNA nanostar droplets and active fluid. Part 1: DNA droplet with no kinesin–DNA. The droplet is advected by MT flows using traditional streptavidin–biotin motor clusters. Overlaid video of DNA droplet (cyan), embedded in an MT active gel (red). Part 2: dense droplets with no kinesin–DNA are advected and deformed by the reconfigurable MT network powered by kinesin–DNA nanostars in the dilute phase. The video is compatible with the data shown in Fig. 1c. Temperature is 19 °C; kinesin–DNA concentration is 2.5 μM; scale bar, 50 μm. The time stamp on the videos indicates the beginning of acquisition.

Supplementary Video 2

LLPS in passive and active samples during temperature ramp-up. Equilibrium LLPS containing DNA nanostars but no active fluid (left). Data with kinesin–DNA in an active MT gel (right). Kinesin concentration, 2.5 µM. The temperature is indicated on the side panel. Each temperature step lasts for 45 min. Scale bar, 100 µm. The time stamp on the videos indicates the beginning of acquisition.

Supplementary Video 3

Dynamics of LLPS with kinesin–DNA nanostars during ATP depletion. Kinesin–DNA depletes the available ATP, leading to a decrease in the active flow speeds. During the slow down, new DNA droplets form. To visualize the formation of new droplets, the contrast was enhanced, which saturated the large droplets. Videos are taken at T = 19 °C and kinesin–DNA concentration of 3.5 μM. The time stamp on the videos indicates the beginning of acquisition.

Supplementary Video 4

Interactions of a droplet with an active fluid in absence of kinesin–DNA. MT–droplet interactions on the droplet surface in a system lacking kinesin–DNA. The droplet is advected by MT flows using traditional streptavidin–biotin motor clusters. The projection layer of the MTs on the surface of the DNA droplet is 11 μm from the surface. Parts 1–3 show the visualization of MT flows on three different droplets. Temperature is 17 °C, the active fluid speed is between 0.3 and 1.0 μm s–1 and the scale is noted by the axis. The time stamp on the videos indicates the beginning of acquisition.

Supplementary Video 5

Interactions of a droplet with an active fluid in the presence of kinesin–DNA. The visualization of MT–droplet interactions in a kinesin–DNA droplet. The droplet is advected, deformed and broken by MT flows powered by kinesin–DNA in the dilute phase. The droplets align with the long axis of the MT bundles on the interface. Parts 1–3 show the visualization of MT flows on three different droplets. The projection layer of MTs on the surface of the DNA droplet is 5.5 μm from the surface. The videos are complementary to the data shown in Fig. 5b. The temperature is 17.5 °C, the external fluid velocity is 0.25 μm s–1, kinesin concentration is 3.5 μM and the scale bar is noted by the axis. The time stamp on the videos indicates the beginning of acquisition.

Supplementary Video 6

Interfacial velocity profile. Two-dimensional confocal image of beads embedded in a DNA droplet. The droplets are faintly labelled with a YOYO dye. The 200 µm beads are larger than the nanostar’s core-to-core distances, indicating local deformations. Temperature is 17.5 °C; scale bar, 100 μm. Part 1: DNA droplet with no kinesin–DNA. The droplet is advected by active flows, which are generated by streptavidin–kinesin clusters. External fluid velocity is 1 μm s–1. Part 2: droplets in a system with kinesin–DNA nanostars. The droplet is advected and deformed by active flows. Kinesin concentration, 3.5 μM The time stamp on the videos indicates the beginning of acquisition.

Supplementary Video 7

Interfacial flow profile in numerical simulations. Numerical integration inside and outside the coexistence region (using the equation mentioned in the main text). We change activity α between the two runs to cross the coexistence region. Inside the coexistence region: low activity, α = −10 (left), we observe the arrested phase separation described in the main text, in which a fully phase-separated initial state breaks down until it reaches a steady state of very dynamic finite-sized droplets; high activity, α = −50 (right), active stresses are strong enough to stabilize the uniform state, and the system is stirred by the nematic, fully mixing both species. The parameters are aQ = −aϕ = bQ = bϕ = γ = λ = η = 1, K = 5 × 10−6, M = 0.1, k = 0.004. The integration is done on a square lattice of 128 × 128, with a lattice spacing of Δx = 0.1 and a time step of Δt = 0.001.

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Source Data Fig. 4

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Source Data Fig. 5

Numerical source data for Fig. 5.

Source Data Fig. 6

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Tayar, A.M., Caballero, F., Anderberg, T. et al. Controlling liquid–liquid phase behaviour with an active fluid. Nat. Mater. 22, 1401–1408 (2023). https://doi.org/10.1038/s41563-023-01660-8

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