Skip to main content

Thank you for visiting You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

Intracellular softening and increased viscoelastic fluidity during division


The life and death of an organism rely on correct cell division, which occurs through the process of mitosis. Although the biochemical signalling and morphogenetic processes during mitosis are well understood, the importance of mechanical forces and material properties is only just starting to be discovered. Recent studies have revealed that the layer of proteins beneath the cell membrane—the so-called cell cortex—stiffens during mitosis, but it is as yet unclear whether mechanical changes occur in the rest of the material in the cell, contained in the cytoplasm. Here we show that, in contrast to the cortical stiffening, the interior of the cell undergoes a softening and an increase in dissipative timescale, similar to viscoelastic relaxation. These mechanical changes are accompanied by a decrease in the active forces that drive particle mobility. Using optical tweezers to perform microrheology measurements, we capture the complex active and passive material states of the cytoplasm using six relevant parameters, of which only two vary considerably during mitosis. We demonstrate a role switch between microtubules and actin that could contribute to the observed softening.

This is a preview of subscription content, access via your institution

Access options

Buy article

Get time limited or full article access on ReadCube.


All prices are NET prices.

Fig. 1: Intracellular viscoelasticity during the cell cycle.
Fig. 2: Spontaneous fluctuations and active energy in interphase and dividing cells.
Fig. 3: Comparison of viscoelasticity and activity in interphase and mitotic cells under cytoskeletal drugs.
Fig. 4: Model of intracellular mechanics in interphase and mitosis.

Data availability

Source data are provided with this paper.

Code availability

Python code used for analysing active microrheological and fluctuation analysis data is available at


  1. Moulding, D. A. et al. Excess F-actin mechanically impedes mitosis leading to cytokinesis failure in X-linked neutropenia by exceeding Aurora B kinase error correction capacity. Blood 120, 3803–3811 (2012).

    Article  Google Scholar 

  2. Levine, M. S. & Holland, A. J. The impact of mitotic errors on cell proliferation and tumorigenesis. Genes Dev. 32, 620–638 (2018).

    Article  Google Scholar 

  3. Strangeways, T. S. P. Observations on the changes seen in living cells during growth and division. Proc. R. Soc. Lond. B 94, 137–141 (1922).

    Article  ADS  Google Scholar 

  4. Lancaster, O. M. et al. Mitotic rounding alters cell geometry to ensure efficient bipolar spindle formation. Dev. Cell 25, 270–283 (2013).

    Article  Google Scholar 

  5. Cadart, C., Zlotek-Zlotkiewicz, E., Le Berre, M., Piel, M. & Matthews, H. K. Exploring the function of cell shape and size during mitosis. Dev. Cell 29, 159–169 (2014).

    Article  Google Scholar 

  6. Zlotek-Zlotkiewicz, E., Monnier, S., Cappello, G., Le Berre, M. & Piel, M. Optical volume and mass measurements show that mammalian cells swell during mitosis. J. Cell Biol. 211, 765–774 (2015).

    Article  Google Scholar 

  7. Champion, L., Linder, M. I. & Kutay, U. Cellular reorganization during mitotic entry. Trends. Cell Biol. 27, 26–41 (2017).

    Article  Google Scholar 

  8. Niethammer, P. et al. Discrete states of a protein interaction network govern interphase and mitotic microtubule dynamics. PLoS Biol. 5, e29 (2007).

    Article  Google Scholar 

  9. Mchedlishvili, N., Matthews, H. K., Corrigan, A. & Baum, B. Two-step interphase microtubule disassembly aids spindle morphogenesis. BMC Biol. 16, 14 (2018).

    Article  Google Scholar 

  10. Taubenberger, A. V., Baum, B. & Matthews, H. K. The mechanics of mitotic cell rounding. Front. Cell Dev. Biol. 8, 687 (2020).

    Article  Google Scholar 

  11. Stewart, M. P. et al. Hydrostatic pressure and the actomyosin cortex drive mitotic cell rounding. Nature 469, 226–230 (2011).

    Article  ADS  Google Scholar 

  12. Fischer-Friedrich, E. et al. Rheology of the active cell cortex in mitosis. Biophys. J. 111, 589–600 (2016).

    Article  ADS  Google Scholar 

  13. Sorce, B. et al. Mitotic cells contract actomyosin cortex and generate pressure to round against or escape epithelial confinement. Nat. Commun. 6, 8872 (2015).

    Article  ADS  Google Scholar 

  14. Cattin, C. J. et al. Mechanical control of mitotic progression in single animal cells. Proc. Natl Acad. Sci. USA 112, 11258–11263 (2015).

    Article  ADS  Google Scholar 

  15. Nicklas, R. B. Measurements of the force produced by the mitotic spindle in anaphase. J. Cell Biol. 97, 542–548 (1983).

    Article  Google Scholar 

  16. Brugués, J. & Needleman, D. Physical basis of spindle self-organization. Proc. Natl Acad. Sci. USA 111, 18496–18500 (2014).

    Article  ADS  Google Scholar 

  17. Garzon-Coral, C., Fantana, H. A. & Howard, J. A force-generating machinery maintains the spindle at the cell center during mitosis. Science 352, 1124–1127 (2016).

    Article  ADS  Google Scholar 

  18. Grill, S. W. & Hyman, A. A. Spindle positioning by cortical pulling forces. Dev. Cell 8, 461–465 (2005).

    Article  Google Scholar 

  19. Pavin, N. & Tolić, I. M. Mechanobiology of the mitotic spindle. Dev. Cell 56, 192–201 (2021).

    Article  Google Scholar 

  20. Oriola, D., Needleman, D. J. & Brugués, J. The physics of the metaphase spindle. Annu. Rev. Biophys. 47, 655–673 (2018).

    Article  Google Scholar 

  21. Nazockdast, E. & Redemann, S. Mechanics of the spindle apparatus. Semin. Cell Dev. Biol. 107, 91–102 (2020).

    Article  Google Scholar 

  22. Moore, A. S. et al. Actin cables and comet tails organize mitochondrial networks in mitosis. Nature 591, 659–664 (2021).

    Article  ADS  Google Scholar 

  23. Mizuno, D., Tardin, C., Schmidt, C. F. & MacKintosh, F. C. Nonequilibrium mechanics of active cytoskeletal networks. Science 315, 370–373 (2007).

    Article  ADS  Google Scholar 

  24. Stamenović, D. et al. Rheological behavior of living cells is timescale-dependent. Biophys. J. 93, L39–L41 (2007).

    Article  Google Scholar 

  25. Ahmed, W. W. et al. Active mechanics reveal molecular-scale force kinetics in living oocytes. Biophys. J. 114, 1667–1679 (2018).

    Article  ADS  Google Scholar 

  26. Bonfanti, A., Kaplan, J. L., Charras, G. & Kabla, A. Fractional viscoelastic models for power-law materials. Soft Matter 16, 6002–6020 (2020).

    Article  ADS  Google Scholar 

  27. Yamada, S., Wirtz, D. & Kuo, S. C. Mechanics of living cells measured by laser tracking microrheology. Biophys. J. 78, 1736–1747 (2000).

    Article  Google Scholar 

  28. Kollmannsberger, P. & Fabry, B. Linear and nonlinear rheology of living cells. Annu. Rev. Mater. Res. 41, 75–97 (2011).

    Article  ADS  Google Scholar 

  29. Fabry, B. et al. Time scale and other invariants of integrative mechanical behavior in living cells. Phys. Rev. E 68, 041914 (2003).

    Article  ADS  Google Scholar 

  30. Trepat, X., Lenormand, G. & Fredberg, J. J. Universality in cell mechanics. Soft Matter 4, 1750–1759 (2008).

    Article  ADS  Google Scholar 

  31. Hoffman, B. D. & Crocker, J. C. Cell mechanics: dissecting the physical responses of cells to force. Annu. Rev. Biomed. Eng. 11, 259–288 (2009).

    Article  Google Scholar 

  32. Desprat, N., Richert, A., Simeon, J. & Asnacios, A. Creep function of a single living cell. Biophys. J. 88, 2224–2233 (2005).

    Article  Google Scholar 

  33. Deng, L. et al. Fast and slow dynamics of the cytoskeleton. Nat. Mater. 5, 636–640 (2006).

    Article  ADS  Google Scholar 

  34. Rigato, A., Miyagi, A., Scheuring, S. & Rico, F. High-frequency microrheology reveals cytoskeleton dynamics in living cells. Nat. Phys. 13, 771–775 (2017).

    Article  Google Scholar 

  35. Nishizawa, K. et al. Feedback-tracking microrheology in living cells. Sci. Adv. 3, e1700318 (2017).

    Article  ADS  Google Scholar 

  36. Mezger, T. G. The Rheology Handbook 4th edn (Vincentz Network, 2012).

  37. Moeendarbary, E. et al. The cytoplasm of living cells behaves as a poroelastic material. Nat. Mater. 12, 253–261 (2013).

    Article  ADS  Google Scholar 

  38. MacKintosh, F. C. & Levine, A. J. Nonequilibrium mechanics and dynamics of motor-activated gels. Phys. Rev. Lett. 100, 018104 (2008).

    Article  ADS  Google Scholar 

  39. Krall, A. H. & Weitz, D. A. Internal dynamics and elasticity of fractal colloidal gels. Phys. Rev. Lett. 80, 778–781 (1998).

    Article  ADS  Google Scholar 

  40. Guo, M. et al. Probing the stochastic, motor-driven properties of the cytoplasm using force spectrum microscopy. Cell 158, 822–832 (2014).

    Article  Google Scholar 

  41. Turlier, H. et al. Equilibrium physics breakdown reveals the active nature of red blood cell flickering. Nat. Phys. 12, 513–519 (2016).

    Article  Google Scholar 

  42. Xie, J. & Minc, N. Cytoskeleton force exertion in bulk cytoplasm. Front. Cell Dev. Biol. 8, 69 (2020).

    Article  Google Scholar 

  43. Mayer, M., Depken, M., Bois, J. S., Jülicher, F. & Grill, S. W. Anisotropies in cortical tension reveal the physical basis of polarizing cortical flows. Nature 467, 617–621 (2010).

    Article  ADS  Google Scholar 

  44. Shamipour, S. et al. Bulk actin dynamics drive phase segregation in zebrafish oocytes. Cell 177, 1463–1479 (2019).

    Article  Google Scholar 

  45. Skoufias, D. A. et al. S-trityl-l-cysteine is a reversible, tight binding inhibitor of the human kinesin Eg5 that specifically blocks mitotic progression. J. Biol. Chem. 281, 17559–17569 (2006).

    Article  Google Scholar 

  46. Mason, T. G. & Weitz, D. A. Optical measurements of frequency-dependent linear viscoelastic moduli of complex fluids. Phys. Rev. Lett. 74, 1250–1253 (1995).

    Article  ADS  Google Scholar 

  47. Nguyen, A., Brandt, M., Muenker, T. M. & Betz, T. Multi-oscillation microrheology via acoustic force spectroscopy enables frequency-dependent measurements on endothelial cells at high-throughput. Lab Chip 21, 1929–1947 (2021).

    Article  Google Scholar 

  48. Sollich, P., Lequeux, F., Hébraud, P. & Cates, M. E. Rheology of soft glassy materials. Phys. Rev. Lett. 78, 2020–2023 (1997).

    Article  ADS  Google Scholar 

  49. Caputo, M. Linear models of dissipation whose Q is almost frequency independent—II. Geophys. J. Int. 13, 529–539 (1967).

    Article  ADS  Google Scholar 

Download references


We thank T. Münker for technical support and helpful discussions. We are thankful for critical comments by E. Raz and M. Reichman-Fried. We thank R. Wedlich-Söldner for the MDCK II cell line expressing H2B-mCherry and GFP-LifeAct and the HeLa line expressing H2B-mCherry, and we thank A. Sivan for his help generating patterns. We thank C. Brennecka for critical revision of the manuscript. S.H., M.B. and T.B. were supported by the Interdisciplinary Center for Clinical Research (IZKF) Münster (Bet1/013/17). T.B. was supported by the European Research Council ERC-Consolidator grant PolarizeMe (771201) and by the DFG under Germany’s Excellence Strategy (EXC 2067/1- 390729940).

Author information

Authors and Affiliations



S.H. designed the study, carried out experiments and analysed data. B.E.V. and M.B. contributed to the experiments and provided helpful discussions. T.B. analysed data and designed and supervised the study. All authors wrote the manuscript.

Corresponding author

Correspondence to Timo Betz.

Ethics declarations

Competing interests

The authors declare no competing interests.

Additional information

Peer review informationNature Physics thanks Dimitrije Stamenovic and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Extended data

Extended Data Fig. 1 Extension of fractional Kelvin-Voigt model.

Extension of the fractional Kelvin-Voigt model from Fig. 1c. Data points and grey region are displayed in Fig. 1c.

Extended Data Fig. 2 Intracellular viscoelasticity and activity in dividing HeLa cells.

The parameters show a similar behaviour of mechanical properties as in MDCK cells. a) Power-law exponents α and β of viscoelastic fit for different phases of mitosis. b) Prefactor cα of viscoelastic fit. c) Prefactor cβ of viscoelastic fit. d) Prefactor e0 of power-law fit to active energy. e) Power-law exponent ν of fit to active energy. ncells: 20, 11, 23, 11, 10.

Source data

Extended Data Fig. 3 Intracellular viscoelasticity and activity dependence on cell shape.

Interphase cells forced into a round shape comparable to dividing cells show increased stiffness. a) Fluorescent images of interphase cell forced into a round shape (left), cell in metaphase (middle) and cell arrested in mitosis by STC (right). Red: H2B; cyan: actin. b) Prefactors cα, cβ and e0. cα shows drastic increase of stiffness in interphase cells forced into a round shape. c) Exponents α, β and ν. Only ν shows a significant increase, which is not seen in mitotic cells. d) Fold changes of all parameters of cells forced into a round shape compared to flat interphase cells. Error bars indicate normalized error. The found differences cannot explain the changes found in mitotic cells. In round interphase cells stiffness increases, while stiffness drastically decreases in mitotic cells. ncells: 57, 63.

Source data

Extended Data Fig. 4 Comparison of passive and active mechanical parameters of MDCK cells in prophase and arrested in mitosis by STC.

The parameters do not show a significant difference between cells in prophase and cells treated with STC, which arrests the cells in mitosis. ncells: 15, 36. Data shows mean ± SE.

Source data

Extended Data Fig. 5 Comparison of material property parameters in mitotic cells after treatment with different actin drugs.

Treatment with cytochalasin B (20.9 μM), cytochalasin D (10 μM) and latrunculin A (474 nM) all lead to similar parameters. ncells: 55, 58, 47.

Source data

Extended Data Fig. 6 Radial intensity of actin and microtubules around particles.

Top: Immunostained cells in interphase and treated with STC; blue: nucleus, Hoechst; red: microtubules, anti-α-tubulin; cyan: actin, phalloidin; magenta: 1 μm particle, covalently bound dye. The yellow circle indicates the area around the particle that was analysed. Bottom: mean radial intensity of particle, actin and microtubule signal of 21 particles in interphase cells (left) and 10 particles in STC treated cells (right). Error indicates SD.

Source data

Supplementary information

Reporting Summary

Supplementary Table 1.

Parameters of fractional viscoelastic fits to MDCK and HeLa cells.

Source data

Source Data Fig. 1

Statistical source data for Fig. 1.

Source Data Fig. 2

Statistical source data for Fig. 2.

Source Data Fig. 3

Statistical source data for Fig. 3.

Source Data Extended Data Fig. 2

Statistical source data for Extended Data Fig. 2.

Source Data Extended Data Fig. 3

Statistical source data for Extended Data Fig. 3

Source Data Extended Data Fig. 4

Statistical source data for Extended Data Fig. 4.

Source Data Extended Data Fig. 5

Statistical source data for Extended Data Fig. 5.

Source Data Extended Data Fig. 6

Statistical source data for Extended Data Fig. 6.

Rights and permissions

Reprints and Permissions

About this article

Verify currency and authenticity via CrossMark

Cite this article

Hurst, S., Vos, B.E., Brandt, M. et al. Intracellular softening and increased viscoelastic fluidity during division. Nat. Phys. 17, 1270–1276 (2021).

Download citation

  • Received:

  • Accepted:

  • Published:

  • Issue Date:

  • DOI:


Quick links

Nature Briefing

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing