Quantification of surface tension and internal pressure generated by single mitotic cells

Area of Science:

• Cell biology
• Biophysics
• Mechanobiology

Background:

• During mitosis, adherent cells undergo significant shape changes, rounding up due to actomyosin cortex tension and increased internal hydrostatic pressure.
• Laplace's law relates surface tension, local curvature, and hydrostatic pressure difference in a liquid cell interior, but experimental verification in cells is challenging.
• Accurate measurement of cell shape and mechanical forces is crucial for understanding these cellular processes.

Purpose of the Study:

• To accurately measure the internal hydrostatic pressure excess and surface tension of single cells during different cell cycle phases.
• To validate the applicability of Laplace's law to describe the shape and mechanics of confined cells.
• To introduce a novel method for characterizing the mechanical properties of rounded cells.

Main Methods:

• Utilized wedged micro-cantilevers to uniaxially confine single HeLa cells, measuring confinement forces.
• Employed confocal microscopy to concurrently determine the precise shape of confined cells.
• Fitted experimental cell shapes to theoretical models based on Laplace's law with uniform surface tension.

Main Results:

• Quantitative agreement was found between experimentally measured confined cell shapes and those predicted by Laplace's law.
• Calculated hydrostatic pressure excess and surface tension using geometrical parameters and measured forces.
• HeLa cells exhibited a significant increase in hydrostatic pressure excess (≈ 40 Pa to ≈ 400 Pa) and surface tension (≈ 0.2 mNm⁻¹ to ≈ 1.6 mNm⁻¹) from interphase to metaphase.

Conclusions:

• The introduced method accurately determines the internal pressure excess and surface tension of rounded cells with minimal perturbation.
• The findings quantitatively support the application of Laplace's law in describing cell mechanics during mitosis.
• This approach offers a versatile tool for characterizing the mechanical properties of diverse cellular systems.