Living cells as a biological analog of optical tweezers - a non-invasive microrheology approach

William Hardiman; Matt Clark; Claire Friel; Alan Huett; Fernando Pérez-Cota; Kerry Setchfield; Amanda J Wright; Manlio Tassieri

doi:10.1016/j.actbio.2023.04.039

Living cells as a biological analog of optical tweezers - a non-invasive microrheology approach

Acta Biomater. 2023 Aug:166:317-325. doi: 10.1016/j.actbio.2023.04.039. Epub 2023 May 1.

Authors

William Hardiman¹, Matt Clark², Claire Friel³, Alan Huett³, Fernando Pérez-Cota², Kerry Setchfield², Amanda J Wright⁴, Manlio Tassieri⁵

Affiliations

¹ Optics and Photonics Research Group, Faculty of Engineering, University of Nottingham, Nottingham NG7 2RD, UK. Electronic address: will.hardiman@nottingham.ac.uk.
² Optics and Photonics Research Group, Faculty of Engineering, University of Nottingham, Nottingham NG7 2RD, UK.
³ School of Life Sciences, University of Nottingham, Medical School, QMC, Nottingham NG7 2UH, UK.
⁴ Optics and Photonics Research Group, Faculty of Engineering, University of Nottingham, Nottingham NG7 2RD, UK. Electronic address: Amanda.Wright@Nottingham.ac.uk.
⁵ Division of Biomedical Engineering, James Watt School of Engineering, University of Glasgow, Glasgow, G12 8LT, UK. Electronic address: Manlio.Tassieri@Glasgow.ac.uk.

PMID: 37137402
DOI: 10.1016/j.actbio.2023.04.039

Abstract

Microrheology, the study of fluids on micron length-scales, promises to reveal insights into cellular biology, including mechanical biomarkers of disease and the interplay between biomechanics and cellular function. Here a minimally-invasive passive microrheology technique is applied to individual living cells by chemically binding a bead to the surface of a cell, and observing the mean squared displacement of the bead at timescales ranging from milliseconds to 100s of seconds. Measurements are repeated over the course of hours, and presented alongside analysis to quantify changes in the cells' low-frequency elastic modulus, G₀^', and the cell's dynamics over the time window ∼10^-2 s to 10 s. An analogy to optical trapping allows verification of the invariant viscosity of HeLa S3 cells under control conditions and after cytoskeletal disruption. Stiffening of the cell is observed during cytoskeletal rearrangement in the control case, and cell softening when the actin cytoskeleton is disrupted by Latrunculin B. These data correlate with conventional understanding that integrin binding and recruitment triggers cytoskeletal rearrangement. This is, to our knowledge, the first time that cell stiffening has been measured during focal adhesion maturation, and the longest time over which such stiffening has been quantified by any means. STATEMENT OF SIGNIFICANCE: Here, we present an approach for studying mechanical properties of live cells without applying external forces or inserting tracers. Regulation of cellular biomechanics is crucial to healthy cell function. For the first time in literature, we can non-invasively and passively quantify cell mechanics during interactions with functionalised surface. Our method can monitor the maturation of adhesion sites on the surface of individual live cells without disrupting the cell mechanics by applying forces to the cell. We observe a stiffening response in cells over tens of minutes after a bead chemically binds. This stiffening reduces the deformation rate of the cytoskeleton, although the internal force generation increases. Our method has potential for applications to study mechanics during cell-surface and cell-vesicle interactions.

Keywords: Cellular biomechanics; Cytoskeleton; Optical tweezers; Passive microrheology.

Publication types

Research Support, Non-U.S. Gov't

MeSH terms

Actin Cytoskeleton
Cell Membrane / metabolism
Cytoskeleton* / metabolism
Elastic Modulus
Optical Tweezers*