Measurement of the traction force of biological cells by digital holography

Abstract

The traction force produced by biological cells has been visualized as distortions in flexible substrata. We have utilized quantitative phase microscopy by digital holography (DH-QPM) to study the wrinkling of a silicone rubber film by motile fibroblasts. Surface deformation and the cellular traction force have been measured from phase profiles in a direct and straightforward manner. DH-QPM is shown to provide highly efficient and versatile means for quantitatively analyzing cellular motility.

Keywords: (090.1995) Digital holography; (170.0180) Microscopy; (170.3880) Medical and biological imaging.

Fig. 1

DHM setup. M’s: mirrors; BS’s: beam splitters; MO’s: microscope objectives; S: sample object

Fig. 2

Schematic of the cell-substrate sample (lower) and the corresponding optical thickness profile (upper).

Fig. 3

DHM analysis of fibroblasts wrinkling the silicone rubber film. The field of view is 190 × 176 μm² with 800 × 742 pixels. a) Hologram; b) Angular spectrum; c) Amplitude image; d) Quantitative phase image; e) Bright field image.

Fig. 4

Multimode imaging from a single hologram. The field of view is 190 × 176 μm² with 800 × 742 pixels. a) dark field; b) Zernike+; c) Zernike–; d) DIC; e) spiral DIC.

Fig. 5

Examples of cells wrinkling a silicone rubber film. The field of view was 190 × 176 μm² with 800 × 742 pixels. a), e) and i) Bright field images; b), f) and j) Quantitative phase images; c), g) and k) Cross-sections of phase profiles along highlighted lines AB in b), CD in f) and EF in j); d), h) and l) Pseudo-color 3-D rendering of phase images b), f) and j).

Fig. 6

An excerpt of several frames from phase movie recordings of cells wrinkling a silicone rubber film (Media 1). The field of view was 190 × 176 μm² with 800 × 742 pixels. Time interval of two contiguous images above was around 30 min.

Fig. 7

Phase profiles scaled as physical thickness and plotted in proportion to horizontal distance. a) Wrinkled area H from Fig. 5c). b) Wrinkled area I from Fig. 5g). c) Wrinkled area J from Fig. 3k). In each case, the average of 10 adjacent profiles is presented.