Real-time imaging of cellular forces using optical interference

Abstract

Important dynamic processes in mechanobiology remain elusive due to a lack of tools to image the small cellular forces at play with sufficient speed and throughput. Here, we introduce a fast, interference-based force imaging method that uses the illumination of an elastic deformable microcavity with two rapidly alternating wavelengths to map forces. We show real-time acquisition and processing of data, obtain images of mechanical activity while scanning across a cell culture, and investigate sub-second fluctuations of the piconewton forces exerted by macrophage podosomes. We also demonstrate force imaging of beating neonatal cardiomyocytes at 100 fps which reveals mechanical aspects of spontaneous oscillatory contraction waves in between the main contraction cycles. These examples illustrate the wider potential of our technique for monitoring cellular forces with high throughput and excellent temporal resolution.

Nanoscale Tracking Combined with Cell-Scale Microrheology Reveals Stepwise Increases in Force Generated by Cancer Cell Protrusions

“…Cancer-cell protrusions exhibit dynamics on a range of time scales from seconds to minutes, as protrusion extension and migration movement involve fast-acting cytoskeletal polymerization. , Therefore, we monitored the force dynamics of the protrusions at an imaging time resolution on the order of seconds to minutes (Figure ), which has previously been done only in 2D cultures or microcavities . At Δt = 1 min imaging intervals, the cancer cells were found to generate forces in two phases that consist of resting phases punctuated by bursts of force exertion (Figure a).…”

“…24,66 Therefore, we monitored the force dynamics of the protrusions at an imaging time resolution on the order of seconds to minutes (Figure 4), which has previously been done only in 2D cultures 31 or microcavities. 67 At Δt = 1 min imaging intervals, the cancer cells were found to generate forces in two phases that consist of resting phases punctuated by bursts of force exertion (Figure 4a). The results indicate that individual forces by a protrusion are dynamically exerted at the sub-nanoNewton scale over intervals lasting ≥60 s (Figures 4b−c), and the resting phase can take up to 6 min (Table S9).…”

Optical mapping of ground reaction force dynamics in freely behavingDrosophila melanogasterlarvae

“…First, we confirmed that the ordinary larval behaviour observed on agarose substrates is maintained when using a collagen-treated microcavity as the substrate ( Supplementary Figure S3 ). We then used WARP (Meek et al, 2021) to enable imaging of substrate interactions at sufficiently high temporal resolution (for details of WARP analysis, see Supplementary Figure S4) . First, we examined protopodial indentations during forward peristaltic waves.…”

“…See Supporting Information Fig. S4 and (Meek et al, 2021) for further details on the calculation of displacement from the λ and λ θ images. All WARP and ERISM images were acquired using an Andor Zyla 4.2 sCMOS camera (Andor Technology, Belfast, UK).…”

“…Many advances in cellular mechanobiology have been fuelled by the development of new force measuring techniques that allow optical measurement of GRFs (reviewed in Mohammed et al, 2019). For example, Elastic Resonator Interference Stress Microscopy (ERISM) (Kronenberg et al, 2017a) and a variant, Wavelength Alternating Resonance Pressure microscopy (WARP) (Meek et al, 2021) enable optical mapping of GRFs in the nanonewton range with micrometre and millisecond precision by monitoring local changes in the optical resonances of soft and deformable microcavities, including in very small, low force structures (Dalaka et al, 2020).…”