The Optical Stretcher: A Novel Laser Tool to Micromanipulate Cells

Abstract

When a dielectric object is placed between two opposed, nonfocused laser beams, the total force acting on the object is zero but the surface forces are additive, thus leading to a stretching of the object along the axis of the beams. Using this principle, we have constructed a device, called an optical stretcher, that can be used to measure the viscoelastic properties of dielectric materials, including biologic materials such as cells, with the sensitivity necessary to distinguish even between different individual cytoskeletal phenotypes. We have successfully used the optical stretcher to deform human erythrocytes and mouse fibroblasts. In the optical stretcher, no focusing is required, thus radiation damage is minimized and the surface forces are not limited by the light power. The magnitude of the deforming forces in the optical stretcher thus bridges the gap between optical tweezers and atomic force microscopy for the study of biologic materials.

Long‐distance laser propulsion and deformation‐ monitoring of cells in optofluidic photonic crystal fiber

“…Moreover, the fact that the initial values of x are independent of power suggests that no instantaneous cell deformation due to optical stretching forces takes place. This is in agreement with the calculations in [16], where it is shown that for a large ratio of optical mode diameter to (spherical) cell thickness, optical stretching forces by a single beam are negligibly small. Surprisingly, however, x changes dynamically as the cell progresses along the fiber, proving that extensive cellular deformation must be taking place.…”

“…The values obtained for the optical forces are in reasonable agreement with Refs. [16,23]. Our results show that the optofluidic mobility of a laser-driven RBC is indeed an intricate combination of the actions of optical and viscous drag forces.…”

“…Several of the techniques for investigating cellular mechanics [12][13][14] make use of optical trapping techniques. For example, Guck and coworkers showed that single cells can be stretched by strong optical forces [15,16] …”

An historical perspective on cell mechanics

“…Recently, AFM has been used to measure the protrusive forces [44,154] at the edge of migrating cells in complement to traction force assays [155,156], micropipette and laser trap studies [157]. Migration is a key element in cancer metastasis, and in recent years, cells have been optically trapped and stretched in electromagnetic fields to measure mechanical properties in relation to metastatic potential [158][159][160][161] (complementary to early deformability assays [162]). In addition, magnetic traps have been utilized to perform rheological measurements with magnetic beads [20, [163][164][165].…”

Recent advances in microfluidic techniques for single-cell biophysical characterization

“…66 The setup was then demonstrated to stretch BALB 3T3 fibroblasts and measure their viscoelastic properties. 67 A typical optical stretcher system consists of a microchannel for loading cells into the testing region and two laser fibers located on the sides of the passageway (see Fig. 2(a)).…”