Monitoring of laser micromanipulated optically trapped cells by digital holographic microscopy.

For a precise manipulation of particles and cells with laser light as well as for the understanding and the control of the underlying processes it is important to visualize and quantify the response of the specimens. Thus, we investigated if digital holographic microscopy (DHM) can be used in combination with microfluidics to observe optically trapped living cells in a minimally invasive fashion during laser micromanipulation. The obtained results demonstrate that DHM multi-focus phase contrast provides label-free quantitative monitoring of optical manipulation with a temporal resolution of a few milliseconds.

The regulatory role of cell mechanics for migration of differentiating myeloid cells.

Migration of cells is important for tissue maintenance, immune response, and often altered in disease. While biochemical aspects, including cell adhesion, have been studied in detail, much less is known about the role of the mechanical properties of cells. Previous measurement methods rely on contact with artificial surfaces, which can convolute the results.

High-throughput rheological measurements with an optical stretcher.

The cytoskeleton is a major determinant of the mechanical strength and morphology of most cells. The composition and assembly state of this intracellular polymer network evolve during the differentiation of cells, and the structure is involved in many cellular functions and is characteristically altered in many diseases, including cancer. Here we exploit the deformability of the cytoskeleton as a link between molecular structure and biological function, to distinguish between cells in different states by using a laser-based optical stretcher (OS) coupled with microfluidic handling of cells.

Reconfigurable microfluidic integration of a dual-beam laser trap with biomedical applications.

A dual-beam fiber laser trap, termed the optical stretcher when used to deform objects, has been combined with a capillary-based microfluidic system in order to serially trap and deform biological cells. The design allows for control over the size and position of the trap relative to the flow channel. Data is recorded using video phase contrast microscopy and is subsequently analyzed using a custom edge fitting routine.

Muller cells are living optical fibers in the vertebrate retina.

Although biological cells are mostly transparent, they are phase objects that differ in shape and refractive index. Any image that is projected through layers of randomly oriented cells will normally be distorted by refraction, reflection, and scattering. Counterintuitively, the retina of the vertebrate eye is inverted with respect to its optical function and light must pass through several tissue layers before reaching the light-detecting photoreceptor cells.

Quantifying the contribution of actin networks to the elastic strength of fibroblasts.

The structural models created to understand the cytoskeletal mechanics of cells in suspension are described here. Suspended cells can be deformed by well-defined surface stresses in an Optical Stretcher [Guck, J., Ananthakrishnan, R.

Characterizing single suspended cells by optorheology.

The measurement of the mechanical properties of individual cells has received much attention in recent years. In this paper we describe the application of optically induced forces with an optical stretcher to perform step-stress experiments on individual suspended fibroblasts. The conversion from creep-compliance to frequency-dependent complex shear modulus reveals characteristic viscoelastic signatures of the underlying cytoskeleton and its dynamic molecular properties.

Optical rheology of biological cells.

A step stress deforming suspended cells causes a passive relaxation, due to a transiently cross-linked isotropic actin cortex underlying the cellular membrane. The fluid-to-solid transition occurs at a relaxation time coinciding with unbinding times of actin cross-linking proteins. Elastic contributions from slowly relaxing entangled filaments are negligible.

Optical deformability as an inherent cell marker for testing malignant transformation and metastatic competence.

The relationship between the mechanical properties of cells and their molecular architecture has been the focus of extensive research for decades. The cytoskeleton, an internal polymer network, in particular determines a cell's mechanical strength and morphology. This cytoskeleton evolves during the normal differentiation of cells, is involved in many cellular functions, and is characteristically altered in many diseases, including cancer.

Deformability-based flow cytometry.

Background: Elasticity of cells is determined by their cytoskeleton. Changes in cellular function are reflected in the amount of cytoskeletal proteins and their associated networks. Drastic examples are diseases such as cancer, in which the altered cytoskeleton is even diagnostic.