Stochastic force dynamics of the model microswimmer Chlamydomonas reinhardtii: Active forces and energetics.

We study the stochastic force dynamics of a model microswimmer (Chlamydomonas reinhardtii), using a combined experimental, theoretical, and numerical approach. While swimming dynamics have been extensively studied using hydrodynamic approaches, which infer forces from the viscous flow field, we directly measure the stochastic forces generated by the microswimmer using an optical trap via the photon momentum method. We analyze the force dynamics by modeling the microswimmer as a self-propelled particle, à la active matter, and analyze its energetics using methods from stochastic thermodynamics.

Small-scale displacement fluctuations of vesicles in fibroblasts.

The intracellular environment is a dynamic space filled with various organelles moving in all directions. Included in this diverse group of organelles are vesicles, which are involved in transport of molecular cargo throughout the cell. Vesicles move in either a directed or non-directed fashion, often depending on interactions with cytoskeletal proteins such as microtubules, actin filaments, and molecular motors.

Active Mechanics Reveal Molecular-Scale Force Kinetics in Living Oocytes.

Active diffusion of intracellular components is emerging as an important process in cell biology. This process is mediated by complex assemblies of molecular motors and cytoskeletal filaments that drive force generation in the cytoplasm and facilitate enhanced motion. The kinetics of molecular motors have been precisely characterized in vitro by single molecule approaches, but their in vivo behavior remains elusive.

Active cell mechanics: Measurement and theory.

Living cells are active mechanical systems that are able to generate forces. Their structure and shape are primarily determined by biopolymer filaments and molecular motors that form the cytoskeleton. Active force generation requires constant consumption of energy to maintain the nonequilibrium activity to drive organization and transport processes necessary for their function.

Active diffusion positions the nucleus in mouse oocytes.

In somatic cells, the position of the cell centroid is dictated by the centrosome. The centrosome is instrumental in nucleus positioning, the two structures being physically connected. Mouse oocytes have no centrosomes, yet harbour centrally located nuclei.

Active transport of vesicles in neurons is modulated by mechanical tension.

Effective intracellular transport of proteins and organelles is critical in cells, and is especially important for ensuring proper neuron functionality. In neurons, most proteins are synthesized in the cell body and must be transported through thin structures over long distances where normal diffusion is insufficient. Neurons transport subcellular cargo along axons and neurites through a stochastic interplay of active and passive transport.

Measuring nonequilibrium vesicle dynamics in neurons under tension.

Vesicle transport in neurons is a highly complex nonequilibrium process. Their subcellular environment is undergoing constant fluctuations from thermal energy and molecular motors. Vesicle transport is an interplay between random motion (passive) and directed motion (active) driven by molecular motors along cytoskeletal filaments.

Myoblast morphology and organization on biochemically micro-patterned hydrogel coatings under cyclic mechanical strain.

Mechanical forces and geometric constraints play critical roles in determining cell functionality and tissue development. Novel experimental methods are essential to explore the underlying biological mechanisms of cell response. We present a versatile method to culture cells on adhesive micro-patterned substrates while applying long-term cyclic tensile strain (CTS).