Biomedical subjects

Pramod A Pullarkat

Publications and source records attributed to Pramod A Pullarkat.

3 recordsLinked to original sources

PubMed2006

Self-propulsion of nematic drops: novel phase separation dynamics in impurity-doped nematogens.

We report a novel phase separation dynamics, mediated by self-propelled motion of the nucleated drops, in a mixture of a nematogen and an isotropic dopant. We show that surface flow, induced by the gradient in the concentration of the dopant expelled by the growing drops, provides the driving force for the propulsion of nematic droplets. While the liquid crystal-isotropic transition is used here to demonstrate the phenomenon, self-propulsion should be observable in many other systems in which the dynamics of a conserved order parameter is coupled to a nonconserved order parameter.

Journal Article↗

PubMed2006

A master relation defines the nonlinear viscoelasticity of single fibroblasts.

Cell mechanical functions such as locomotion, contraction, and division are controlled by the cytoskeleton, a dynamic biopolymer network whose mechanical properties remain poorly understood. We perform single-cell uniaxial stretching experiments on 3T3 fibroblasts. By superimposing small amplitude oscillations on a mechanically prestressed cell, we find a transition from linear viscoelastic behavior to power law stress stiffening. Data from different cells over several stress decades can be uniquely scaled to obtain a master relation between the viscoelastic moduli and the average force. Remarkably, this relation holds independently of deformation history, adhesion biochemistry, and intensity of active contraction. In particular, it is irrelevant whether force is actively generated by the cell or externally imposed by stretching. We propose that the master relation reflects the mechanical behavior of the force-bearing actin cytoskeleton, in agreement with stress stiffening known from semiflexible filament networks.

3T3 Cells↗

PubMed2006

Osmotically driven shape transformations in axons.

We report a cylindrical-peristaltic shape transformation in axons exposed to a controlled osmotic perturbation. The peristaltic shape relaxes and the axon recovers its original geometry within minutes. We show that the shape instability depends critically on the swelling rate and that volume and membrane area regulation are responsible for the shape relaxation. We propose that volume regulation occurs via leakage of ions driven by elastic pressure, and analyze the peristaltic shape dynamics taking into account the internal structure of the axon. The results obtained provide a framework for understanding peristaltic shape dynamics in nerve fibers occurring in vivo.

Animals↗