Shear-induced diffusivity of a red blood cell suspension: effects of cell dynamics from tumbling to tank-treading

Hydrodynamic interactions generate a diffusive motion in particulates in a shear flow, which plays seminal roles in overall particulate rheology and its microstructure. Here we investigate the shear induced diffusion...

Tracer dynamics in crowded active-particle suspensions

Active tracers in dense suspensions show diffusive, sub-diffusive, and super-diffusive motion signalling an interplay of self-propulsion and particle interactions.

Cross-Correlations in the Brownian Motion of Colloidal Nanoparticles

"The two-body cross-correlation for the diffusive motion of colloidal nano-spheres is experimentally investigated. Polystyrene nano-spheres were used in a very low concentration suspension in order to minimize the three- or more body collective effects. Beside the generally used longitudinal and transverse component correlations we investigate also the Pearson correlation in the magnitude of the displacements. In agreement with previous studies we find that the longitudinal and transverse component correlations decay as a function of the inter-particle distance following a power-law trend with an exponent around -2. The Pearson correlation in the magnitude of the displacements decay also as a power-law with an exponent around -1. Keywords: colloidal particles, Brownian motion, cross-correlation. "

Calcium-vesicles perform active diffusion in the sea urchin embryo during larval biomineralization

ABSTRACTBiomineralization is the process by which organisms use minerals to harden their tissues and provide them with physical support. Biomineralizing cells concentrate the mineral in vesicles that they secret into a dedicated compartment where crystallization occurs. The dynamics of mineral-vesicle motion and the molecular mechanisms that regulate it, are not well understood. Sea urchin larval skeletogenesis provides an excellent platform for the analyses of vesicle kinetics. Here we used calcein labeling and lattice light-sheet microscopy to investigate the three-dimensional (3D) vesicle dynamics in control sea urchin embryos and in Vascular Endothelial Growth Factor Receptor (VEGFR) inhibited embryos, where skeletogenesis is blocked. We developed computational tools for displaying 3D-volumetric movies and for automatically quantifying vesicle dynamics in the different embryonic tissues. Our findings imply that calcium vesicles perform an active diffusion motion in all the cells of the embryo. This mode of diffusion is defined by the mechanical properties of the cells and the dynamic rearrangements of the cytoskeletal network. The diffusion coefficient is larger in the mesenchymal skeletogenic cells compared to the epithelial ectodermal cells, possibly due to the distinct mechanical properties of the two tissues. Vesicle motion is not directed toward the biomineralization compartment, but the vesicles slow down when they approach it, and probably bind for mineral deposition. Under VEGFR inhibition, vesicle volume increases and vesicle speed is reduced but the vesicles continue in their diffusive motion. Overall, our studies provide an unprecedented view of calcium vesicle 3D-dynamics and illuminate possible molecular mechanisms that control vesicle dynamics and deposition.Authors summaryBiomineralization is a widespread, fundamental process by which organisms use minerals to harden their tissues. Mineral bearing vesicles were observed in biomineralizing cells and believed to play an essential role in biomineralization, yet little is known about their three-dimensional (3D) dynamics. Here we quantify 3D-vesicle-dynamics during skeleton formation in sea urchin larvae, using lattice-light-sheet microscopy. We discover that calcium vesicles perform an active diffusive motion in both calcifying and non-calcifying cells of the embryo. The motion of the vesicles in the calcifying skeletogenic cells, is not directed toward the biomineralization compartment and has a diffusion coefficient of ~0.01μm2/sec and average speed of ~0.09μm/sec. The inhibition of Vascular Endothelial Growth Factor Receptor (VEGFR) that blocks skeletogenesis, increases vesicle volume and decreases vesicle speed but doesn’t change the diffusion mode in the embryo cells. Our studies reveal the diffusive motion of mineral bearing vesicles and have implications on basic and translational research.

Thermophoretic tweezers for single nanoparticle manipulation

We present the trapping and manipulation of a single nano-object in an aqueous medium by optically induced temporally varying temperature gradients. By real-time object tracking and control of the position of the heating laser focus, we can precisely employ thermophoretic drift to oppose the random diffusive motion. As a result, a nano-object is confined in a micrometer-sized trap. Numerical modeling gives a quantitative prediction of the effect. Traps can be dynamically created and relocated, which we demonstrate by the controlled independent manipulation of two nanoparticles.

From wavelike to sub-diffusive motion: exciton dynamics and interaction in squaraine copolymers of varying length

We measure excitation energy transport in conjugated polymers using direct observation of exciton pair dynamics.

Correction: From wavelike to sub-diffusive motion: exciton dynamics and interaction in squaraine copolymers of varying length

Correction for ‘From wavelike to sub-diffusive motion: exciton dynamics and interaction in squaraine copolymers of varying length’ by Pavel Malý et al., Chem. Sci., 2020, 11, 456–466, DOI: 10.1039/C9SC04367E.

Directional control of surface rolling molecules exploiting non-uniform heat-induced substrates

Exploiting a surface subjected to a temperature gradient to convert the diffusive motion of nanocars to guided directional motion.