A mechanochemical model of cell reorientation on substrates under cyclic stretch.

We report a theoretical study on the cyclic stretch-induced reorientation of spindle-shaped cells. Specifically, by taking into account the evolution of sub-cellular structures like the contractile stress fibers and adhesive receptor-ligand clusters, we develop a mechanochemical model to describe the dynamics of cell realignment in response to cyclically stretched substrates. Our main hypothesis is that cells tend to orient in the direction where the formation of stress fibers is energetically most favorable. We show that, when subjected to cyclic stretch, the final alignment of cells reflects the competition between the elevated force within stress fibers that accelerates their disassembly and the disruption of cell-substrate adhesion as well, and an effectively increased substrate rigidity that promotes more stable focal adhesions. Our model predictions are consistent with various observations like the substrate rigidity dependent formation of stable adhesions and the stretching frequency, as well as stretching amplitude, dependence of cell realignment. This theory also provides a simple explanation on the regulation of protein Rho in the formation of stretch-induced stress fibers in cells

Influence of pressure and temperature on the toluene desorption from activated carbon under supercritical CO2

Desorption of activated carbon saturated with VOCs (volatile organic compounds) under supercritical CO2 is greatly affected by pressure and temperature, and the influence mechanism remains ambiguous. In this paper, toluene is considered as the representative of VOC, influence of pressure and temperature on the toluene desorption ratio is investigated by experimental and molecular dynamic simulation methods. The experimental results show that the toluene desorption ratio increases as pressure increases, but the influence of temperature on the toluene desorption ratio is affected by pressure. The desorption ratio decreases with increasing temperature at lower pressure, while the desorption ratio increases at the beginning but then decreases with increasing temperature at higher pressure. The mechanism analysis presents that the influence of pressure is governed by “density effect”, the influence of temperature is governed by “density effect” and “diffusion effect” together, the final result is determined by the competition between the two effects

Reorientation of multiple cells on cyclically stretched substrates.

<p>(a) Alignment of 100 individual cells adhered to a substrate which is subjected to a 10% stretch at 1 Hz. The stretch is applied along the horizontal direction and from left to right, the order parameters corresponding to particular time points are: , and . (b, c) Dynamic evolution of the order parameter representing instantaneous cell orientation of 100 cells on the cyclically stretched substrate at different values of straining frequency, amplitude and rotational diffusivity. Each error bar reflects the standard deviation (SD) of 10 independent sets of simulation.</p

Long-time average filament density as a function of the cell orientation angle under different values of stretching amplitude (stretch frequency: 1 Hz).

<p>Long-time average filament density as a function of the cell orientation angle under different values of stretching amplitude (stretch frequency: 1 Hz).</p

Effects of Poisson's ratio on cell reorientation.

<p>(a) The effective stretching strain acting on each SF as a function of cell orientation angle , influenced by Poisson's ratio of substrate materials. (b, c, d) Long-time average filament density as a function of the cell orientation angle for slow kinetic process () and (b) , (c) and (d) without strain stiffening effects, respectively.</p

The compliance of the bond-substrate system represented by the effective spring constant <i>K</i>.

<p>The receptors actually bind to specific head groups of certain adhesion molecules, such as fibronectin, coated on the substrate surface.</p

Evolutions of the bond and filament densities.

<p>(a) A relatively stiff substrate of . (b) A relatively soft substrate of .</p

Multigene phylogeny and morphology reveal Ophiocordyceps hydrangea sp. nov. and Ophiocordyceps bidoupensis sp. nov. (Ophiocordycipitaceae)

Ophiocordyceps species have a wide range of insect hosts, from solitary beetle larva to social insects. However, among the species of Ophiocordyceps, only a few attack cicada nymphs. These species are mainly clustered in the Ophiocordyceps sobolifera clade in Ophiocordyceps. A new entomopathogenic fungus parasitic on cicada nymphs, and another fungus parasitic on the larva of Coleoptera, are described in this study. The two new species viz. Ophiocordyceps hydrangea and Ophiocordyceps bidoupensis were introduced based on morphology and multigene phylogenetic evidence. The phylogenetic framework of Ophiocordyceps was reconstructed using a multigene (nrSSU, nr LSU, tef-1α, rpb1, and rpb2) dataset. The phylogenetic analyses results showed that O. hydrangea and O. bidoupensis were statistically well-supported in the O. sobolifera clade, forming two separate subclades from other species of Ophiocordyceps. The distinctiveness of these two new species was strongly supported by both molecular phylogeny and morphology

Long-time average filament density

<p><b> in “Rho-inhibited” cells (</b><b>) as a function of the orientation angle </b><b> under a 10% stretch at 1 Hz.</b> The results clearly show the difference between the cases with and without strain stiffening effects.</p