12 research outputs found
An Insight into the Temperature Field and Particle Flow Patterns in a Fluidized Bed Reactor for Nonpelletizing Polyethylene Process Using a 3D CFD-PBM Model
This
work aims at exploring the temperature and polyethylene (PE)
particle flow patterns in a pilot-plant fluidized bed reactor via
3D CFD modeling approach. A Eulerian–Eulerian model involving
ethylene polymerization kinetics is integrated with population balance
model to investigate the issues for both traditional pelletizing PE
process (TPPP) and nonpelletizing PE process (NPPP). The results show
that the regions with large temperature gradients have been observed
in top area. The revealed particle flow patterns in two cases are
analyzed using four typical flow patterns (patterns <b>a</b>–<b>d</b>) reported in literature. PE particles are
vigorously contacted and mixed along the lateral and vertical planes
of the reactor in TPPP (patterns <b>b</b>–<b>d</b>). Solid dispersion is intensely enhanced in the bed vertical direction
(pattern <b>d</b>), and the flow patterns show larger circular
flow (pattern <b>a</b>) in the radial direction under NPPP due
to the larger particle size and gas velocity
Asymmetric Migration of Human Keratinocytes under Mechanical Stretch and Cocultured Fibroblasts in a Wound Repair Model
<div><p>Keratinocyte migration during re-epithelization is crucial in wound healing under biochemical and biomechanical microenvironment. However, little is known about the underlying mechanisms whereby mechanical tension and cocultured fibroblasts or keratinocytes modulate the migration of keratinocytes or fibroblasts. Here we applied a tensile device together with a modified transwell assay to determine the lateral and transmembrane migration dynamics of human HaCaT keratinocytes or HF fibroblasts. A novel pattern of asymmetric migration was observed for keratinocytes when they were cocultured with non-contact fibroblasts, <i>i.e.</i>, the accumulative distance of HaCaT cells was significantly higher when moving away from HF cells or migrating from down to up cross the membrane than that when moving close to HF cells or when migrating from up to down, whereas HF migration was symmetric. This asymmetric migration was mainly regulated by EGF derived from fibroblasts, but not transforming growth factor α or β1 production. Mechanical stretch subjected to fibroblasts fostered keratinocyte asymmetric migration by increasing EGF secretion, while no role of mechanical stretch was found for EGF secretion by keratinocytes. These results provided a new insight into understanding the regulating mechanisms of two- or three-dimensional migration of keratinocytes or fibroblasts along or across dermis and epidermis under biomechanical microenvironment.</p></div
Inhibition of EGF in lateral (<i>A</i>) or transmembrane (<i>B</i>) migration of HaCaT cells.
<p>Data were presented as the mean ± SD of cell migration distance normalized by initial width of HaCaT cells at <i>t</i> = 0 day (<i>A</i>) or of fraction of transmigrated HaCaT cells at <i>t</i> = 36, 48 h normalized to that at <i>t</i> = 24 h in respective cases (<i>B</i>). Data at <i>t</i> = 24 h were not presented for the sake of clarity.</p
Transmigration of HF cells on collagen I-coated transwell chamber.
<p><i>Up-to-down</i> (<i>A</i>) or <i>down-to-up</i> (<i>B</i>) transmigration of monoclutured or cocultured HF cells in the absence or presence of mechanical stretch. Data are presented as the fraction of transmigrated HaCaT cells at <i>t</i> = 36, 48 h normalized to that at <i>t</i> = 24 h in respective cases.</p
Lateral migration set-up of HaCaT or HF cells cultured on collagen I-coated PDMS membrane in a tensile device.
<p>(<i>A</i>) An in-house developed tensile device by applying mechanical stretch, <i>via</i> the PDMS membrane, to the cells (<i>upper panel</i>). Also plotted was the tensile strain profile of PDMS membrane at a pre-set 20% strain along tensile direction (<i>x</i>-axis) (<i>lower panel</i>). (<i>B</i>) Schematic of monocultured (<i>upper panel</i>) or cocultured (<i>lower panel</i>) HaCaT or HF cells on the stretched membrane where the cells tend to migrate in two directions with a distance <i>L</i> or <i>L’</i> at a given time point. <i>Arrows</i> indicate the migration direction of the cells when they are monocultured (to leftward or rightward) or cocultured (to outward or inward). (<i>C</i>, <i>D</i>) Typical images of cocultured HaCaT cells at <i>t</i> = 0 (<i>C</i>) and 6 day (<i>D</i>) with the leading edge indicated as <i>white dashed lines</i> (<i>Bar</i> = 500 µm) with the <i>inserts</i> illustrating the magnified images (<i>Bar</i> = 100 µm). The <i>white strip</i> in (<i>D</i>) was used to disconnect the oversized image.</p
Lateral migration of HF cells on collagen I-coated PDMS membrane in the absence or presence of HaCaT cells and mechanical stretch.
<p>(<i>A, B</i>) Time course of normalized <i>instantaneous</i> or <i>accumulative</i> distance of monocultured (M/N) (<i>A</i>) or cocultured (C/N) (<i>B</i>) HF cells in the absence of mechanical stretch. (<i>C</i>, <i>D</i>) Time course of normalized <i>instantaneous</i> or <i>accumulative</i> distance of monocultured (M/S) (<i>C</i>) or cocultured (C/S) (<i>D</i>) HF cells in the presence of mechanical stretch. Data were collected and presented in the same way as <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0074563#pone-0074563-g002" target="_blank">Fig. 2</a>.</p
Inhibition of TGF-α (<i>A</i>) or TGF-β1 (<i>B</i>) in transmigration of HaCaT cells.
<p>Data were presented as the mean ± SD of fraction of transmigrated HaCaT cells at <i>t</i> = 36, 48 h normalized to that at <i>t</i> = 24 h in respective cases. Data at <i>t</i> = 24 h were not presented for the sake of clarity.</p
Transmigration of HaCaT cells on collagen I-coated transwell chamber.
<p>(<i>A, B</i>) <i>Up-to-down</i> (<i>A</i>) or <i>down-to-up</i> (<i>B</i>) transmigration of monoclutured or cocultured HaCaT cells in the absence of mechanical stretch. (<i>C</i>, <i>D</i>) <i>Up-to-down</i> or <i>down-to-up</i> transmigration of cocultured HaCaT cells in the absence (<i>C</i>) or presence (<i>D</i>) of mechanical stretch. Data are presented as the fraction of transmigrated HaCaT cells at <i>t</i> = 36, 48 h normalized to that at <i>t</i> = 24 h in respective cases.</p
Lateral migration of HaCaT cells on collagen I-coated PDMS membrane in the absence or presence of HF cells and mechanical stretch.
<p>(<i>A, B</i>) Time course of normalized <i>instantaneous</i> or <i>accumulative</i> distance of monocultured (M/N) (<i>A</i>) or cocultured (C/N) (<i>B</i>) HaCaT cells in the absence of mechanical stretch. (<i>C</i>, <i>D</i>) Time course of normalized <i>instantaneous</i> or <i>accumulative</i> distance of monocultured (M/S) (<i>C</i>) or cocultured (C/S) (<i>D</i>) HaCaT cells in the presence of mechanical stretch. Data were collected from at least triplets and presented as the mean±standard deviation (SD) of migration distance and then normalized by the initial width at <i>t</i> = 0 day. <i>P</i> value indicates the level of statistical significance of difference in normalized distances between leftward and rightward migration for M/N and M/S or inward and outward migration for C/N and C/S. <i>Arrows</i> indicate the different scales of the double y-axes for normalized <i>instantaneous</i> and <i>accumulative</i> distances.</p
Comparison of content of EGF secretion in the conditional medium using 2D (<i>A</i>) or 3D (<i>B</i>) assay.
<p>Data were collected from at least triplets and presented as the average optical intensity at OD 450</p