Controlling chain flexibility in collagen networks to produce hydrogels with distinct properties

<p>The structure, mechanical properties, and optical density of gels prepared from collagen in a manner that induces the dynamical arrest of the constituent polymers before substantial fibrillogenesis can take place have been investigated. Small angle X-ray scattering and confocal laser scanning fluorescence microscopy reveal that these gels exhibit substantially different network structures, over length scales ranging from a few nanometers to many microns, when compared with traditional collagen networks in which fibrillogenesis is intentionally induced. The highly associated arrangements of the more flexible structural components found in the arrested network yield a considerably lower optical density and higher viscoelastic storage modulus when compared to a “conventional” collagen gel; while the small amount of fibrils that do manage to form still yield strain stiffening and account for the fact that at high strains, moduli from both systems fall onto the same master curve.</p

Method for determining the total displacement of villus tips (TD).

<p>A) A spatiotemporal intensity (ST) map taken along an LOI (indicated by the dashed line in (B) situated 20 µm below the villus tip before flow commenced (left arrow on upper border of map) and at the time of maximum displacement (TD) (right arrow on upper border of map). B) Views of the villus from which the ST map was taken before flow commenced and at the time of maximum displacement (right). The square marks a distinctive structural feature used as a reference point. The value of TD is calculated from the difference in the location of the same distinctive feature in the two images.</p

Variation of U_x with lengthwise distance from the villous tip.

<p>Flow velocity component at right angles to the long axis of the villi (U_x) were determined 30 µm lateral to the villous image edge at three perfusion flow rates – A) 3.8 mL/min, B) 7.6 mL/min, C) 15.3 mL/min. Zero on both Y axes corresponds to tip of the villus while negative distances are distances below the villous tip. Exponential fits (R² given on each plot) were obtained for all three perfusion rates. The different symbols on each plot represent a different experimental runs on different villi.</p

Relationship between displacement of points along the villous length with distance from the villous tip.

<p>The plot utilized data pooled from all villi*. Displacement is expressed as a percentage of total tip displacement (TD). The regression lines that best fitted the data obtained at each perfusion rate were all linear. * R² values shown are for pooled data. R² values for SLRs of individual villi were all above 0.8 at each flow rate. The dotted lines are 95% confidence intervals.</p

Variation of TD with volumetric flow rate.

<p>A box plot showing the variation of TD with perfusion flow rate is presented. There was no significant variation of TD with flow on ANOVA of logarithmically transformed data.</p

Relationship between local velocity of microbeads and the volumetric perfusion rate.

<p>The local velocity of microbeads were taken in the region 200 µm above the villous tips and determined by mPIV. Physiological flow rates reported during the postprandial period <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0100140#pone.0100140-Bueno1" target="_blank">[20]</a>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0100140#pone.0100140-Grovum1" target="_blank">[21]</a> are indicated by the shaded region in the plot.</p

Tissue flow cell used in experimental work.

<p>A) Lateral view, B) plan view.</p