Lateral migration of electrospun hydrogel nanofilaments in an oscillatory flow

<div><p>The recent progress in bioengineering has created great interest in the dynamics and manipulation of long, deformable macromolecules interacting with fluid flow. We report experimental data on the cross-flow migration, bending, and buckling of extremely deformable hydrogel nanofilaments conveyed by an oscillatory flow into a microchannel. The changes in migration velocity and filament orientation are related to the flow velocity and the filament’s initial position, deformation, and length. The observed migration dynamics of hydrogel filaments qualitatively confirms the validity of the previously developed worm-like bead-chain hydrodynamic model. The experimental data collected may help to verify the role of hydrodynamic interactions in molecular simulations of long molecular chains dynamics.</p></div

An example of U-shaped hydrogel nanofilament in the oscillatory flow, <i>d</i> = 181 nm, <i>L</i> = 32 μm, <i>V</i>_<i>max</i> = 282 μm/s, <i>U</i>_<i>r</i> <i>=</i> 10⁻³.

<p>(a)–lateral migration path of the nanofilament into the channel axis, center of mass position at each zero-crossing of the flow oscillation (n * π, n = 1,2,3.); (b)–relative longitudinal slip velocity <i>U</i>_<i>s</i> of the filament observed for each maxima of the oscillating flow (n * π/2, n = 1,3,5.). Remarkable out of phase pattern due to the filament deformations.</p

Characterization of flow field in an experimental microchannel.

<p>Schematic view of the flow configuration—(a); oscillatory flow waveform—(b); profiles of velocity- (c) and shear rate—(d) calculated for the plane of observations.</p

Selected characteristics of hydrogel nanofilaments analyzed in the present experiment compared with the bead-spring WLC model [18–20] and the experiment with polymer fibers [18].

<p><i>Sp</i>, <i>Pe</i>, <i>K</i>, <i>A</i>, <i>U</i>_<i>r</i>, <i>U</i>_<i>s</i> of hydrogel nanofilaments are reported as range of values and as mean ± standard deviation.</p

Lateral migration of <i>1</i>μ<i>m</i> spherical tracer in the oscillatory channel flow, particle position measured at zero-crossing of each oscillation period.

<p>(a)—<i>V</i>_<i>max</i> <i>= 259</i> μ<i>m/s; Re = 0</i>.<i>063; ω = 5</i>.<i>9</i>, slope of the line indicates relative migration velocity <i>U</i>_<i>r</i> <i>= 2</i>.<i>1 10</i>^<i>−3</i>; (b)—<i>V</i>_<i>max</i> <i>= 119</i> μ<i>m/s</i>, <i>Re = 0</i>.<i>046; ω = 5</i>.<i>9; U</i>_<i>r</i> <i>= 0</i>.<i>6 10</i>^<i>−3</i>.</p

Statistics of cross-stream migration.

<p>(a)—distribution of hydrogel nanofilaments across the microchannel between centerline (0) and wall (1) at initial (<i>grey bars</i>) and final (<i>dashed contour lines</i>) oscillatory cycle; (b)—relative filament slip velocity <i>Us</i> for the three groups; (c)—relative change of the inclination angle for each group of nanofilaments: final orientation (<i>dashed-patterned bars</i>) normalized to the initial orientation (<i>grey bars</i>).</p

Lateral migration for hydrogel nanofilaments.

<p>(a)—toward the channel center (<i>d = 105 nm</i>, <i>L = 41</i> μ<i>m</i>, <i>V</i>_<i>max</i> <i>= 250</i> μ<i>m/s</i>, <i>relative migration velocity U</i>_<i>r</i> <i>= 0</i>.<i>85 10</i>^<i>−3</i>; (b)—toward the wall (<i>d = 134 nm</i>, <i>L = 54</i> μ<i>m</i>, <i>V</i>_<i>max</i> <i>= 132</i> μ<i>m/s</i>, <i>U</i>_<i>r</i> <i>= 0</i>.<i>6 10</i>^<i>−3</i>.</p

Flow induced changes in nanofilament shape observed after 9–10 oscillatory cycles.

<p>Variation of degree of buckling for bent (a, b), U-shaped stretched (c, d) and U-shaped buckled (e, f) nanofilaments recorded at each forward (<i>left column</i>) and reversed (<i>right column</i>) oscillatory cycle. Solid lines indicate the data trend. (g)–changes in the end-to-end contour length distribution for the three groups of nanofilaments, at the initial oscillatory cycle (<i>grey bars</i>) and after the final cycle (<i>dashed-pattern bars</i>).</p

Histological changes in kidneys and tissue layer regeneration on ureter segments in both tested groups.

<p>RG-renal glomeruli, RT-renal tubules, E-epithelial layer, SM-smooth muscle layer. AAM – acellular aortic arch scaffold, PLCL - poly(L-lactide-<i>co</i>-caprolactone). Magnification was placed in right corner of images.</p

Integration of scaffolds with native ureters – macroscopic evaluation.

<p>A, C – lack of integration of electrospun nanofibrous scaffold; B – good integration of electrospun nanofibrous scaffold, it is impossible to find anastomosis site; D-F – good integration of aortic arch scaffold. C – conduit, U – ureter. Arrows marked sites of anastomosis.</p