An experimental investigation of interfacial instability in separated blood

Abstract

Experiments are done with separated human blood decelerated at constant rates to determine the maximum deceleration rate while avoiding remixing of the layers, which have different densities and viscosities. The deceleration rate affects both the stability and separation of particles through sedimentation. The velocity at onset of instability for a constant deceleration rate is experimentally determined for a 12‐cm‐diameter disk. Parameters of cell pack thickness, plasma thickness, and total thickness are investigated experimentally, and the only statistically significant parameter to affect stability is rate of deceleration. The data describe a correlation separating regions of stability and instability. To understand stability in decelerating flow of separated blood plasma and cells, the equations of motion are solved for a two‐layer fluid flow with a moving boundary and free surface. Inclusion of non‐Newtonian rheology of blood predicts large discontinuities in the shear rate, which is proposed as the cause of the interfacial instabilities. © 2019 American Institute of Chemical Engineers AIChE J, 65: 1376–1386, 2019

Factors affecting sedimentational separation of bacteria from blood

“…If the disk were decelerated too quickly, the clear plasma would mix with the adjacent cellpack layer, displaying a uniform orange hue, from yellow-orange to red, depending upon how much remixing occurred. Remixing is a manifestation of Kelvin-Helmholtz instability and is reported elsewhere 32.…”

“…32 The plasma was collected by pipette, weighed, and the volume calculated assuming plasma density of 1.024 g/ml. 32 The plasma was collected by pipette, weighed, and the volume calculated assuming plasma density of 1.024 g/ml.…”

“…26 The programmable and precision control of spinning was done using LabView software and a Maxon motor (model 301039) as described previously. 32…”

“…Finally the disk was carefully slowed, following a deceleration velocity profile that was determined through experimentation to avoid mixing of the clear plasma and the cell-pack. 32 If deceleration was too fast, the plasma and blood cells remixed, and the plasma was no longer transparent amber color. Even upon slow careful deceleration, sometimes there was a small streak of red cells in the transparent plasma.…”

Effect of dilution on sedimentational separation of bacteria from blood

“…[19][20][21] In our disk, centrifugal force pushes whole blood components toward an outer disk wall and leaves bacteria suspended in the supernatant plasma. Our current technology using a 12-cm-diameter disk can separate the RBCs from 7 ml of whole blood containing bacteria in about 20 s of spinning at 3,000 rpm, followed by 2 min of careful deceleration 22 during which time the red and white cells at the back wall slump down into a capture trough, and the bacteria-laden plasma flows into a collection space and is collected by hand pipet. 21 We achieve about 69% recovery of the original bacteria in blood, at blood concentrations down to 6 CFU/ml.…”