Biomedical Engineering Reference
In-Depth Information
(a)
(b)
Fig. 10.13.
(a) Two parallel channels, one with opening geometries that are the reverse of the other,
are connected to common inlet and outlet reservoirs. The height of the device is 4
.
2
μ
m, the distance
between the pillars is 3
m. (b) Snapshot from
video of labeled cells moving through the device. Liquid flow is from right to left (from [67])
μ
m, and the distance between rows of pillars is 10
μ
For the effect of temperature on the flow dynamics of the RBC we refer the
reader to [66] where the ratio of the local pressure gradient and average cell veloc-
ity (
V
) as a function of temperature is examined. The main finding is that there
exists a threshold cross-section below which the RBC viscous components begin
to play a significant role in its dynamic flow behaviour; this effect is less profound
at higher temperatures. Since the energy dissipation in the membrane is typically
higher than in the internal fluid, one might expect the influence of membrane vis-
cosity on the flow behaviour of the RBC across such small cross-sections to be large
compared to the internal fluid viscosity [71].
The second set of experiments was performed in the J. Han Lab at MIT. The mi-
crofluidic device consists of two channels, 4
Δ
P
/
m
triangular obstacles are placed into the channels as shown in Fig. 10.13(a). The dis-
tance between the obstacles is 3
.
2
μ
m in height. Rows of 3 by 10
μ
μ
m, while the distance between rows of obstacles is
10
m. The only difference between the two channels in the device is the orientation
of the obstacles; one channel is the other flipped by 180
◦
.
For low-Reynolds number flows, the resistance and average fluid velocities in the
absence of cells must be the same for both channels. When the RBC concentration
is low, the cells move with different average velocities in the two channels. This
indicates that for openings of the same minimal cross-section area, the geometry
(rate) of constriction affects the amount of force required for cell traversal. Also, the
channels appear to be sensitive to some specific properties of RBCs, therefore the
device can be used to estimate these properties for a given cell from its velocity at
known applied pressure gradient.
In simulations, the solid walls are assembled from randomly distributed DPD
particles whose positions are fixed. In addition, bounce-back reflections are used to
achieve no-slip conditions and prevent fluid particles from penetrating the walls [68].
A portion of the microfluidic device with dimensions 200 by 120 by 4.2 microns
containing 5 rows of pillars (10 pillars in each row) is modelled. The fluid region
is bounded by four walls while periodic boundary conditions are used in the flow
direction. Here, the RBC is simulated using 5,000 DPD particles to obtain accurate
results unlike most of the other simulations, including the previous example, where
μ
