Biomedical Engineering Reference
In-Depth Information
2.5
w = 3 μ m − Exp
w = 4
m − Exp
w = 5 μ m − Exp
w = 6 μ m − Exp
w = 3
μ
20
Experiment
Model
2
m − DPD
w = 4 μ m − DPD
w = 5
μ
1.5
15
m − DPD
w = 6 μ m − DPD
μ
1
10
0.5
5
0
3
6
4
5
0
0.05
0.1
0.15
0.2
Channel Width (
m)
Local
Δ
P (kPa)
(a)
μ
(b)
Fig. 10.12. Quantitative flow behaviour of RBC traversal of microfluidic channels. (a) Measured
and simulated cell lengths at the center of the microfluidic channel for varying channel widths.
(b) Comparison of DPD simulation results (open markers) with experimentally measured mean
velocities (filled markers) of RBC traversal as a function of measured local pressure differences
for3,4,5and6 o μm channel widths (height = 2 . 7μm, length = 30μm). Error bars on experimental
data points represent an average
+ /−
one standard deviation of a minimum of 18 cells. Error bars
on modelling data points indicate minimum and maximum variations resulting from a case study
exploring the sensitivity of the RBC traversal to channel geometry and cell volume (from [66])
viscosity at 22 C, while the membrane viscosity is decreased by 50 % and 63.5 %,
respectively, to match the experimentally measured RBC relaxation times at these
temperatures.
Fig. 10.11(b) presents a qualitative comparison of experiment with the DPD
model for RBC traversal across a 4
m wide channel. Here, the cell undergoes a
severe shape transition from its normal biconcave shape to an ellipsoidal shape with
a longitudinal axis up to 200 % of the average undeformed diameter. Fig. 10.12(a)
illustrates how the longitudinal axis of the cell, measured at the center of the chan-
nel, changes with different channel widths. Experimental and simulated longitudinal
RBC axes typically differ no more than 10-15 %. Fig. 10.12(b) presents pressure-
velocity relationships for RBC flow across channels of different cross-sectional di-
mensions. Average cell velocity measurements were taken between the point just
prior to the channel entrance (the first frame in Fig. 10.11(b)) and the point at which
the cell exits the channel (the final frame in Fig. 10.11(b)). The DPD model ade-
quately captures the scaling of flow velocity with average pressure difference for
4-6
μ
m
wide channels can be attributed largely to variations in cell size and small varia-
tions in channel geometry introduced during their microfabrication. For the smallest
channel width of 3
μ
m wide channels. The significant overlap in the experimental data for 5-6
μ
m, the experimentally measured velocities are as much as half
those predicted by the model. This may be attributed to several factors, including
non-specific adhesive interactions between the cell membrane and the channel wall
due to increased contact. Furthermore, this 3
μ
m 2 ) cross-section
μ
m
×
2.7
μ
m(8
.
1
μ
m 2 ) limit for RBC transit of ax-
isymmetric pores [70]. Therefore, very small variations in channel height (due, for
example, to channel swelling/shrinking due to small variations in temperature and
humidity) can have significant effects.
approaches the theoretical 2
.
8
μ
m diameter (6
.
16
μ
 
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