Confocal Micro-PIV/PTV Measurements of the Blood Flow in Micro-channels - Bioanalysis Advanced Materials Methods and Devices - page 136

0.15 0.20 0.26 0.32 0.37 0.42 0.48 mm/s

0.45

0.4
0.35
0.3
0.25
300

0.45
0.4
0.35
0.3
0.25
300

0

0

50

50

200

100

U

100

100

150 200

Y
X

150

100

200 0

200 0

Fig. 9.7 Ensemble velocity profiles with PS ( left image ) and in vitro blood 20 %Hct ( right imag e)
in a rectangular PDMS micro-channel (from [ 27 ])

shear rate in the vicinity of the wall, Hct temporal variation and the light scattered
and absorbed from the RBCs.
Lima and his colleagues have performed another study to measure both ensem-
ble and instantaneous velocity profiles for in vitro blood (Hct up to 17%) flowing
through a 100-

m square micro-channel [ 25 ]. All the measurements were made in
the middle plane at a constant flow rate and low Reynolds number ( Re

m

0.025).
Although the ensemble velocity profiles were markedly parabolic, some
fluctuations in the instantaneous velocity profiles were found to be closely related
to the Hct increase. This study has also shown strong evidence that the Root Mean
Square (RMS) increases with the Hct increase suggesting that the concentration of
RBCs within the plasma flow strongly influences the measurements of the instanta-
neous velocity fields. Possible reasons for the RMS increase are the motion and
interaction of RBCs and the light scattered and absorbed by the RBCs. This latter
behaviour seems to be predominant at an Hct value of about 17%. More detailed
information about these results can be found in Lima et al. [ 25 ].

¼

9.4.3 Confocal Micro-PTV Results

Confocal micro-PIV experiments have shown the ability to measure with good
accuracy in vitro blood with Hct up to 9%, in a 100-

m square micro-channel.
However, for Hct bigger than 9%, the light absorbed by the RBCs contributes to
diminishing the concentration of tracer particles in the recorded confocal images.
The low density images become more evident for Hct bigger than 20%, which
generates spurious errors in the velocity fields [ 25 ]. Therefore, Lima and his
colleagues [ 24 , 26 , 28 ] have applied a new approach, known as confocal micro-
PTV, to track the trajectories of individual labelled RBCs at high Hcts. Figures 9.8
and 9.9 show the ability of this confocal method to measure the motion of blood
cells at both diluted (3% Hct) and high (20% Hct) suspensions of RBCs, respec-
tively. Additionally, successful measurements were performed in a 75-

m

m m circular

PDMS micro-channel as shown in Fig. 9.10 .