Biomedical Engineering Reference
In-Depth Information
polydimensiloxane (PDMS) micro-channels with complex geometries such as stenoses,
bifurcations, confluences and hyperbolic contractions [ 11 , 20 - 22 , 27 , 34 - 36 , 52 , 53 ].
Additionally, by using a wire casting technique [ 29 ] it was possible to fabricate 75-
m
m circular PDMS micro-channels.
Generally both confocal systems used in our flow studies consisted of an
inverted microscope (IX71; Olympus, Tokyo, Japan) combined with a confocal
scanning unit (CSU22; Yokogawa, Tokyo, Japan), a diode-pumped solid state
(DPSS) laser (Laser Quantum Ltd., Stockport, UK) and a high-speed camera
(Phantom v7.1;Vision Research, NJ, USA) (as in Fig. 9.5 ). All the micro-channels
were placed on the stage of the microscope where the flow rate of the working fluid
was kept constant using a syringe pump (KD Scientific Inc., Holliston, MA, USA).
A thermo-plate controller (Tokai Hit, Shizuoka, Japan) was also used: this achieved
a surrounding temperature around the micro-channel of about 37 C. More detailed
information about this system can be found elsewhere [ 23 , 24 , 27 , 28 ].
All the measurements were digitised and transferred to a computer for evaluation
using Phantom camera control software (PH607). The PIV images of the flowing
particles were processed and the flow velocity was determined using the cross-
correlation PIV method (PivView). A full description and evaluation of the confo-
cal micro-PIV system used in our studies can be found in Lima et al. [ 23 ]. For the
case of the confocal micro-PTV measurements, series of confocal images were
evaluated in Image J [ 3 ] using the manual tracking MtrackJ [ 38 ] plug-in. Generally,
the motions of the labelled RBCs were manually tracked through successive images
using the bright centroid criteria available at the MtrackJ. Using this method, it was
possible to track labelled RBCs even when two cells were in close proximity. After
obtaining a series of x and y positions, data were exported for the determination of
several physical quantities such as velocity, radial displacement, and dispersion
coefficient.
9.4.2 Confocal Micro-PIV Results
The ability of a confocal micro-PIV system to measure both pure water and diluted
suspensions of RBCs was demonstrated by Lima et al. [ 23 ]. This study was
performed with a square glass micro-channel and it was found that there was
good agreement between the measured velocity profiles of pure water and an
established analytical solution. Further work was performed by Lima et al. this
time to measure both physiological saline (PS) and in vitro blood (20% Hct) in a
rectangular PDMS micro-channel [ 27 ]. As expected for a long rectangular micro-
channel, the velocity profiles were markedly smooth and flat in the centre of the
micro-channel (as in Fig. 9.7 ). However, for the in vitro blood with 20% Hct, small
fluctuations in the shape of the ensemble velocity profiles were observed (see
Fig. 9.7 ). Possible reasons for these fluctuations are the interactions between
neighbouring RBCs, the formation of a cell-free layer, abrupt increase in the
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