Serious diseases such as diabetes and malaria are deeply related to microcirculation
disorders caused by abnormal erythrocytes deformability [1]. Therefore, various studies on
red blood cells (RBCs) deformation have been carried out but those studies rather focus
on shear
ow or extensional
ow [2-6]. In this study, a relatively low aspect ratio (AR)
hyperbolic microchannel was used in order to create an extensional
ow combined with a
shear
ow, where AR=
h
w
, h means the depth and w means the width of the microchannel.
The objective of the study is to investigate the degree of RBC deformation throughout
the microchannel at the centerline (y = 0). The blood samples were RBCs diluted with
the Hank's Balanced Salt Solution (HBSS) with the hematocrit (Hct) level set to be 2%.
A polydimethylsiloxane (PDMS) microchannel, having a hyperbolic contraction region
followed by an abrupt expansion shape, was fabricated by a soft-lithography technique.
The dimensions of the microchannel: width of the inlet (w), length of contraction region
(l), width of the exit of contraction (wc) and depth (h) were 400 m, 580 m, 20 m and 14 m, respectively. Hence, the AR was 0:035. The experimental equipment consisted
of an inverted microscope (Diaphot 300, Nikon), a high-speed camera (FASTCAM SA3,
Photron) connected to a computer and a 1mL syringe (TERUMO R
SYRING) controlled
by a syringe pump (PHD ULTRA). The manufactured PDMS microchannel was placed on
the stage of the microscope where the
ow rate Q of the working
uids was kept constant
at 0:5 L=min. The
owing RBCs were recorded by a high speed camera at a frame rate
of 7500 frames/s and analyzed. The DI was obtained by DI=
a b
a + b
where a refers to
the major axis and b refers to the minor axis of the ellipse best tted to RBCs. High
DI values in the contraction region were observed. It is possible to say that the RBCs
highly elongate with both extensional and shear dominated
ows achieved by a hyperbolic
microchannel with a relatively low aspect ratio AR
