Supporting Information for
Microfluidic point-of-care blood panel based on a novel
technique: reversible electroosmotic flow
M. Mohammadi, H. Madadi and J. Casals-Terré
Electroosmotic flow numerical simulation
To understand the effects of the electroosmotic flow generated by the DC electric field on the filtration
process, a 2 D model of the interface surface of two parts is built using ANSYS 14.5. Figure 1 (a) highlights
the location of this cross-section. This model is used to study the motion of the plasma under the presence of
the electric field, which asses the filling of the plasma-collected channels. In the simulated channel, a
potential difference of 50 V is applied between the inlet and the outlet to generate electroosmotic flow. The
eletroosmotic velocity is a function of the electric field, thus the electroosmotic velocity is in the same
direction of electric field.
The obtained contours and vector plots of electric field on the interface surface are shown in Figure 1s (b-d).
The electric field analysis demonstrates that the electroosmotic velocity is from positive to negative electrodes
(left to right). The results indicate that the direction of electric field in the microfilter (MIMP) is favorable to
drive the blood plasma to fill plasma collected channels.
The direct current (DC) voltage is set to 50 V to avoid hemolysis during the experiment; the human
erythrocytes (red blood cells, RBC) are lysed when an electric field exceeds 600 V/cm 18-19.The numerical
result shows the generated electric field in the channel is much less than the one that causes RBC lysis. The
electroosmotic mobility is measured experimentally by micro particle image velocimetry and its value turns
out to be 2.8 × 10−4 cm2 V −1 s −1 , which indicates that the range of electroosmotic velocity is between 60 to 80
µm/s.
Fig. S-1 Contour plot and vector plot of the electric field (V/m) at interface surface of top and bottom parts in the
microdevice (Voltage =50V), (a) Electric field contour plot of micro device (b) Electric field vector at the initial part of
MIMP (c) Electric field vector plot at the end part of MIMP
The numerical results are experimentally validated using the manufactured channels. Figure S-1 shows the
direction of EOF in the transport and MIMP channels, which agrees with the numerical simulations. The flow
direction causes the accumulation of RBCs in the entrance of the MIMP filtration. In order to break the
accumulation of RBCs and avoid clogging in the entrance of the filtration area, the direction of the electric
field is changed and therefore the EO flow direction. Figure S-2 (b) shows the backward generated
electrosmotic flow when the polarity is changed. This flow pushes the RBC away from the entrance of the
MIMP and breaks the RBC clogging. A video clip of the breaking performance of RBCs clogging is
presented in the supplementary movie S-2
Fig. S-2 RBC clogging, breakage procedure. (a) The RBCs clog the entrance of the filtration area. (b) The entrance is
opened after 5 seconds.
Separated plasma, time and purity for whole tests
The results of five fabricated devices are presented in the following table S1.
TABLE S-1. The results of five fabricated devices
Time
(Minute)
Purity
%
8
99
0.95 µL
9
99
1.2 µL
12
98
8 µL
1.1 µL
8
100
11.5 µL
1 µL
10
99
Number of tests
Blood Sample
Volume
Volume of The
Extracted Plasma
1
10µL
1 µL
2
9 µL
3
12 µL
4
5
Image analysis for red blood cells hemolysis
ImageJ software is used to analyze the quality of plasma during the experiment. The variation of the
color intensity is measured over a 160-µm line region 20 seconds and 8 minutes after the beginning of
the test in the MIMP filtration area. The same procedure is repeated for the blood sample in the
transport channel, see Figure S-3.
The measurement shows that the variation of plasma color intensity is negligible (less than 1%)
during the experiment (8 minutes) therefore the plasma is separated without hemol ysis.
Fig. S-3 The micrographs of changing color intensity during of blood plasma separation process (after 20s and 8min)