Supplementary Information for

Inertial blood plasma separation in a contraction–expansion array microchannel

Myung Gwon Lee,1Sungyoung Choi,1 Hee-Je Kim,2 Hee Kyun Lim,1,3 Joon-Ho Kim,3 Nam Huh,3and Je-Kyun Park1,a)

1 Department of Bio and Brain Engineering, Korea Advanced Institute of Science and Technology (KAIST), 291 Daehak-ro, Yuseong-gu, Daejeon 305-701, Republic of Korea

2 Department of Hematology, Catholic Blood and MarrowTransplantation Center, Seoul St. Mary's Hospital, College of Medicine, The Catholic University of Korea, 505 Banpo-dong, Seocho-gu, Seoul 137-701, Republic of Korea

3 Bio Lab., Samsung Advanced Institute of Technology (SAIT), Samsung Electronics Co. Ltd., Yongin-si, Gyeonggi-do 446-712, Republic of Korea

a) Electronic mail: (J.-K. Park); Tel: +82-42-350-4315; Fax: +82-42-350-4310.

Experimental

The contraction–expansion array (CEA) microchannel was fabricated in poly(dimethylsiloxane) (PDMS) using soft lithography techniques. A mixture of PDMS prepolymer and its curing agent (Sylgard 184; Dow Corning, MI) in the ratio of 9:1 was poured on the SU-8 photoresist molds and cured for 3 h in a convection oven at 65 °C. Irreversible bonding was made between a PDMS replica and a glass slide, treating both of them with oxygen plasma (200 mTorr, 200 W).

Particle migration was observed through a fluorescence microscope (TS100; Nikon Co., Japan) equipped with a charge-coupled device (DS-2MBWc; Nikon Co.) by measuring the fluorescent intensity of the fluorescent dye, 4 and 10 μm diameter polystyrene particles, corresponding model to blood plasma, red blood cells (RBCs) and white blood cells (WBCs), respectively. And, the blood plasma separation was demonstrated with human whole blood as a particle fluid; and phosphate buffered saline (PBS; Invitrogen Corporation, CA) as a focusing fluid. The hematocrit level of whole blood is ~45% which is prepared by adding the RBCs in the blood plasma. The blood plasma was mixed with fluorescein isothiocyanate (FITC)-dextran (Sigma–Aldrich Co., St. Louis, MO) for visualization at a concentration of ~250 μg/mL. The RBC samples were obtained from the Republic of Korea National Red Cross Organization (Daejeon, Korea) in compliance with safety regulations. Before each experiment, the RBCs and blood plasma samples were stored at approximately 4°C to prevent denaturation.

FIG. S1.Fluorescent microscope images of inertial migration of the 4 and 10 μm fluorescent polystyrene particles (red), and fluorescent dye (green) at an aspect ratio (AR) of 0.4 and 1 in the contraction–expansion array (CEA) microchannel. All images were captured in the expansion region after the sixth contraction region at Reynolds number (Re) of 12.5 (s1: sidewall 1, s2: sidewall 2).

Ratio of inertial force

For a modulation of the force balance between the inertial lift and Dean drag forces, the hydraulic diameter is an important factor due to the change of channel height at the same condition of Reynolds number (Re). The particle (with a diameter of ap) focusing by influence of dominant inertial lift force is strongly dependent on the ratio of inertial force (ap/Dh). We designed three types of CEA microchannel where the channel height is various with 20, 35 and 50 μm; and introduced 4, 10 and 15 μm particles into them; and quantitatively explored the effect of the inertial force on particle focusing behavior (Fig. S2). From the above analysis, for the ratio of inertial force (ap/Dh) over threshold value (~0.1), the particles start to focus as inertial lift force (FL)prevails over Dean drag force (FD). The ap/Dh of 4 μm particles at an aspect ratio (AR) of 0.4 and 1 were calculated with 0.11 and 0.05, respectively. According to Fig. S2, we can expect that the RBC separation from blood plasma is accomplished at the CEA device with 20 μm height in the regime above Re of 12.

FIG. S2.Ratio of inertial force which represents particle (with a diameter of ap) focusing by force balance between inertial lift force (FL) and Dean drag force (FD). The open circle (○) indicates if 80% intensity-width of measured single streak is less than 2ap, the open triangle (Δ) indicates if less than 10ap, and the solid rectangular (■) indicates if over 10ap. Three regimes can be distinguished: (1) FLdominant domain (FLFD) where the particles remained focused, (2) intermediate domain (FL≥FD) where most of the particles remained intermediatefocused by strong inertial lift force and weak Dean flow. (3) FD dominant domain (FLFD) where the particles entrain in Dean flow. A minimum ap/Dh 0.1 is required for focusing.

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