Biomimetic Autoseparation of Leukocytes from Whole Blood in a Microfluidic Device

Abstract

Leukocytes comprise less than 1% of all blood cells. Enrichment of their number, starting from a sample of whole blood, is the required first step of many clinical and basic research assays. We created a microfluidic device that takes advantage of the intrinsic features of blood flow in the microcirculation, such as plasma skimming and leukocyte margination, to separate leukocytes directly from whole blood. It consists of a simple network of rectangular microchannels designed to enhance lateral migration of leukocytes and their subsequent extraction from the erythrocytedepleted region near the sidewalls. A single pass through the device produces a 34-fold enrichment of the leukocyte-to-erythrocyte ratio. It operates on microliter samples of whole blood, provides positive, continuous flow selection of leukocytes, and requires neither preliminary labeling of cells nor input of energy (except for a small pressure gradient to support the flow of blood). This effortless, efficient, and inexpensive technology can be used as a lab-on-a-chip component for initial whole blood sample preparation. Its integration into microanalytical devices that require leukocyte enrichment will enable accelerated transition of these devices into the field for point-of-care clinical testing.The rapidly expanding field of lab-on-a-chip microanalytical devices promises inexpensive, portable, miniaturized tools that could potentially revolutionize clinical and basic research analyses by dramatically reducing sample size and handling.1 -3 An important application of this technology is the analysis of leukocytes (white blood cells) or their contents, for which these cells must first be isolated from the whole blood sample. [4][5][6][7] Blood is a 45% suspension of cells (erythrocytes, platelets, leukocytes) in plasma. Erythrocytes (red blood cells) constitute the vast majority of all blood cells and are normally ∼1000 times more abundant than leukocytes. Traditionally, several milliliters of whole blood are drawn and then centrifuged in order to separate blood cells of different density. Plasma, platelets, and white and red cells can be separated by this procedure, but it is a labor-, energy-, and time-intensive process that relies on special equipment and requires trained personnel. 8, 9 Many current microanalytical devices have no integrated sample

A microfluidic device for partial cell separation and deformability assessment

“…A number of microfluidic devices have been developed to take advantage of these natural hemodynamics phenomena. Shevkoplyas et al [7] developed a microdevice to isolate WBCs from a blood sample by using the margination effect, whereas Hou et al [8] have very recently proposed a biomimetic separation device to separate normal RBCs from malaria infected RBCs. Other researchers have found several advantages to control and manipulate blood flow in microfluidic devices.…”

Deterministic hydrodynamics: Taking blood apart

“…The removed component may be harvested by periodically stopping the flow into the filter and flushing to remove the desired particles from the filter mesh. Additional microfluidic methods have also included magnetophoretic separation (7) and separation by leukocyte margination (8). Size-based filter methods have also been integrated with PCR amplification of genomic DNA from WBCs (9).…”

Design Principles for Microfluidic Biomedical Diagnostics in Space

“…The design in Figs. 3(c) and (d) ensured that all of the collisional energy among blood cells was dedicated to driving leukocytes to the walls, providing efficient locations for siphoning off cells (Shevkoplyas et al, 2005). This clever biomimetic technique operated effectively without sample dilution and with simple process control for minimal resource consumption.…”

“…While this technique could be used to introduce blood into the device, it is generally insufficient to pump fluid through a microfluidic device (with some notable exceptions .) Mechanically, the simplest way to drive flow is through a hydrodynamic pressure difference, produced by connecting the inlet and exit ports to fluid reservoirs of different heights (Shevkoplyas et al, 2005;Simonnet & Groisman, 2006). A 1-m difference in water column height between two reservoirs translates to an overall pressure drop of 10 kPa, which is sufficient to drive flow in an uncomplicated microdevice.…”