www.isac-net.org December 2016 | Volume 89A | Issue 12 A microfluidic blood cell sorting platform Tw o lasers are better than one: mtROS story Editor’s travel notes from China ISSN 1552–4922 Editor’s Choice Automated Leukocyte Processing by Microfluidic Deterministic Lateral Displacement Curt I. Civin,1 Tony Ward,2* Alison M. Skelley,2 Khushroo Gandhi,2 Zendra Peilun Lee,2 Christopher R. Dosier,2 Joseph L. D’Silva,4 Yu Chen,4 MinJung Kim,1 James Moynihan,1 Xiaochun Chen,1 Lee Aurich,2 Sergei Gulnik,3 George C. Brittain,3 Diether J. Recktenwald,6 Robert H. Austin,5 James C. Sturm4 Abstract 1Departments of Pediatrics and We previously developed a Deterministic Lateral Displacement (DLD) microfluidic Physiology, Center for Stem Cell Biology method in silicon to separate cells of various sizes from blood (Davis et al., Proc Natl and Regenerative Medicine and Acad Sci 2006;103:14779-14784; Huang et al., Science 2004;304:987-990). Here, we pre- Greenebaum Cancer Center, University sent the reduction-to-practice of this technology with a commercially produced, high of Maryland School of Medicine, precision plastic microfluidic chip-based device designed for automated preparation of Baltimore, Maryland 21201 human leukocytes (white blood cells; WBCs) for flow cytometry, without centrifuga- 2GPB Scientific LLC, Richmond, Virginia tion or manual handling of samples. After a human blood sample was incubated with 23219 fluorochrome-conjugated monoclonal antibodies (mAbs), the mixture was input to a DLD microfluidic chip (microchip) where it was driven through a micropost array 3 Beckman Coulter Life Sciences, Miami designed to deflect WBCs via DLD on the basis of cell size from the Input flow stream Florida, 33196 into a buffer stream, thus separating WBCs and any larger cells from smaller cells and 4Department of Electrical Engineering, particles and washing them simultaneously. We developed a microfluidic cell processing Princeton Institute for the Science and protocol that recovered 88% (average) of input WBCs and removed 99.985% (average) Technology of Materials, Princeton of Input erythrocytes (red blood cells) and >99% of unbound mAb in 18 min (aver- University, Princeton, New Jersey 08544 age). Flow cytometric evaluation of the microchip Product, with no further processing, lysis or centrifugation, revealed excellent forward and side light scattering and fluores- 5Department of Physics, Princeton cence characteristics of immunolabeled WBCs. These results indicate that cost-effective Institute for the Science and Technology plastic DLD microchips can speed and automate leukocyte processing for high quality of Materials, Princeton University, flow cytometry analysis, and suggest their utility for multiple other research and clinical Princeton, New Jersey 08544 applications involving enrichment or depletion of common or rare cell types from 6 Desatoya LLC, Reno, Nevada 89507 blood or tissue samples. VC 2016 International Society for Advancement of Cytometry Key terms Grant sponsor: National Foundation for Cancer Research; National Institutes of microfluidic; cell processing; white blood cells; leukocytes; blood; red blood cells; deter- Health, Grant number: R42CA174121. ministic lateral displacement; sample preparation; cell sorting Additional Supporting Information may be found in the online version of this article. AS multiparameter flow cytometry becomes increasingly more valuable and widely *Correspondence to: Tony Ward, used in research and clinical diagnostic testing for many diseases (1–8), the need for President, GPB Rare Cell Division, GPB new methods to improve the efficiency of sample preparation becomes increasingly Scientific LLC, 800 East Leigh St., #51, critical. Currently, cell membrane and intracellular labeling of cells for multiparame- Richmond, VA 23219,USA. E-mail: [email protected] ter flow cytometry is a labor- and time-intensive process that involves substantial cell losses, especially using protocols that require samples to be washed multiple times by centrifugation to maximize analytic quality (9). Since each cell wash step may result in a loss of 10–15% of the cells (10,11), multiple cell washes during processing for flow cytometry are not only time-consuming, requiring 30 min or more, but also obligate significant overall cell loss and sometimes preferential loss of specific cell types (12). Cell losses during processing necessitate larger starting sample volumes, an especially critical problem in clinical testing of small children and patients who need many blood tests (13–15) and in laboratory research experiments where sam- Cytometry Part A 89A: 1073 1083, 2016 À Editor’s Choice Contribution: AMS, TW, ZPL, CRD, KG, LA, MJK, GCB, SG, YC, JLD, Published online 22 November 2016 in Wiley Online Library XC, JCS, and CIC conceived and designed experiments; ZPL, CRD, (wileyonlinelibrary.com) MJK, YC, JLD, GCB, XC, and JM performed experiments; AMS, ZPL, DOI: 10.1002/cyto.a.23019 CRD, provided reagents and materials; AMS, TW, ZPL, CRD, KG, MJK, GCB, and CIC analyzed and interpreted results; CIC, JCS, TW, AMS, VC 2016 International Society for Advancement of Cytometry KG, LA, GCB, and SG wrote the article. ples are often unique or of limited volume, such as in small Microchip Fabrication animal studies. In addition, the manual nature of these steps A silicon master for the plastic DLD microchip was made may lead to significant intraoperator and interoperator vari- using standard photolithographic and deep reactive ion etch- ability. Finally, improved, automated methods of sample prep- ing techniques (21) (A. M. Fitzgerald, Burlingame, CA). The aration would be valuable for multiple types of analysis silicon master was then transferred to a soft elastomeric mold beyond flow cytometry, such as genetic and genomic testing, (Edge Embossing, Medford, MA). The elastomer was peeled off and thus several approaches to take advantage of microfluidic to create a negative imprint of the silicon master; this soft elasto- processes for cell sample preparation have been reported meric mold was then used to emboss 100 plastic chips as fol- (16–18). lows: using a combination of pressure and temperature, the Our previous research using silicon devices produced in plastic was extruded into the features (wells) of the soft- small numbers in our research laboratories has shown that elastomer negative mold, replicating the features and depth of Deterministic Lateral Displacement (DLD) microfluidic chip the original silicon master. The soft tool was then peeled off from (microchip)-processing technology harvests cells from a flow the plastic device, producing a flat piece of plastic surface- of fluid purely on the basis of cell size (19,20). The DLD embossed to a depth of 60 mm with a pattern of flow channels approach involves pumping blood through a microfluidic and trenches around an array of microposts (Fig. 1C). Ports were device containing a specifically designed array of microposts created for fluidic access to the Input and Output ends of the that is tilted at a small angle from the direction of the fluid microchip. After batch cleaning by sonication, the devices were flow. Cells larger than the target size of the micropost array batch lidded with a heat-sensitive, hydrophilic adhesive (ARFlow were gently deflected (“bumped”) by the microposts into a Adhesives Research, Glen Rock, PA). stream of buffer, a process that was non-injurious to the cells. Microchip Operation This study presents the reduction-to-practice of this approach The microfluidic device was assembled inside a mani- for clinical applications requiring inexpensive, commercially fold with fluidic connections. Fluids were driven through the manufactured, high precision, disposable plastic DLD micro- DLD microchip using pneumatic pressure (MFCS-EZ, Flui- chips. These DLD microchips provided rapid (<20 min), gent, Lowell, MA). The flow path for the buffer line included automatable, noncentrifugal washing of leukocytes (white an in-line degasser (Biotech DEGASi, Minneapolis, MN). blood cells; WBCs) together with depletion of erythrocytes The microchip was first primed at low pressure with run 21 21 (red blood cells; RBCs) and unbound monoclonal antibodies buffer [Ca -andMg -free phosphate buffered saline (mAbs) from small samples of unprocessed human blood, (PBS), Mediatech, Manassas, VA] containing 5 mMEDTA with high viability and recovery of all of the major WBC sub- (Sigma Aldrich, St. Louis, MO) and either 1% bovine serum sets for high-quality flow cytometry analyses. albumin (BSA; MP Biomedicals, Santa Ana, CA) or 1% poloxamer (Kolliphor P-188, Sigma Aldrich), as noted. The system was then brought to standard operating pressure and flushed with run buffer for 15 min. The system was depres- MATERIALS AND METHODS surized, and the sample loaded into the sample Input port. The sample and buffer Input containers were repressurized Microchip Design to drive samples through the microchip, and the Product In the single channel plastic microchip used in this study, and Waste were collected at their Output ports. After the the DLD array consisted of three subarrays of increasingly complete sample volume was processed (<20 min), either an smaller posts and gaps, and thus critical sizes (Fig. 1A). The air plug or additional buffer was used to flush the chip, as cells first enter zone 1 containing 24 m-diameter posts sepa- m noted. The Product Output volume was similar to the Sam- rated by 18 mm gaps ( 8 mm critical diameter), followed by ple Input volume.