A microfluidic device for continuous, real time blood plasma separation Sung Yang,* a Akif U ¨ ndar b and Jeffrey D. Zahn c Received 18th November 2005, Accepted 5th April 2006 First published as an Advance Article on the web 19th April 2006 DOI: 10.1039/b516401j A microfluidic device for continuous, real time blood plasma separation is introduced. The principle of the blood plasma separation from blood cells is supported by the Zweifach–Fung effect and was experimentally demonstrated using simple microchannels. The blood plasma separation device is composed of a blood inlet, a bifurcating region which leads to a purified plasma outlet, and a concentrated blood cell outlet. It was designed to separate blood plasma from an initial blood sample of up to 45% inlet hematocrit (volume percentage of cells). The microfluidic network was designed using an analogous electrical circuit, as well as analytical and numerical studies. The functionality of this device was demonstrated using defibrinated sheep blood. During 30 minutes of continuous blood infusion through the device, all the erythrocytes (red blood cells) traveled through the device toward the concentrated blood outlet while only the plasma was separated at the bifurcating regions and flowed towards the plasma outlet. The device has been operated continuously without any clogging or hemolysis of cells. The experimentally determined plasma selectivity with respect to blood hematocrit level was almost 100% regardless of the inlet hematocrit. The total plasma separation volume percent varied from 15% to 25% with increasing inlet hematocrit. Due to the device’s simple structure and control mechanism, this microdevice is expected to be used for highly efficient continuous, real time cell-free blood plasma separation from blood samples for use in lab on a chip applications. Introduction Most biological sample analyses require either the removal of cells from a biological fluid, such as the removal of blood cells from whole blood to leave purified plasma, or cell concentra- tion for downstream analyses. For instance, when performing blood analysis in medical laboratories, the blood cells are separated from the whole blood collected from a patient by centrifugation and the blood plasma is analyzed for electrolyte concentration, glucose, lactate, total cholesterol, etc. These sequential procedures on single batch blood collections can take up to several hours. Recently, the iSTAT system has been introduced as a point of care diagnostic device 1 for blood analysis for both bedside and outpatient monitoring and has removed some of the laboratory bottlenecks. However, there is a need for a system, which can separate blood plasma from whole blood and measure the concentration of the clinically relevant proteins in continuous, real time fashion. For example, according to several studies, 2–10 cardiac surgery can produce systemic inflammatory responses in a variety of ways, especially when cardiopulmonary bypass (CPB) is used. CPB induces complex inflammatory responses characterized by complement, neutrophil, and platelet activation, and the release of pro-inflammatory cytokines. In general, exposure of blood to nonphysiological surfaces of the heart–lung machine, hypothermia, surgical trauma, and ischemia–reperfusion of the involved tissues are considered as main factors causing postoperative complications. These complications include vital organ dysfunction that can lead to multi-organ failure and even death. 8,10,11 The intensity of the inflammatory response appears to be directly correlated with the severity of CPB-related morbidity. 2,8,10–13 Currently, there is no effective method for preventing this systemic inflammatory response syndrome in cardiac surgery patients undergoing CPB. Therefore, there is an unmet medical need to develop safe and effective therapeutic diagnostics to monitor this inflammatory response in real time, while the surgery is proceeding to better understand how CPB and surgical or anesthetic procedures might be modified to prevent its occurrence. Current technology provides measure- ments of the effects of cardiopulmonary bypass on activation of complements, neutrophils, platelets, and cytokines hours or days post-surgery. More immediate measurements would aid in understanding the mechanisms of cellular activation, and modify surgical and perfusion protocols for minimizing adverse effects of cardiopulmonary bypass. To accomplish immediate measurements of the clinically relevant proteins, such as cytokines and complements, two functions have to be obtained in a continuous, real time fashion: blood plasma separation and detection of proteins. The objective of this study is to develop a microfluidic device for continuous, real time blood plasma separation 14 for the application of the online monitor- ing of inflammatory responses (cytokines, complements) during the CPB procedure. Research activities involving on-chip a 205, Hallowell, Department of Bioengineering, The Pennsylvania State University, University Park, PA, USA. E-mail: sxy154@psu.edu; Fax: +1 814-863-0490; Tel: +1 814-865-6748 b C7529, Departments of Pediatrics, Surgery, and Bioengineering, The Pennsylvania State University, Penn State Milton S. Hershey Medical Center, Penn State College of Medicine, Penn State Children’s Hospital, Hershey, PA, USA. E-mail: aundar@psu.edu; Fax: +1 717-531-0355; Tel: +1 717-531-6706 c 224, Hallowell, Department of Bioengineering, The Pennsylvania State University, University Park, PA, USA. E-mail: jdzbio@engr.psu.edu; Fax: +1 814-863-0490; Tel: +1 814-865-8090 PAPER www.rsc.org/loc | Lab on a Chip This journal is ß The Royal Society of Chemistry 2006 Lab Chip, 2006, 6, 871–880 | 871