A Microfluidic Device For Blood Cell Analysis Using Acoustic Microstreaming

Summary: A fully integrated microfluidic device was developed to automatically separate human blood cells and perform cell morphology studies on a chip. The device was designed based on acoustic microstreaming and hydrodynamic separation principles to separate Red Blood Cells (RBCs) from White Blood Cells (WBCs). Acoustic microstreaming achieved highly efficient blood cell separation (89% rate) similar to that of conventional centrifugation. The device successfully fractionated blood components and the obtained images of various abnormal blood cells including sickle cells, immature granulocytes are indication of a patient's health status. The device presents a more practical way of blood cell analysis compared to conventional blood smears. Background: Complete blood analysis typically includes identification and differentiation of various blood cells. The blood morphology test is amongst the most commonly performed blood tests in diagnostics. Currently blood smears have been used for patient blood screen. However, the preparation of blood smear slides is time-consuming and labor-intensive. Microfluidic devices for blood fractionation have been developed recently, but very few have been used for morphology analysis. Methods: The device (20x2x0.05 mm) is designed based on three principles: particle retention, hydrodynamic separation, and acoustic microstreaming. The central channel consists of a set of microfilters with various pore sizes (30 µm, 20 µm, 10 µm) to retain WBCs in the WBC chamber. Hydrodynamic filters are also used to separate RBCs from WBCs due to small inertial force of RBCs. The side channel consists of cavities to store air bubbles to generate acoustic microstreaming. The device was made of PDMS using soft lithography. Results: Both particle retention and hydrodynamic filters successfully separated WBCs and RBCs. However, these filters could be clogged easily by cells. Cell separation based on acoustic microstreaming achieved highly efficient blood cell separation (89% rate) and showed superior advantages: 1) no cell clogging issues; 2) no moving parts; 3) simple in design; 4) easy to integrate and fabricate; 5) low cost. Using this microvortex technique, WBCs can be separated and concentrated in the area close to the cavity, making it easy to perform cell morphology analysis. Various types of WBCs, such as lymphocytes, neutrophils, and monocytes, were identified. Normal RBCs as well as some abnormal RBCs (such as sickle cells) were seen in the RBC chamber.  Conclusion: The microchannel device has successfully separated blood cells based on their difference in size, inertial force, mass, and hydrodynamic properties, followed by blood morphology. Three microfluidic cell separation techniques (particle retention, hydrodynamic, and acoustic microstreaming) were investigated. It was found that acoustic microstreaming achieved highly efficient blood cell separation similar to that of conventional centrifugation technique.