A Microfluidic Device for Measuring Clot Size and Force Generation

Undergraduate #324
Discipline: Technology and Engineering
Subcategory: Biomedical Engineering

Adriane M. Fura - University of Washington
Co-Author(s): Nikita Taparia and Nathan Sniadecki, University of Washington, Seattle

Vascular injury causes platelets to form hemostatic plugs. Shear and exposure of collagen activate platelets, which adhere and contract to protect a clot from mechanical forces. The role of collagen, and the anticoagulants heparin and ASA which inhibit thrombin and thromboxane A2 (TxA2) respectively, are not fully understood1. Our lab has designed a microfluidic device to measure clot forces. In my REU I built these devices and analyzed clot forces and area. This clot-on-a-chip technology can shed light on the clotting process and diagnose patient clotting issues. We use soft lithography to build microfluidic channels with block-post sensors2. Blocks generate shear gradients, inducing platelet adhesion. Clots grow towards the post and contract, pulling the post closer. The post is a flexible beam of known stiffness and follows Hooke’s law. Fluorescence microscopy allows post deflection to be analyzed with MATLAB code, and phase images monitor area. First, channels were coated with and without collagen. Then, channels were collagen -coated and blood inhibited with heparin or ASA. Blood was incubated with 15 USP heparin lithium in H2O or 0.3 mM ASA in DMSO for 20 min. Clots in uncoated channels had lower force than in collagen-coated channels. Blood with ASA in DMSO had less platelet adhesion and contraction than in blood incubated with DMSO. Blood with heparin in H2O had lower force but higher clot area compared to only H2O. Reduced force of clots formed in uncoated channels relative to collagen-coated channels suggests that collagen is important in force. Inability of platelets to adhere or produce normal force with ASA indicates that TxA2 promotes platelet aggregation and force. Heparin reduced force but not platelet aggregation, thus thrombin is involved in force generation only. Our microfluidic device provides real-time monitoring of platelet aggregation and forces. This technology is a promising diagnostic tool for treatment of patients with clotting issues. Future work will look at the role of each receptor in force generation.

References: 1) Grey, E., Hogwood, J., Mulloy, B. 2012. The anticoagulant and antithrombotic mechanisms of heparin. Handb Exp Pharmacol. (207):43-61.
2) Ting, L., Feghhi, S., Karchin, A., Tooley, W., White, N., Sniadecki, N. 2013. Clot-on-a-chip: A microfluidic device to study platelet aggregation and contractility under shear. Blood 122 (21):2363.

Funder Acknowledgement(s): NSF: Biomechanics and Mechanobiology (BMMB) program in the Civil, Mechanical and Manufacturing Initiative (CMMI) Division.

Faculty Advisor: Nathan Sniadecki, nsniadec@uw.edu