A Flow-Integrated Microtissue Array System for Tissue Mechanics Study
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Biofabrication enables fantastic applications, such as 3D cell culture, disease modeling and drug screening. The current thesis describes the development ofa new microfabricated device, focusing on the role of the physical forces of platelets in clot formation and drug screening for haemostasis disorders. The challenge of correctly diagnosing a coagulation disorder during surgery and anesthetics operation remains to the treatment of bleeding complication. The forces generated by platelets are thought to regulate haemostasis, but previous in vitro systems for platelet studies were not able to recapitulate the mechanical forces which occur in vivo. Thromboelastography (TEG) and rotation thromboelastography (ROTEM) are popular mechanical testing methods used in the clinics, due to their ability to monitor the entire coagulation stages, small sample requirements, and rapid readout. However, they ignore physiological flow and the subendothelial collagen matrix. As a result, these systems are not able to diagnose certain coagulation disorders, such as von Willebrand’s syndrome and the disorder of primary hemostasis. Here we report a new microchip combining the advantages of force sensing microposts and microfluidic channels to measure the contraction force of an aggregation of platelets adhering to a collagen matrix. The design is based on microtissue force gauge devices with submillimeter 3D cell-populated microtissues in arrays of poly(dimethylsiloxane) (PDMS) microwells. In each microwell, cells spontaneously contract and assemble collagen. Microcantilevers serve both as mechanical support and as force sensors that can report in-situ contraction force generated by the cell population. Resident cells in the microtissue are removed through trypsinization, resulting in the exposure of an array of collagen matrix proteins, each mimicking the subendothelial matrix at a vascular injury site. Platelets are activated by the shear stress of flowing plasma and captured by micro collagen substrate arrays to form individual microclots. The generation of contraction force during clot formation and retraction were observed during the growth of platelet micro-clots. Finally, the effects of abciximab and ADP on platelet adhesion and contraction were demonstrated with this microchip.