BIO29: A Microfluidic Model Of Extracorporeal Circuit Thrombosis

Abstract

Purpose: Cardiovascular medical devices such as extracorporeal membrane oxygenation (ECMO) machines are critical for the treatment and management of cardiorespiratory illnesses. However, blood contact with medical device biomaterials causes dangerous blood clot formation (thrombosis). In ECMO, blood clots can grow large enough to occlude circuitry and fail the device, or clots may dislodge and potentiate stroke and embolism in patients. While medical device thrombosis is clinically managed with systemic anticoagulation, thrombosis and its associated complications still exist, and anticoagulation frequently worsens patient outcomes by causing severe bleeding. There remains an urgent need to understand the mechanisms of biomaterial thrombosis and develop thromboresistant biomaterials. We hereby demonstrate a novel biomaterial thrombosis on-a-chip model system for real-time, high-throughput evaluation of ECMO thrombosis. Methods: Our study combines computational fluid dynamics (CFD) and microfluidic technology to design in vitro models with customizable, clinically relevant biomaterials and flow conditions, which are two key factors influencing thrombus formation. ANSYS Fluent was used to model the flow parameters within ECMO tubing and tubing-connector junctions (TCJ). Microfluidic devices were fabricated using standard photolithography and soft lithography with unplasticized polyvinylchloride (UPVC) and polycarbonate (PC), replicating ECMO tubing and TCJ respectively. Biomaterial thrombosis was visualized in real-time via confocal microscopy, and analyzed as the total fluorescent area of platelet adhesion (CD41-FITC) and human fibrin/ogen (AF647) accumulation. Results: CFD revealed that shear rates of 500 – 5000 s-1 and decelerating flow regimes are relevant to ECMO tubing thrombosis. Microfluidic evaluation at such conditions showed that compared to the low platelet adhesion observed at continuous high shear (3000 s-1) (340 ± 266 µm2), platelet adhesion increased by 16-fold at continuous low shear (1000 s-1) (5510 ± 3631 µm2), increased 5-fold at deceleration into high shear (1703 ± 598 µm2), and increased 2.7-fold at stagnant into high shear conditions (912 ± 308 µm2). These results may be used to guide clinical practice and ECMO redesign to minimize low, decelerating shear. Conclusion: We have developed a model system capable of evaluating biomaterial thrombosis at tailorable, clinically relevant biomaterial and flow combinations. Additionally, this system may be used to test novel anti-thrombotic biomaterials or patient-specific blood-biomaterial compatibility. Ultimately, this model will improve ECMO treatment efficacy by advancing the field’s knowledge in scientific mechanisms underlying biomaterial thrombosis, inform clinicians of thrombotic flow regimes which should be minimized, and identify thrombotic biomaterial and flow combinations to guide bioengineers to design the next generation of safer ECMO.Figure 1. A microfluidic device incorporating extracorporeal circuit biomaterials is used to visualize thrombus formation under clinically relevant flow.