BIO5: Development an in Vitro System To Investigate The Impact Of Pulsatility On Endothelial Von Willebrand

Background: Non-surgical bleeding is one of the most common adverse events associated with continuous flow (CF) ventricular assist devices (VADs), which is linked to shear mediated degradation of von Willebrand factor (vWF). vWF degradation has traditionally been studied in the context of supraphysiological shear stresses within the VAD. However, recent evidence suggests that loss of pulsatility is a significant contributing factor for vWF degradation and in vitro systems are needed to study this mechanism. Methods: A compact, pneumatically driven, in vitro human arterial endothelial cell culture model, that incorporates directional control, resistance, compliance, and pressure and flow measurements was developed (Fig. 1). The device has a microfluidic channel for seeding human arterial endothelial cells (HAECs). It was cast in PDMS from a mold and plasma bonded to a glass cover slip to permit imaging. Flow and pressure data were collected using custom LabView scripts. Results: Our model was able to simulate physiological pulse pressure, flow profile, and shear rates for normal pulsatile flow (Fig 2A). By altering the compliance element volumes, we also simulated the flow, pressure, and shear profiles experienced with CF-VAD support (Fig 2B). HAECs were successfully cultured in the microfluidic channel and imaged under microscopy (Fig 3). Conclusion: By being able to modulate flow, shear, and pressure magnitude and amplitude, our model system will enable the study of how pressure and flow characteristics affect vWF secretion, unraveling, and degradation. These data may inform changes to VAD flow modulation or VAD design to minimize bleeding. Figure 1: In vitro perfusion loop model Figure 2: Pressure, flow, and shear profiles produced to simulate (A) normal/pulsatile and (B) CF-VAD supported/continuous flow conditions Figure 3: (A) Phase contrast and (B) DAPI microscopy images of Human aortic endothelial cells (HAECs) cultured in the microfluidic channel