Dr Wilbur Lam, Emory University School of Medicine, USA
Originally thought to be a simple genetic disease that causes misshaping and increased rigidity of red cells (RBCs), sickle cell disease (SCD) is now known to involve numerous biophysical and biochemical interactions among blood cells, endothelial cells, and soluble factors (e.g. cytokines, coagulation factors, etc). Indeed, decades of research have qualitatively shown that alterations in the biophysical properties, such as cell deformability and cell adhesion, lead to interactions among sickle RBCs, platelets, reticulocytes, white cells (WBCs), and endothelial cells and each of these likely contributes to microvascular occlusion, hemolysis, and endothelial dysfunction under different conditions. Although in vivo animal models have vastly improved our understanding of these interactions in SCD, complementary in vitro systems have the potential to offer valuable quantitative insights in how biophysical properties influence SCD pathophysiology. However, due in part to lack of adequate technology, conventional in vitro techniques focus on a singular, isolated aspect of SCD pathophysiology (e.g., RBC adhesion, deformability, endothelial cell physiology). Therefore, an in vitro system that accurately takes into account the cellular, physical, and hemodynamic environment of the microcirculation is needed as a research enabling platform for SCD. To that end, our interdisciplinary hematology bioengineering laboratory has recently developed an in vitro “endothelialized” microfluidic microvasculature model that recapitulates and integrates the ensemble of pathophysiological cellular interactions that occur in SCD (Tsai et al, JCI, 2012; Myers et al, JoVE, 2012). Leveraging microsystems technology from the computer chip industry, we used similar techniques to create this “microvasculature-on-a-chip.” Specifically, we used a single-mask microfabrication process combined with standard endothelial cell culture techniques to develop a microvascular sized (<30 µm) system that incorporates a confluently cultured endothelial cell monolayer that spans the entire 3D inner surface area of the microdevice. The microvasculature-on-a-chip fully integrates blood cell-endothelial cell adhesion, cellular aggregation, cellular mechanical properties (i.e., size, deformability, etc.), microvascular geometry, oxygen tension, and hemodynamic flow conditions, and is therefore suitable for quantitative analyses of pathophysiological processes that occur in SCD. In this talk, I will discuss how microfluidic devices are developed and how they are useful in SCD research, the capabilities and limitations of microfluidic systems including the microvasculature-on-a-chip, and the specific questions in SCD that these microdevices can address