Microfluidic and Spleen-on-a-Chip Studies of Sickle Cell Disease

Healthy human red blood cells (RBCs) gradually degrade over their lifespan of ~120 days. However, sickle cells - RBCs from sickle cell disease (SCD) patients - degrade much faster within their much-shortened lifespan of ~10-20 days. Understanding the underlying mechanisms of RBC senescence in health and disease is crucial for studying many RBC diseases. Both normal RBCs and sickle cells experience repeated cycles of hypoxia and mechanical fatigue. To investigate the impact of these challenges on RBC damage and degradation accumulation, we developed in vitro microfluidic assays for testing RBCs under cyclic hypoxia loading and/or cyclic mechanical loading. Moreover, spleen plays a crucial role in maintaining the balance between RBC formation (erythropoiesis) and removal. Altered RBCs are cleared from circulation through splenic RBC retention and elimination, which mainly occur in open circulation, where RBCs flow through macrophages and inter-endothelial slits (IESs). Specifically, we developed an in-vitro oxygen-mediated spleen-on-a-chip platform, combined with in-silico simulations and in-vivo/ex-vivo observations to study spleen function and antisickling drug efficacy. Our results provide mechanistic insights into how spleen maintains its homeostatic balance between splenic RBC retention and elimination, and how disruptions in this balance could lead to anemia, splenomegaly, and acute splenic sequestration crisis in SCD.

Learning Objectives:

1. Summarize the root cause of sickle cell disease and the importance of studying sickle cell (i.e., red blood cell from sickle cell disease patient) behavior under hypoxia.  

2. Explain why the microfluidic assays developed for testing accumulated red blood cell degradation due to the challenges of cyclic hypoxia and mechanical fatigue: device setup and key results.

3. Summarize the oxygen-mediated spleen-on-a-chip platform for studying the retention of sickle cells by splenic interendothelial slits and the adhesion and elimination of sickle cells by macrophages: device setup and key results.