Sickle cell vasoocclusion and rescue in a microfluidic device

Abstract

The pathophysiology of sickle cell disease is complicated by the multiscale processes that link the molecular genotype to the organismal phenotype: hemoglobin polymerization occurring in milliseconds, microscopic cellular sickling in a few seconds or less [Eaton WA, Hofrichter J (1990) Adv Protein Chem 40:63-279], and macroscopic vessel occlusion over a time scale of minutes, the last of which is necessary for a crisis [Bunn HF (1997) N Engl J Med 337:762-769]. Using a minimal but robust artificial microfluidic environment, we show that it is possible to evoke, control, and inhibit the collective vasoocclusive or jamming event in sickle cell disease. We use a combination of geometric, physical, chemical, and biological means to quantify the phase space for the onset of a jamming event, as well as its dissolution, and find that oxygendependent sickle hemoglobin polymerization and melting alone are sufficient to recreate jamming and rescue. We further show that a key source of the heterogeneity in occlusion arises from the slow collective jamming of a confined, flowing suspension of soft cells that change their morphology and rheology relatively quickly. Finally, we quantify and investigate the effects of small-molecule inhibitors of polymerization and therapeutic red blood cell exchange on this dynamical process. Our experimental study integrates the dynamics of collective processes associated with occlusion at the molecular, polymer, cellular, and tissue level; lays the foundation for a quantitative understanding of the rate-limiting processes; and provides a potential tool for optimizing and individualizing treatment, and identifying new therapies.

Flow-induced clustering and alignment of vesicles and red blood cells in microcapillaries

“…Thus, the shape deformation of RBCs in microvessels plays a key role in the regulation of oxygen delivery. The deformability of RBCs can be reduced, for example, in diseases such as diabetes mellitus (8) and sickle cell anemia (9).…”

“…In contrast, we focus here on flows in narrow capillaries, where the tube diameter just exceeds the cell size. Our study is motivated by recent developments of microfluidic devices (31) that allows the investigation and manipulation of individual liquid droplets (32) and cells (8,9,33,34). We used computer simulations to study RBC-like vesicles, which have the same reduced volume as real RBCs, but a lower bending rigidity and shear modulus.…”

Cellular normoxic biophysical markers of hydroxyurea treatment in sickle cell disease

“…It is, therefore, possible that the effect of HbF induction is more prominent at hypoxia, because its principal biochemical effect is to inhibit hypoxia-induced HbS polymerization. Multiple studies indeed show that, in hypoxic conditions, the effect of the HbF level correlates with the kinetic biophysical properties (29,30,50). These same studies do not show any drug effect for properties such as blood rheology measured at normoxic condition.…”

“…As the primary consequence of mutation in the β-globin chain gene is formation of HbS fibers within the cytosol under low-oxygen environment, biophysical studies have been mainly focused on identifying biomarkers under hypoxic condition. Measuring rheological properties of the blood under hypoxia has been suggested as one such indicator of the propensity for vasoocclusive crisis in sickle patients (29,30). Here, we hypothesize that biophysical properties of individual RBCs of sickle patients at normoxia, including morphology and biomechanical properties, could better characterize physiological changes due to HU treatment than molecular-level markers.…”

Monitoring Biological Cell Flow within a Mimicking Capillary Device with Impedance Measurement

“…When the sixth Glutamic acid (Glu) of HBS is replaced by Valine (Val), RBCs change their shape from oval biconcave disk to sickle, losing their deformability, leading to vaso-occlusive crisis [2]. We propose to diagnose the presence of sickle RBCs, by the analysis of RBC transit time in microfluidic channels, which dimensions mimicking the blood capillaries.…”