(247f) High-Throughput Measurement of the Human RED Blood CELL Shear Modulus Distribution

Deformability is a critical feature of red blood cells (RBCs) within their 100-120 day life-span through the blood circulation system, and it is a particularly important factor in their flow through the microcirculation capillaries or the splenic sinusoids. Deformability is affected by many pathological conditions and its alteration can impact the pathophysiology of many diseases. While primary reasons for altered deformability are hereditary, mutation, or parasite invasion, there are also many secondary biochemical pathways which influence RBC morphology, biochemistry, and biomechanics. As a result, RBC deformability is altered in many blood related diseases such as diabetes, sepsis, metabolic syndrome. For example, it was recently discovered that, even neurodegenerative diseases could be correlated to the deformability of RBCs due to the interrelation of neural activity and blood circulation.

RBC structure and deformability are largely governed by the membrane shear modulus. State-of-the-art methods to measure the shear modulus of RBCs are not high-throughput and, microfluidic platforms for high-throughput measurements of RBC mechanical properties have not yet enabled measurement of the shear modulus. These limitations challenge the development of diagnostic devices based on RBC shear modulus biomarkers. In this talk, we will demonstrate a high-throughput microfluidic platform, coupled with high-fidelity simulations to address this significant gap in technology. In contrast with existing technologies, this approach allows us to measure the shear modulus of individual RBCs and generate shear modulus distributions (for a given individual or multiple individuals) including measurements of thousands of cells in a few seconds of experimental data acquisition.

For the computational fluid dynamics, we develop immersed boundary simulations in periodic channel domains matching the microfluidics to find the steady-state shape. We use the well-known Skalak model for modelling the RBC membrane and we assume, as is usual, that these systems are largely surface incompressible. We then utilized the steady-state shapes to generate a surface for data interpretation relating the three important non-dimensional parameters: the Taylor deformation (Ta) , the confinement (, and the capillary number (based on cell velocity) Ca_cell. We then performed high-throughput experimental visualizations of RBCs under flow from a variety of blood donors. The experimental setup consisted of a custom poly-dimethylsiloxane (PDMS) and glass microfluidic chip, as well as flow control and image acquisition instruments. RBCs were imaged as they traveled through a 7×7×1000 μm³ constriction at velocities of 2-10 mm s^-1. The experimentally measured, steady-state Taylor deformation of each RBC was compared to the aforementioned, computationally generated Taylor deformation versus confinement projection, and used to extract the nondimensional RBC capillary number and hence shear modulus. We demonstrate that our platform provides mean values of the modulus that are in quantitative agreement with other low throughput measurement techniques in the literature (e.g optical tweezers), but that the distribution for each donor follows a broad lognormal distribution. Moreover, a fresh blood distribution can show a mean shear modulus near 6.6 N/m, but after 5 weeks of storage, the mean shear modulus increases to 34 microN/m. To the best of our knowledge, this work is the first to measure the shear moduli of thousands of RBCs and we will finish the talk with applications of the device in measuring biomarkers for disease.