High Aspect Ratio Sub-Micrometer Channels Using Wet Etching: Application to the Dynamics of Red Blood Cell Transiting through Biomimetic Splenic Slits

TL;DR

This study introduces a simple, cost-effective microfluidic device with high aspect ratio sub-micrometer slits to observe red blood cell deformation, revealing new insights into cell mechanics and differences in healthy versus diseased cells.

Contribution

It presents a novel, inexpensive fabrication method for high aspect ratio microchannels and demonstrates their use in studying RBC dynamics under physiological conditions.

Findings

RBCs exhibit distinct deformation modes in splenic-like slits.

Sickle cell RBCs show increased cytoplasmic viscosity.

Massive trapping of spherocytic RBCs observed.

Abstract

Nanoparticles delivering drugs, disseminating cancer cells, and red blood cells (RBCs) during splenic filtration must deform and pass through the sub-micrometer and high aspect ratio interstices between the endothelial cells lining blood vessels. The dynamics of passage of particles/cells through these slit-like interstices remain poorly understood because the in vitro reproduction of slits with physiological dimensions in devices compatible with optical microscopy observations requires expensive technologies. Here, novel microfluidic PDMS devices containing high aspect ratio slits with sub-micrometer width are molded on silicon masters using a simple, inexpensive, and highly flexible method combining standard UV lithography and anisotropic wet etching. These devices enabled revealing novel modes of deformations of healthy and diseased RBCs squeezing through splenic-like slits (0.6--2 um 5--10 um 1.6--11 $\mu$m3) under physiological interstitial pressures. At the slit exit, the cytoskeleton of spherocytic RBCs seemed to be detached from the lipid membrane whereas RBCs from healthy donors and patients with sickle cell disease exhibited peculiar tips at their front. These tips disappeared much slower in patients' cells, allowing estimating a threefold increase in RBC cytoplasmic viscosity in sickle cell disease. Measurements of time and rate of RBC sequestration in the slits allowed quantifying the massive trapping of spherocytic RBCs.