Particulate Blood Analogues Reproducing the Erythrocytes Cell-Free Layer in a Microfluidic Device Containing a Hyperbolic Contraction

Abstract

The interest in the development of blood analogues has been increasing recently as a consequence of the increment in the number of experimental hemodynamic studies and the difficulties associated with the manipulation of real blood in vitro because of ethical, economical or hazardous issues. Although one-phase Newtonian and non-Newtonian blood analogues can be found in the literature, there are very few studies related to the use of particulate solutions in which the particles mimic the behaviour of the red blood cells (RBCs) or erythrocytes. One of the most relevant effects related with the behaviour of the erythrocytes is a cell free layer (CFL) formation, which consists in the migration of the RBCs towards the center of the vessel forming a cell depleted plasma region near the vessel walls, which is known to happen in in vitro microcirculatory environments. Recent studies have shown that the CFL enhancement is possible with an insertion of contraction and expansion region in a straight microchannel. These effects are useful for cell manipulation or sorting in lab-on-chip studies. In this experimental study we present particulate Newtonian and non-Newtonian solutions which resulted in a rheological blood analogue able to form a CFL, downstream of a microfluidic hyperbolic contraction, in a similar way of the one formed by healthy RBCs.

Keywords: blood analogue; cell-free layer; hemodynamics; microfluidics; rheology.

Figure 1

A schematic top-view of the microchannel. The width ($w_u$) and contraction length (l) are 400 µm. The width of the exit of the contraction region ($w_c$) and the depth of the channel (h) were 15 µm.

Figure 2

A view of experimental set-up: an inverted microscope (IX71, Olympus) and a 10× objective lens, combined with a high-speed camera (i-SPEED LT, Olympus). The PDMS microchannel was placed on the stage of the microscope where the flow rate (Q) of the working fluids was kept constant (at 5 and 20 µL/min) by means of a syringe pump (Harvard Apparatus PHD ULTRA).

Figure 3

(a) An original image of polymethylmethacrylate (PMMA) particle flow and (b) its minimum intensity image; the vertical line is the measuring position placed at 300 µm from the contraction exit.

Figure 4

Steady shear viscosity curves for the viscoelastic solution with and without PMMA particles and for the Dx40 solution. The minimum torque line represents the limit of accuracy of the rheometer.

Figure 5

Images of (a) Red Blood Cells (RBCs) flow, B1, (b) two-phase viscoelastic solution flow, X2 and (c) PMMA particles in Dx40 flow, D2. Left: an original image; Right: a minimum intensity image.

Figure 6

Illustration of the RBCs deformability through hyperbolic microchannel where F${}_{\text{extensional}}$ represents the strong extensional force applied to the RBCs. The same forces was applied to the PMMA particles however without present any deformation.

Figure 7

Comparison of mean CFL thickness in downstream region between the fluid B1, RBCs suspended in Dx40; X2, particulate-viscoelastic fluid and D2, PMMA particles in Dx40, as a function of flow rate, 5 µL/min and 20 µL/min. The error bar means 95% confidence interval.