Haematocrit heterogeneity in blood flows past microfluidic models of oxygenating fibre bundles

Abstract

Blood oxygenators act as an extracorporeal artificial lung during certain types of cardiac surgery and intensive care therapies. Inside these devices, blood is forced to flow across an oxygenating bundle, encountering interstitial gaps comparable to those typical of the microvasculature. Despite the wellknown effects of such length scales on haemorheology and red blood cell (RBC) behaviour, these are generally overlooked in oxygenator modelling and design; it is persistently assumed that RBCs are homogeneously distributed throughout the oxygenating bundle, independently of their microstructure arrangement or main flow directions. The goal of this study is to provide preliminary experimental evidence of heterogeneous RBC distributions inside oxygenating fibre bundles. To this end, a number of microchannels were manufactured inspired by actual oxygenating devices, considering simplified versions of their microstructure. These comprise staggered arrays of micro pillars, which were perfused with RBC suspensions, with feed haematocrit (Ht) and velocities relevant for clinical use. The microchannels were imaged using a microscope and high-speed camera to accurately capture cell distribution. The imaged blood flows revealed the non-uniform nature of RBC distributions in the arrays, characterised by local Ht gradients particularly around the O2 sources inside the bundle. These heterogeneous distributions should be accounted for during oxygenator design, as RBC concentration plays a key role in O2 transport and, ultimately, overall device performance

Flows of healthy and hardened RBC suspensions through a micropillar array

“…Several microfluidic platforms have been utilized to examine the role of deformability in RBC flows but their geometries tend to be simplified. In the present study, we extend our previous work on healthy RBC flows in micropillar arrays [1] to probe the effect of impaired RBC deformability on the velocity and haematocrit distributions in microscale RBC flows. Healthy and artificially hardened RBC suspensions at 25% haematocrit were perfused through the micropillar array at various flow rates and imaged.…”

“…Motivated by our previous work on RBC flows in bifurcating geometries and on the role of RBC deformability on microchannel flows [22], we extend the work of Gomez Bardon et al [1] to elucidate the effect of deformability on the transport of dense suspensions of RBCs in the interstitial space of a microfluidic pillar array. The flow therein exhibits interesting kinematics featuring curvature, converging and diverging flow regions as well as stagnation points.…”

“…Stauber et al [40] employed a microchannel with a dense array of posts to mimic alveolar capillary networks and studied the motion of RBCs therein. Gomez Bardon et al [1] used microfluidic devices with pillar arrays to study the blood flow past oxygenator fibers with a view to improve modelling and design of extracorporeal artificial lungs for intensive care therapies. They examined the heterogeneous distribution of RBCs in different pillar array arrangements and their implications for oxygen delivery and device performance.…”

Advances in Microfluidics for Single Red Blood Cell Analysis

“…Experiments related to the heterogeneity in RBC distribution indicate a non-uniform nature in microfluidic platforms. These are characterized by local hematocrit gradients and are assumed to impact the cellular oxygen distribution [180], as well as the relationships between RBC deformability and hematocrit partitioning in bifurcating channels [181].…”

Advances in extracorporeal membrane oxygenator design for artificial placenta technology

“…However, reducing the number of connectors and corners does not ultimately solve a fundamental weakness of hollow‐fiber membrane oxygenators, which is the inability to precisely control the blood flow path within the oxygenator. Computational fluid modeling of blood flow around individual hollow fibers has shown significant flow heterogeneity, even in uniformly distributed hollow‐fiber membranes 76,77 …”