Extensional flow of blood analog solutions in microfluidic devices

Abstract

In this study, we show the importance of extensional rheology, in addition to the shear rheology, in the choice of blood analog solutions intended to be used in vitro for mimicking the microcirculatory system. For this purpose, we compare the flow of a Newtonian fluid and two well-established viscoelastic blood analog polymer solutions through microfluidic channels containing both hyperbolic and abrupt contractions/expansions. The hyperbolic shape was selected in order to impose a nearly constant strain rate at the centerline of the microchannels and achieve a quasihomogeneous and strong extensional flow often found in features of the human microcirculatory system such as stenoses. The two blood analog fluids used are aqueous solutions of a polyacrylamide ͑125 ppm w/w͒ and of a xanthan gum ͑500 ppm w/w͒, which were characterized rheologically in steady-shear flow using a rotational rheometer and in extension using a capillary breakup extensional rheometer ͑CaBER͒. Both blood analogs exhibit a shear-thinning behavior similar to that of whole human blood, but their relaxation times, obtained from CaBER experiments, are substantially different ͑by one order of magnitude͒. Visualizations of the flow patterns using streak photography, measurements of the velocity field using microparticle image velocimetry, and pressure-drop measurements were carried out experimentally for a wide range of flow rates. The experimental results were also compared with the numerical simulations of the flow of a Newtonian fluid and a generalized Newtonian fluid with shear-thinning behavior. Our results show that the flow patterns of the two blood analog solutions are considerably different, despite their similar shear rheology. Furthermore, we demonstrate that the elastic properties of the fluid have a major impact on the flow characteristics, with the polyacrylamide solution exhibiting a much stronger elastic character. As such, these properties must be taken into account in the choice or development of analog fluids that are adequate to replicate blood behavior at the microscale.

In vitro blood flow and cell-free layer in hyperbolic microchannels: Visualizations and measurements

“…The flow behaviour under extensional flow is known to be different from that under shear flow conditions. Sousa et al (2011) 12 investigated the flow behaviour of two viscoelastic fluids, known as blood analogue fluids, and concluded that despite their similar shear rheology, the behaviour under a strong extensional flow is different due to differences in the elastic components of both solutions. Recently, Brust et al (2013) 15 also found that blood plasma revealed a different rheological behaviour when experiencing a shear or an extensional flow.…”

“…Recently, Lee et 12 studied the effect of the extensional flow in a hyperbolic converging microchannel using animal blood, human blood and blood analogue fluids, respectively. The importance to study these types of geometries is mainly due to their ability to impose a constant strain rate along the centreline 13,14 and consequently generate strong extensional flows.…”

Human red blood cell behavior under homogeneous extensional flow in a hyperbolic-shaped microchannel

“…The rationale behind the use of hyperbolic contractions is their ability to impose a nominally constant strain rate ð_ e ¼ du x =dx ¼ constant 6 ¼ 0Þ along the centerline as discussed by James 23 for an axisymmetric configuration. Relevant works in the context of blood flow are those of Sousa et al 24 and Lee et al 25 who studied the effect of the extensional flow in hyperbolic converging microchannels using artificial polymer-based blood analog fluids and in vitro rabbit blood, respectively. Sousa et al 24 used hyperbolic contractions of different Hencky strains to show that two well-established blood analogue fluids with identical steady-shear viscosity, but different extensional rheology, behave very differently when submitted to conditions equivalent to the microcirculation.…”

Cell seeding chamber for bone graft substitutes

“…Sometimes solutions of polyacrylamide are used [3][4] [5]. For testing the basic functionality of the cell seeding chamber a solution of Water an Xanthan (0,05 ma%) has been chosen [5]. The viscosity of the blood substitute was checked with a rheometer Mars 2 (Haake).…”

“…Non-newtonian blood substitutes are often based on polymer solutions, for example mixtures of water and glycerin or mixtures of water, glycerin and xathan. Sometimes solutions of polyacrylamide are used [3][4] [5]. For testing the basic functionality of the cell seeding chamber a solution of Water an Xanthan (0,05 ma%) has been chosen [5].…”