Incoherent light transport in an anisotropic random medium: a probe of human erythrocyte aggregation and deformation.

This paper investigates the flow induced disaggregation, deformation and orientation of several modified human red blood cells suspended in concentrated, physiological like conditions (volume fraction in erythrocytes of 0.4). The aim is to determine simultaneously, and under flow, the aggregate sizes as well as the deformation and orientation of the cells. The measurement method uses steady, incoherent, unpolarized light transport while the sample is sheared in a flow cell controlled by a rheometer. Several blood samples were prepared to alter the erythrocyte's aggregating, deformability and shape properties. The measurements using these samples show a clear relationship between the intrinsic properties of the cells and the evolution of aggregate sizes, average cell orientation and anisotropy as a function of the applied shear, which may lead to clinical applications. In other words, the careful analysis of the incoherent light transport in concentrated media provides quantitative insight into their microscopic details. In particular, the topological properties (average anisotropy and orientation) and size of the suspended objects can be determined.

Steady light transport under flow: characterization of evolving dense random media.

We describe in this letter a new rheo-optical apparatus able to measure the photon transport length l* in an evolving random medium. First, the appropriate solution of the diffusion equation for oil in water, stable, micron-sized emulsions is compared successfully with the measured spatial distribution of incoherent backscattered light given by the new apparatus. Further validation is provided using stable samples of varying sizes and volume fractions (1% to 64%) and comparing measurements with Mie-Percus-Yevick calculations based on independent small-angle light scattering (SALS) measurements. As a typical example application of the system, the emulsification of a different oil in water system is studied in situ and dynamically. The continuous temporal measurements show the decrease of the average size versus time, in excellent quantitative agreement with independent SALS measurements. This evidences that this system is able to probe continuously and nonintrusively the microscopic and macroscopic flow-induced organization of suspensions.