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Dr Timm Krüger, Exploiting particle deformability for sorting and focusing in microfluidic devices

Date: Fri 30 May 2014, 14:30 - 15:30

Location: Nanoforce Seminar Room (Joseph Priestley Building)

Dr Timm Krüger
University of Edinburgh

Abstract
Suspensions of deformable particles, e.g. capsules or red blood cells (RBCs), show a rich dynamical behaviour in external flows. The particle deformability leads to asymmetric particle shapes which in turn can cause cross-streamline migration, even in the Stokes limit (zero Reynolds number, Re = 0) where one would naively expect time reversibility. The situation becomes even more interesting when the Reynolds number is not zero and inertial effects are taken into account. Both deformability and inertia effects can be exploited to focus or sort particles in suitable flow geometries. In this presentation, I will talk about two examples with potentially high relevance for engineering applications: (1) sorting of RBCs by deformability in microfluidic arrays (at nearly zero Re) and (2) inertia-augmented particle focusing (at finite Re). Deterministic lateral displacement (DLD) devices are commonly used to separate cells and particles by taking advantage of their intrinsic properties (e.g. size). DLD has previously been employed to separate blood components, to enrich white blood cells (leukocytes) or to detect parasites in blood. Deformability effects of RBCs are usually either neglected or declared to be detrimental. In order to investigate the behaviour of deformable RBCs in DLD devices, we have performed high resolution computational fluid dynamics simulations. We find that DLD devices can be employed to separate RBCs by deformability, which is, for example, relevant for the detection of malaria-infected cells.
The interplay of inertia and deformability has a substantial impact on the transport of soft particles suspended in a fluid. However, to date a thorough understanding of these systems is still missing and only a limited number of experimental and theoretical studies is available.
Depending on the deformability and strength of inertial effects, inward or outward lateral migration of the particles in a planar Poiseuille flow takes place. In particular, for increasing Reynolds numbers and strongly deformable particles, distinct flow focusing emerges which is accompanied by a non-monotonic behaviour of the apparent suspension viscosity. This effect, which is caused by both single-particle behaviour and particle-particle interactions, may be of relevance for applications of flow focusing or suspension transport.

Bio
After obtaining his physics diploma from Heidelberg University in 2007, Timm Krueger worked together with Fathollah Varnik and Dierk Raabe at the Max-Planck-Institut für Eisenforschung in Dusseldorf where he developed and implemented a code to simulate dense suspensions of deformable red blood cells in complex geometries. Timm received his PhD from Bochum University in 2011. He then applied his code to more general problems during a postdoc year with Jens Harting in Eindhoven. Afterwards he worked with Peter Coveney at UCL. Since then Timm supervises Gary Davies, a PhD student investigating the dynamics of non-spherical particles at fluid-fluid interfaces. Timm left UCL in 2013 after attaining a Chancellor's Fellowship at Edinburgh University where he is currently researching. Beside his ongoing interest in dense suspensions and interface stabilisation techniques, Timm is now also working on strategies to characterise and separate particles in microfluidic devices.

Contact:Dr Yi Sui
Email:y.sui@qmul.ac.uk

Updated by: Jonathon Hills