Web Release Date: January 10,
Gravity-Driven Microfluidic Particle Sorting Device with Hydrodynamic Separation Amplification
and
Department of Biomedical Engineering, Department of Radiology, and Department of Macromolecular Science and Engineering, University of Michigan, Ann Arbor, Michigan 48109
Received for review August 18, 2006. Accepted November 17, 2006.
Abstract:
This paper describes a simple microfluidic sorting system
that can perform size profiling and continuous mass-dependent separation of particles through combined use
of gravity (1 g) and hydrodynamic flows capable of rapidly
amplifying sedimentation-based separation between particles. Operation of the device relies on two microfluidic
transport processes: (i) initial hydrodynamic focusing of
particles in a microchannel oriented parallel to gravity and
(ii) subsequent sample separation where positional difference between particles with different mass generated
by sedimentation is further amplified by hydrodynamic
flows whose streamlines gradually widen out due to the
geometry of a widening microchannel oriented perpendicular to gravity. The microfluidic sorting device was
fabricated in poly(dimethylsiloxane), and hydrodynamic
flows in microchannels were driven by gravity without
using external pumps. We conducted theoretical and
experimental studies on fluid dynamic characteristics of
laminar flows in widening microchannels and hydrodynamic amplification of particle separation. Direct trajectory monitoring, collection, and postanalysis of separated
particles were performed using polystyrene microbeads
with different sizes to demonstrate rapid (<1 min) and
high-purity (>99.9%) separation. Finally, we demonstrated biomedical applications of our system by isolating
small-sized (diameter <6 
m) perfluorocarbon liquid
droplets from polydisperse droplet emulsions, which is
crucial in preparing contrast agents for safe, reliable
ultrasound medical imaging, tracers for magnetic resonance imaging, or transpulmonary droplets used in ultrasound-based occlusion therapy for cancer treatment.
Our method enables straightforward, rapid, real-time size
monitoring and continuous separation of particles in
simple stand-alone microfabricated devices without the
need for bulky and complex external power sources. We
believe that this system will provide a useful tool to
separate colloids and particles for various analytical and
preparative applications and may hold potential for separation of cells or development of diagnostic tools requiring
point-of-care sample preparation or testing.
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