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Posted: June 25, 2009
Virus filters for medical diagnosis
(Nanowerk News) Providing reliable evidence of viruses in human blood presently requires
time- and labor-intensive molecular-biological procedures. Established
methods are particularly hard pushed to produce evidence
when the viral burden is very low, for example during a phase of therapy.
This could soon change. While developing new types of micropumps
without movable parts, scientists from the Fraunhofer Institute
for Biomedical Engineering IBMT came across an unexpected phenomenon:
stable turbulence structures formed in the microscale pump
channels. The nano- and microparticles actually intended to verify the
pump effect accumulated in large quantities in the channels. The vortex
patterns completely filled the whole microchannel, creating a virtually
100% trap for the particles that followed the generated flow profile,
although there is a very large cross-section to flow through.
“The development of flow vortices is nothing unusual on the macroscopic
scale. However, in microchannels the flow lines almost run in parallel,”
explains Richard Stein from the IBMT. “The question, therefore, was,
how is it possible for vortices to be formed from this which were sufficiently
stable and effective for the concentration of nanoparticles?”
Experiments were not successful in determining the parameters by
which the filter effect could be systematically controlled. This is because
in the pump mechanism examined, high-frequency electrical
traveling waves propel the fluid into the microchannels, superimposing
a large number of effects on one another.
“In order to understand the complex procedures, there was a clear
need for a theoretical description. My task was to describe the surprising
phenomenon and to make it controllable,” reflects Richard Stein.
In his thesis “Mathematical modeling, analysis and numerical simulation
of electrothermally driven micropumps”, Richard Stein succeeded
in explaining the development of the vortex pattern.
To this end, he
had to factor in all the relevant processes – of an electrical, thermal
and hydrodynamic nature – in a three-dimensional model. Mr. Stein
will receive the 1st Hugo Geiger Prize for this paper. The findings contained
in the paper explain the observed effects completely, so that
now both effective micropumps and efficient particle filters can be developed
and built for many biomedical applications.