Hello, my name is Anne Virginie SALSAC
and I am a reserach assistant scientist at the CNRS,
I am coi-responsible at UTC
for biological flow-structure interactions
with CĂŠcile LEGALLAIS.
Today I am goin to present
a microfluid experiment
to determine the
mechanical properties of microcapsules.
The set up you see here
is composed of a microscope
to which a high speed camera is attached.
which can take 2000 images a second
at its base frequency
and we also have a micro-system
whcih you can imagine here
under the microscope
- just here.
The aim of the micro-system
is to make a suspension
of micro-capsules circulate.
The acpasues are small sized,
you see them end-on here,
and if I shake the device you can imagine
te capsules becoming a suspension
50 microns in size.
The capsules go down a tube,
a micro-tube, of approximately
the same dimension, viz.,
50 microns diameter.
The plunger you see here
sets the suspension
of microcapsules in motion,
inside the microchannel tube.
The camera films at rhe same time
and allows us to observe the
deformed capsules.
Let me just start the pump,
right, now we can observe what happens.
on this monitor screen
initially the capsules
were round but react
to the flow pressure
when forced to go
down a tube of the same dimension
approximately
i.e., circa 50 microns.
The capsule are deformed as
you can see here,
the initially round shape
now looks like a parachute
and the rear of the capsule
is now biconcave.
What we now seek to determine
is to relate the new shape
to the capsule's mechanical properties.
And what we need here is some
image processing techiques .
Through the experiment
we find two forms of information.
The first describes the deformed profile
to flow speed.
We determine the latter comparing two
two successives images
because we know the time between images
and we can therefore deduce flow speed
of the capsules' motion.
The following step wil consist of building
a model, a digital model
along with a data base
carry out an inverse analysis
and identify the mechanical properties.
So, our objective now is to couplle
the deformed capsule shape
- as observed - to their mechanical properties
To proceed, we shall
use the casule profile
speed data.
And use the digital model
we developed.
This digital model is in fact
a code for structural flow interaction
that couples both approaches.
Flow is determined by what is called
frontier integrals
and the solids by finite
element analysis.
We therefore have two parameters
in this study that determine
the shape of the capsule.
The first parameter relates
to the shape profile as a
function of capsule size
and tube size
while the second parameter
whoich we desiognate as the capillary
number is an adimensional number
just like the shape aspect.
Mais le nombre capillaire
will represent the viscocity ratios
pof the elastic forces in
the membrane.
Consequently, the aim will be to find
the capillary number which fits best
the experimental values
for the motion ratio aspect which
we can mesure via the images.
Afterwards, we set up a data base
with a wide series of deformed profiles
for varying values
of the two parameters
and we then draw comparisons
using some optimisation techniques,
we can then search
the data base
that correponds best
to the value measured experimentally.
By superimposing the plots, i.e,
when optimal,
we can deduce the value
of the shear module
whiĂ§ch is the main mechanical
property we seek to determine.
The popssible applications for the project
are numerous.
The technique we have developed
is called inverse analysis
and mechanical characterisation
which allows us to determine
the mechanical propetrties of
very variable objects, difficult
to characterise,
because we are investigating objects
down in the 50 micron range
and there are very few techniques available
to measure mechanical parameters.
Most of these techniques
of metrology
ar not capable of measuring a
a single capsule
whereas our technique allows us
to charcaterise complete populations
on a continuous mode.
Yes, now an application... thereare numerous
industrial applications
since this particular one enable QA
quality control and assessment
when the microcapsules are produced.
And it also enables retrocontrol
and hence fabricaion of capsules
to desired property specifications.
Another application, and this will
will be my final point,
is that our method is universal
and can be implemented in like manner
in cylindical channels,
inasmuch as we have the codes
to carry out the inverse
calculations for a cylindrical tube.
or again for a tube with a
rectangular cross-section,
or square, given that the code
is three-dimensional
and allows us to model
both particle flow and their deformation
in microfluidic tubes.
The technology we have
developed in our laboratory
will enable numerous
applications since the microcapsules
are used in many industrial
applications and sectors
for example, in cosmetics
for agro-foodstuffs, for textiles,
for soap powders
it also proves interesting
fom a biological standpoint
inasmuch as it allows us to
to characterise cells
notably our red blood cells.