The BIOMICS project, financed by the European Space Agency and The CNES (Centre National d’Etudes Spatiales), is a collaboration between MRC and the SPECTRO laboratory from Grenoble. The goal of the project is to study the lift forces that appear on a vesicle close to a wall and under a shear flow. The shear flow is realized in a “couette” cell made of two glass plates with a gap of about 170 µm. The bottom plate of the cell is fixed while the top plate rotates creating a shear flow with shear rates in the range 0.5 – 50 s-1.
On normal gravity, this lift force is compensated by the sedimentation effects and we very quickly observe a saturation of this lift phenomenon. Under microgravity, it is expected to have a competition between the lift forces induced by the two walls of the chamber and vesicles should raise the centre of the channel. Furthermore, when a suspension of vesicles is placed in a shear flow, hydrodynamic interactions between vesicles occur and it is expected to see segregation effects.
The 3D visualization of the vesicle suspension is performed by digital holography. A complex home-made software has been developed to retrieve for each acquired hologram (24 hol/sec) the 3D position of each vesicle with its size and shape (aspect-ratio which quantifies the deformability/deflation of the vesicle).
Two different kind of experiments have been performed to better understand the hydrodynamic lift forces and interactions. The first ones consist in re-suspension of the vesicles. The second ones consist in the establishment of the equilibrium distribution.
ESA PF43 (March 2006)
CNES VP59 (September 2006)
CNES VP65 (October 2007)
ESA PF50 (May 2009)
CNES VIP Flight at the “Salon du Bourget” (June 2009)
ESA PF51 (November 2009)
CNES VP82 (April 2010)
ESA PF87 (May 2011)
CNES VP90 Flight at the “Salon du Bourget” (June 2011)
CNES VP95 (March/April 2012)
Maser 11 (15 May 2008)
Maser 12 (13 February 2012)
During re-suspension experiments, vesicles are sedimented on the bottom wall and the shear flow is applied. Lift forces induced by the shear push vesicles to the centre of the channel where the lift forces of both walls are compensated. Those experiments were made in micro and normal gravity during several parabolic flight campaigns onboard the A300 Zero G of Novespace. Taking benefit of the hyper-gravity phase that occurs before the micro-gravity one, it allows to have a very simple and reproducible way to get a sedimented state before applying the shear when entering the microgravity phase. Those experiments allowed to quantify the lift phenomenon.
Establishment of the equilibrium distribution:
Establishment of the equilibrium distribution
This experiment took place in the MASER 11 sounding rocket flight on the 15th of May 2008. In this case, the vesicle suspension is injected during microgravity (filling thus the whole volume of the chamber) and the shear flow is applied. The vesicle cloud is then reaching the centre of the channel establishing a stationary distribution. The 6 minutes of microgravity (provided by the MASER rocket) allowed to reach the equilibrium for different shear rates (50, 25 and 12.5) of two different samples.