- Interactions between polymer brushes and biological objects
- Nano-rheology of confined polymer solutions
- Nano-mechanics of soft thin films
This topic relies on the design and use of polymer brushes (layers made of macromolecules bound by one end to a surface) to tune the interactions between the surface of a solid and biological cells in its vicinity. We have focused on two different situations of interest :
(i) the first one is related to the rheology of blood in the microvascular system : we have investigated the dynamics of red blood cells (RBC) flowing in microchannels coated with synthetic polymer brushes (PhD Thesis of Luca Lanotte). We have studied how the presence of the polymer coating, mimicking the hydrodynamic function of the so-called endothelial surface layer in vivo, affects the flow of RBC, and we have shown that such coatings can indeed modify in a non-trivial way the RBC dynamics and induce flow reductions which semi-quantitatively compare with in vivo measurements.
(ii) our second field of application of polymer brushes is the control of adhesion of mammalian cells on a surface. We have developped a technique allowing to design brushes of poly(N-isopropylacrylamide) (PNIPAM, a thermoresponsive polymer) that exhibit adhesive patterns of well controlled geometry. We have shown that such patterned brushes can be efficiently used to create regular arrays of cells following a given geometric constrain. Moreover we have shown that swelling transition of PNIPAM upon lowering the temperature of the surface below the polymer LCST (Lower Critical Solution Temperature) can be used to apply repulsive forces to the basal cell membrane, inducing thermally-controlled detachment of the cells from the surface.
The rheological properties of ultra-confined liquids down to some molecular layers is the subject of many questions and controversies. We use dynamic Surface Force Measurements to study the nano-rheology of simple and complex liquids at a nano-scale, in the range of some Hz to 300 Hz. By varying the thickness of a liquid film between a sphere and a plane, its bulk and interfacial responses can be disantangle, giving access to the liquid modulus and its friction onto the solid surface (slippage, or non-flowing layer at wall). This work has made the cover of Phys. Rev. Lett.
We have developped an original method to probe the visco-elastic properties of soft materials without contact. We use a squeeze flow to indent the soft layer, and an elasto-hydrodynamic theory to extract its Young Modulus and loss modulus. The soft layer is not modified by the contact with an external probe. We use this method to study polymer brushes, hydrogels and cell mechanics in collaboration with other teams in Liphy, LPS in Orsay, and Prof. Tong in Hong-Kong.