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Accueil > Équipes > Matière molle : Organisation, Dynamique et Interfaces > Thèmes de Recherche

Polymers at interfaces

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Interactions between polymer brushes and biological objects
(Lionel BUREAU in coll. with DYFCOM and MOTIV groups at LIPhy)

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.

Structure and reactivity in polydiacetylenes

(Sylvie SPAGNOLI, in coll with INSP and ITODYS labs in Paris)

Diacetylenes (DA) R-C-C-C-C-R’ can be polymerized by UV or gamma irradiation of self assembled DA (crystal, Langmuir-Blodgett film) through a topochemical reaction. Microcrystalline films of the DA 4BCMU (R=R’=(CH2)4-OCONH-CH2-COOC4H9) were polymerized by UV irradiation. A method for determining the absolute polymer content X in films has been developed. In this DA the reaction rate is strongly decreased beyond X 0.3. Existing models fail to fit the kinetics. A model based on quenching of the monomer excited state precursor to initiation by energy transfer to a nearby existing chain is developed and quantitatively fits the kinetics. Such quenching may occur in any diacetylene film. One should not assume that an apparent saturation of the absorbance of a film coresponds to complete polymerization. Most often the polymerization leads to long conjugated blue PDA which can undergo a transition to red PDA under various stimuli (temperature, pressure...). In 4BCMU the amide bands associated to the urethanes in the side groups, which form one-dimensional H-bond linear chains are quite similar to those found in peptides and proteins. The positions and strengths of these absorptions, studied by FTIR, are practically unchanged by polymerization or blue to red color transition. This suggests that the H-bond linear chains are the main constitutive interactions in these crystals, and that the conjugated parts must and do “adapt” to the unchanged H-bond lines. No evidence of side group disordering was observed at the irreversible blue to red transition in polymer crystal as often stated.