This work, in collaboration with Michelin for the fabrication of composite materials, deals with the colloidal stability of the latex of natural rubber (NR). The NR latex is a polydisperse colloidal dispersion of a bio-polymer in an aqueous serum. The particles are stabilized by a complex layer of phospholipids and proteins. This dispersion can be coagulated by a physical way (under shearing), or by a physical-chemicalway (addition of divalent cations or hydrophobic particles). In this thesis, we studied the coagulation of the NR latex by divalent cations with physical-chemical tools (stability diagrams with different cations, aggregation kinetic of particles, rheological measuremments). Then, the surface of NR particles has been characterized by electrophoresis, firstly in the presence surfactants and secondly depending on the particles size. From the results of the first part we suggest that the coagulation with divalent cations is due to a screening effect because of the increase of ionic strength and that divalent cations can bridge the particles together. This allows keeping them in contact. Adhesion between polymer chains near the surface ensures the irrversible cohesion. In a second time, we saw that the adsorption of surfactants changes the particles surface and the coagulation of NR latex with cations. A small difference of surface charge is observed between the biggest and the smallest NR particles. Finally, a similar behavior has been obtained with a synthetic latex in presence of divalent cations. Our results could be used to develop an industrial process based on this coagulation phenomenon.

Lipid nanocapsules (LNCs) and lipid nanoemulsions (LNEs) are biomimetic synthetic nanocarriers. Their in vitro and in vivo performance was evaluated as a function of their size (25, 50 and 100 nm) and the surface PEG chain length. Analysis methods included complement activation test, particle uptake in macrophage and HEK293(beta 3) cells and biodistribution studies with tumor-grafted mice by fluorescence imaging. A particular attention was paid to keep the concentration of each nanocarrier and to the amount of fluorescent dye in comparable conditions between the in vitro and in vivo studies. Under these conditions, no significant differences were found among the three tested particle sizes and the two nanocarrier types. Longer PEG chains on the LNE surface provided better stealth properties, whereas PEG modification on the LNC formulations inhibited the production of stable nanocarriers. Passive accumulation of LNCs and LNEs in different tumor types depended on the degree of tumor vascularization.

Synopsis Dermo-pharmacy and cosmetic industries have utilized nanotechnologies for two decades. Initially proposed as vector systems for encapsulation of actives, they gained interest in increasing cutaneous bioavailability. Here, we assay the benefits of self-assembled nanoemulsions bearing ligands for targeting specific skin cells. Nanoemulsions, small droplets ranging typically from 20nm to 150nm, possess key properties for further use in cosmetics: long-term stability, optical transparency, extended range of textures and versatility. We investigated this nanoemulsion system and show ability to encapsulate a range of cosmetic actives with various physicochemical properties. Furthermore, this nanoemulsion presents a low cytotoxicity and is capable of directly targeting skin cells through simple addition of specific ligand in a one-step production protocol. This is of interest for increasing bioavailability of actives encapsulated into nanoemulsion droplets which may have penetrated the skin barrier to specific skin cell. Taken together, these chemical and in vitro observations suggest follow-up with in vivo models. Resume L'utilisation des nanotechnologies en cosmetique et en dermo-pharmacie a commencee il y a vingt ans. Initialement simples vecteurs pour l'encapsulation d'actifs, de nombreux systemes nanoparticulaires ont ete developpes afin d'ameliorer la biodisponibilte cutanee des actifs. Dans notre etude nous proposons un systeme de nanoemulsion pour le ciblage specifique de certaines cellules cutanees, dont les gouttelettes presentent des ligands auto-assembles en surface. Les nanoemulsions, dont la taille des gouttelettes varie entre 20 et 150nm, offrent de nombreux avantages dans leur utilisation en cosmetique: une stabilite prolongee, une transparence optique, une texture modifiable et une polyvalence d'emploi. Nous avons effectivement demontre la possibilite d'utiliser ces nanoemulsions afin d'encapsuler des actifs ayant des proprietes physicochimiques differentes, sans affecter la stabilite du systeme. De plus, ces nanoemulsions presentent une cytotoxicite minime et sont capables de cibler specifiquement certaines cellules cutanees par simple ajout de ligands specifiques lors de leur production en une etape. Ces nanoemulsions offrent un interet majeur dans l'amelioration de la biodisponibilite des actifs encapsules en concentrant les gouttelettes ayant traversees la barriere cutanee sur les cellules cibles. Les caracteristiques physico-chimiques ainsi que les observations in vitro realisees dans cette etude encouragent a tester ces nanoemulsions sur modele in vivo.

The incorporation of mineral particles into a polymer matrix leads to extra properties of the polymeric material that are linked to the homogeneity of the mixture. A fine homogeneity can be obtained by using a latex route where the two components are first dispersed in water and then dried. Here, we show a novel way to make an elastomeric composite material via a bulk destabilization of a binary colloidal dispersion. The mixture is composed of a natural rubber latex, which is naturally stabilized, and carbon black particles that are dispersed in water with the help of surfactants. We observe either a transition towards a weak gel, which is a reversible state, or a transition towards an irreversible elastic solid. These structural transitions are mainly controlled by the surfactant concentration that tunes the interaction between natural rubber and carbon black particles, the latter bridging polymer droplets together. We also show that the weak gel can become an irreversible elastic solid under a high shear. This shearinduced heteroaggregation phenomenon exhibits the features of a thermally activated process.