Recent development of nanotechnologies, while promising great advances, in particular in the bio-medical field, rise several questions, e.g. what is the behaviour of these nano-objects in biological conditions? Among these materials, silica arise special interest for it is already used in cosmetics, with the associated question of dermal exposure, and is studied for intracellular drug delivery. This study aims at bringing some answers concerning the fate of different kind of silica nanoparticles in biological conditions by exploring the following phenomena: aggregation and dissolution in biological media, internalisation in 2D or 3D cell cultures, toxicity and intracellular fate. In the context of cutaneous exposure, human dermal cells were used, both in direct exposition and through diffusion of the nanoparticles in dermis-like collagen matrices immobilizing cells. It appears that dissolution is size-dependant, internalisation is influenced by diameter and composition of the particles, toxic effects are governed by number of exposed particles, more than weight concentration, and intracellular dissolution can be modulated by the size of the particles or incorporation of disulfide moieties, possibly inducing the release of encapsulated molecules. Thus characteristics of the nanoparticles (diameter, surface charge and composition) influence their behaviour in biological media and in presence of cells
