  Studies have shown that following exposure to particulate matter, the
ultrafine fraction (< 100 nm) may deposit along the respiratory tract down to
the alveolar region. To assess the effects of nanoparticles in the lungs, it is
essential to address the question of their biophysicochemical interaction with
the different pulmonary environments, including the lung lining fluids and the
epithelia. Here we examine one of these interactive scenarios and study the
role of supported lipid bilayers (SLB) on the fate of 40 nm fluorescent silica
particles towards living cells. We first study the particle phase behavior in
presence of Curosurf, a pulmonary surfactant substitute used in replacement
therapies. It is found that Curosurf vesicles interact strongly with the
nanoparticles, but do not spontaneously form SLBs. To achieve this goal, we use
sonication to reshape the vesicular membranes and induce the lipid fusion
around the particles. Centrifugal sedimentation and electron microscopy are
carried out to determine the optimum coating conditions and layer thickness. We
then explore the impact of surfactant SLBs on the cytotoxic potential and
interactions towards a malignant epithelial cell line. All in vitro assays
indicate that SLBs mitigate the particle toxicity and internalization rates. In
the cytoplasm, the particle localization is also strongly coating dependent. It
is concluded that SLBs profoundly affect cellular interactions and functions in
vitro and could represent an alternative strategy for particle coating. The
current data also shed some light on potential mechanisms pertaining to the
particle or pathogen transport through the air-blood barrier.
