  Lipid-based drug delivery systems are considered as promising vehicles for
hydrophobic drug compounds. Lipid distribution within the droplet can affect
drug loading capacity in these carriers. It is extremely challenging to
determine the nanostructure within these carriers through the implementation of
the direct experimental methods due to the ultrafine size. Therefore, coarse
grained molecular dynamics (MD) simulation was utilized to model different
lipid-based nanoparticles of the diameter about 12 nm including solid lipid
nanoparticles (SLN), nanoemulsion (NE), and nanostructured lipid carriers
(NLC), and the organization of the lipids within the carriers was explored. The
aforementioned nanoparticles consisted of stearic acid, oleic acid as lipids,
and sodium dodecyl sulfate (SDS) as a surfactant in water medium. Furthermore,
the impact of solid to liquid mass ratio on the lipid distribution within the
lipid matrix was investigated regarding the NLC simulations. We observed the
vesicle-like structure for all the investigated systems in which the
hydrophilic moieties of the lipids and surfactant organized a semi-bilayer fold
into the droplet and the hydrophobic tails accumulated among them. It is worth
mentioning although SDS as a harsh surfactant, which is a special case, was
expected to be present in the surface of the droplet, it penetrated into the
lipids. Our results showed remarkable entrapped water beads inside the droplet
in the form of one or more cavities along the internal layer of the head groups
which was surrounded by lipid head groups. It was also reported that in the
building structure of the nanoemulsion and SLN, in the central parts of the
droplets, lipids were denser than the case of NLCs. Our results indicated that,
in the case of NLC simulations, the lipid distribution within the lipid matrix
was insensitive to the mass fraction of solid to liquid lipids.
