Biomedical Engineering Reference
In-Depth Information
•
What are the parameters regulating the adsorption of proteins, assuming that the synthetic
identity of the nanoparticle corona may greatly interfere in this process?
•
What are the properties of the polysaccharide corona behind the activation or nonactiva-
tion of immune system proteins?
Answering the first question was an issue in estimating the role of the nanoparticle corona in
controlling the interactions between nanoparticles and proteins. Obviously, this role was expected
to differ greatly whether the proteins remained on top of the corona surface or penetrated through
this layer to either remain or be retained in the corona (Figure 18.4a,b) or diffuse across to reach the
nanoparticle's hydrophobic core (Figure 18.4c).
Results from a series of experiments designed to highlight proteins deposit on the surface of
dextran-coated PIBCA nanoparticles led to the conclusion that proteins adsorbed onto the hydro-
phobic core of the nanoparticles (Figure 18.4c) (Vauthier et al., 2009). The obvious consequence
drawn from this observation was that the properties of the corona are fundamental in controlling
the accessibility of proteins to the nanoparticle core surface, hence controlling the whole phenom-
enon of protein deposition. Due to the anchorage of the dextran chains on the nanoparticle's core's
surface, the space available to accommodate proteins adsorbing on the nanoparticle core is also a
function of the corona characteristics. Using a rather small protein, bovine serum albumin (BSA), it
could be shown that the access of proteins to the surface of the nanoparticle core greatly depended
on both the density and conformation of the chains of dextran in the nanoparticle corona. The results
of experiments performed with other proteins suggested that it is also greatly dependent on the pro-
tein's molecular weight, shape, and dimensions. A dense brush of dextran chains leaves spaces for
the adsorption of proteins onto the core surface of nanoparticles of much smaller size than a loose
brush. However, the maximum amount of BSA that can be accommodated on the nanoparticle core
surface is almost equivalent (2.1 ± 0.4 mg/m² for nanoparticles R1 and 2.7 ± 0.2 mg/m² for nanopar-
ticles R2) (Vauthier et al., 2011). This was explained by the rather small size of BSA. Comparing
nanoparticles R1 and A1, the brush conformation of the chains of dextran in the corona of nanopar-
ticles R1 allowed a lower amount of BSA to adsorb on the nanoparticle core than the loop conforma-
tion found on the surface of nanoparticles A1 (maximum amount of BSA adsorbed at the surface of
nanoparticles A1 = 3.2 mg/m²) (Vauthier et al., 2009). Another important observation drawn from
the experiment was that only proteins whose size suits that of the free spaces can adsorb onto the
surface of the hydrophobic core. This is shown on Figure 18.5; nanoparticles with a dense brush of
dextran (R1) adsorbed a majority of low-molecular weight proteins while the other nanoparticles
(A1, A2, and R2) adsorbed larger amounts of immunoglobulin and fibrinogen, which are proteins
with high molecular weights. The type of proteins that adsorbed on the nanoparticle surface can be
selected by modulating both the conformation of the chains of dextran at the nanoparticle surface
(a)
(b)
(c)
FIGURE 18.4
A scheme illustrating the different hypothesis drawn for protein adsorption on the nanopar-
ticles. The particle is illustrated with a white core and a gray corona while the proteins are shown by the black
spots. Adsorption of proteins taking place at the surface of the corona (a), within the polysaccharide corona
(b) or on the surface of the hydrophobic core assuming that the proteins can diffuse across the polysaccha-
ride corona (c). According to the experiments, proteins adsorbed on the surface of the hydrophobic core of
dextran-coated PIBCA nanoparticles (hypothesis C). Considering nanoparticles coated with dextran sulfate
or heparin, protein interactions may occur according to hypothesis A and/or B. (From Vauthier, C., Lindner,
P., and Cabane, B., 2009.
Coll. Surf. B: Biointerfaces
. 69:207-15. With permission.)
