Biomedical Engineering Reference
In-Depth Information
Fig. 3.3
The coatings of NPs change their biodistribution in the body. Uncoated NPs usually are
rapidly recognized by RES and collected in the liver and spleen. PEGylated NPs adsorb less
protein from the biological environment and have a longer circulation in the blood. Some coatings
such as polysorbate attract specific proteins such as apoE which is effective for brain targeting due
to its BBB-crossing property (Adapted from [
21
])
and hence the circulation lifetime of NPs inside the body is enhanced [
2
]. The
decrease of plasma protein adsorption due to PEGylation is different for various
NPs; in a recent study on hexadecylcyanoacrylate NPs, the PEGylated NPs showed
half of the adsorbed protein of bare NPs. It was also concluded that the higher
adsorption of apolipoprotein E on PEGylated NPs is responsible for the passage of
NPs through the blood-brain barrier (BBB) [
20
]. The adsorption of the protein
corona on PEGylated NPs is also governed by the molecular weight (MW), chain
length, and surface density of PEG on the surface of NPs. Gref et al. [
21
] reported
an increase in the protein adsorption by decreasing the MW or decreasing the
surface density of PEG on three different NPs, poly(lactic acid), poly(lactic-co-
glycolic acid), and poly(o-caprolactone) NPs. However, the relationship between
protein adsorption and the MW or surface density is not linear. The maximum
reduction in protein adsorption occurred at MW of 5,000 and PEG content of
2-5 %. They also noticed that by increasing the MW of PEG, cellular uptake was
decreased and hence the circulation lifetime increased. It should be noted that PEG
cannot prevent adsorption of protein completely, and still some proteins such as
albumin, IgG, apoA-I, and apoE will attach to the NP but with lower concentration.
Price et al. [
22
] reported an inverse relationship between PEG coating of
negatively charged phosphatidic acid liposomes and purified fibrinogen adsorption,
