Biomedical Engineering Reference
In-Depth Information
Fig. 4.2
ITC measurements of HSA titration into solution of 70 nm NPs of
N
-isopropyla-
crylamide (NIPAM) to
N
-
tert
-butylacrylamide (BAM) copolymer nanoparticles with ratio of
50:50 on the
left
and 85:15 on the
right
(Adapted from [
1
])
The human serum albumin (HSA)-NPs association is an exothermic reaction.
The highest surface coverage of HSA is achieved for the more hydrophobic
particles. This shows that the surface coverage is strongly dependent on the particle
hydrophobicity. It has been shown also that surface curvature of
N
-isopropyla-
crylamide/
N
-
tert
-butylacrylamide interferes with HSA binding. Indeed the protein
adsorbed on flat surfaces tends to accumulate in multilayers and can form
two-dimensional structures. However, for high curvatures, proteins are far from
each other and tend to form one layer around the NPs [
12
].
Studies show an evident conformational change when lysozyme interacts with
NPs. For example, the lysozyme adsorbed on silver colloids shows a loss in
conformation, and more precisely the Ag NP seems to interact with a tryptophan
and phenylalanine residues [
13
]. ZnO NPs have been reported to modify the
secondary structure of lysozyme [
14
]. The interaction of lysozyme with NPs has
also been described for TiO
2
NPs. Lysozyme seems to form bridges between the
NPs and enhance the formation of aggregates. Indeed the content of
α
-helix
decreased while the content of
-sheet increased, resulting in a loss of activity [
15
].
Cedervall et al. [
1
,
5
] showed that ITC can be used to assess the stoichiometry
and affinity of protein binding. Their measurements are shown in Fig.
4.2
.
β
