Biomedical Engineering Reference
In-Depth Information
aspect ratio is expressed as (
a
/
), where
a
,
b
, and
c
are the three dimen-
sions of a particle and
a
is the longest side.
An engineered nanoparticle is defined as an intentionally produced parti-
cle that has at least one dimension from 1 to 100 nm. However, the toxicologi-
cal aspects of “nonbulk” materials may emerge from the intrinsic properties
such as surface energy and generation of ROS rather than the extrinsic prop-
erty (size) of nanoparticles [29]. Many toxicological studies suggest that once
the toxicological effects are normalized by specific surface area, no signifi-
cant size-dependent effects would be observed. However, real size-dependent
differences are expected in inorganic nanoparticles between <30 nm and
>30 nm particles because of “nano-effects” [29].
The theoretical relation between N and S assuming a particle is cuboidal is
calculated by Equation 8.4 and the result is shown in Figure 8.3.
3
3
NN
N
−−
(
2
)
S
=
(8.4)
3
where
S
= ratio of surface atoms to total atoms
N
= number of atom on one dimension
Thus, the surface of a nanoparticle is exposed to the biological environ-
ment very efficiently compared with that of a larger particle.
1
0.8
0.6
0.4
0.2
0
0.14
19.6
56
126
252
392
532
672
812
952
6.3
Size (nm)
FIGURE 8.3
Rate of surface to total iron atoms (atomic diameter = 0.14 nm) assuming that iron particle is cubic.
