Biomedical Engineering Reference
In-Depth Information
1 microparticle
60 µm diameter
(size of human hair)
(a)
1 million particles
60 nm diameter
1 billion nanoparticles
60 nm diameter
Human hair
(b)
(c)
1400
Bulk melting temperature
1000
1200
Gibbs-Thomson equation
T = T
Tbulk
- C/d
500
1000
0
1
800
10 100
Particle diameter (nm)
1000
1
10
Gold particle diameter, d (nm)
100
1000
FIGURE 9.3
Correlation of size and specific surface area. (a) An illustration of the increase in surface
area with the decrease of surface area. The image of human hair is shown to scale, with a 60 μm diameter
representing the approximate size of human hair. In comparison, the same amount of particles, by mass, but
of a smaller diameter (600 and 60 nm) has a much larger surface area. (b) Graph representing correlation of
particle diameter and surface-area-to-mass ratio. (c) Impact of diameter on melting temperature provides
evidence that physiochemical properties become altered with the change in particle diameter. (Reprinted with
permission from Buzea C, Pacheco, II, Robbie K. Nanomaterials and nanoparticles: Sources and toxicity.
Biointerphases
20 07;2(4):M R17-71.)
in diameter [69,72,73]. However, this may vary based on the targeted cell type and other factors.
Specifically, the ligand is a more important factor in cell uptake, as the rate of uptake depends on the
targeted ligand. Studies have shown that same nanoparticle coated in different protein but targeting
the same receptor has different uptake rates [74].
Depending on the material and the process of synthesis, the nanoparticles may carry a charge.
As the intracellular side of the membrane carries a slightly negative charge, positively charged
nanoparticles uptake more readily, perhaps due to the attraction forces or the types of components
present in the protein corona in the biological system [73-76]. The interactions of the nanoparticles
with the cell membrane on a molecular level are especially important to consider in the assessment
of their health effects. For instance, even very small (2 nm) nanoparticles bearing a positive charge
can perturb the cell membrane potential and may cause the influx of calcium ions (Ca
2+
) into the cell
[77]. As a result, cell proliferation may be inhibited. On the other hand, larger, charged nanoparti-
cles (4-20 nm) may even induce reconstruction of lipid bilayers [78]. Furthermore, interactions with
the cell membrane also differ based on the charge of the nanoparticle, as the binding of negatively
charged nanoparticles induce local gelation, while the binding of positively charge nanoparticles
induces fluidity. However, the surface charge and properties of the nanoparticle may be altered
through interactions with the environment, which include interactions with proteins in serum and
the formation of a corona made up of multiple proteins (Figures 9.4 and 9.5) [68,69,79-81]. In fact,
