Biomedical Engineering Reference
In-Depth Information
liposomes, micelles, and other types of nano-assemblies [
11
-
13
]. Nanoparticles
have a large surface area-to-volume ratio that helps in diffusion process. Use of
nanoparticles can also lead to special properties such as increased heat and chemi-
cal resistance.
For biomedical applications, the size, charge, and surface chemistry of the
nanoparticles are important since they strongly affect both their circulation time
and also their bioavailability within the body. In addition, magnetic properties and
internalization of particles depend strongly on the size of these magnetic particles.
For example, following systemic administration, larger particles with diameters
greater than 200 nm are usually sequestered by the spleen as a result of mechanical
filtration and are eventually removed by the cells of the phagocyte system, resulting
in decreased blood circulation time. On the other hand, smaller particles with
diameters of less than 8 nm are rapidly removed through extravasation and renal
clearance. Particles of 10-100 nm are optimal for subcutaneous injection and
demonstrate the most prolonged blood circulation times. The particles in this size
range are small enough both to evade the reticulo-endothelial system (RES) of the
body and to penetrate the very small capillaries within the body tissues and,
therefore, may offer the most effective distribution in certain tissues. A nanoparticle
has emerged as a promising candidate for the efficient delivery of drugs used in the
treatment of cancer by avoiding the RES, utilizing the enhanced permeability and
retention effect and tumor-specific targeting.
Nanoparticles such as those of the heavy metals, like cadmium selenide, cad-
mium sulfide, lead sulfide, and cadmium telluride are potentially toxic [
14
,
15
]. The
possible mechanisms by which nanoparticles cause toxicity inside cells are
schematically shown in Fig.
2
. They need to be coated or capped with low toxicity
or nontoxic organic molecules or polymers (e.g., PEG) or with inorganic layers
(e.g., ZnS and silica) for most of the biomedical applications. In fact, many
biomedical imaging and detection applications of QDs encapsulated by complex
molecules do not exhibit noticeable toxic effects [
16
]. One report shows that the
tumor cells labeled with QDs survived in circulation and extravasated into tissues
Fig. 2 Possible mechanisms
by which nanoparticles cause
toxicity inside cells.
GSH
glutathione,
GSSG
glutathione disulfide,
MDA
malondialdehyde,
NF
B
nuclear factor kappa B,
Nrf2
nuclear factor-erythroid
2-related factor 2,
ROS
reactive oxygen species
k
