Biomedical Engineering Reference
In-Depth Information
and devices in a complete, functional, and organizational manner to establish one of the various
dimensions in a nanometer scale (i.e., 1 billionth of a meter) (Emerich and Thanos 2003; Sahoo and
Labhasetwar 2003; Williams 2004; Matsudai and Hunt 2005; Moghimi et al. 2005; Shaffer 2005;
Emerich 2005; Chan 2006; Cheng et al. 2006; Yoshikawa et al. 2006). The applications of nano-
technology in medicine and physiology employ materials and devices designed to interact with the
body at subcellular levels with a high degree of specificity. This can be potentially translated into
targeted cellular and tissue-specific clinical applications designed to achieve maximal therapeutic
efficacies with minimal side effects (Sahoo et al. 2007).
The word “nanoparticle” in drug targeting was conceptualized in the late 1960s and early
1970s by Paul Ehrlich, a physician with a great interest in bacteriology and immunology. This field
was given special attention in the years between 1970 and the early 1980s. Further developments
focused on especially interesting improvements, such as nanoparticles for the delivery of drugs
across the blood-brain barrier (BBB) and PEGylated (i.e., poly(ethylene glycol)) nanoparticles with
a prolonged blood circulation time. The first commercial nanoparticle product containing a drug
(Abraxane
TM
, human serum albumin nanoparticles containing paclitaxel) appeared on the market in
the beginning of 2005 (Kreuter 2007).
Nanoparticles are particulate dispersions or solid particles with a size range of 1-1000 nm
(Figure 3.1). The 1-100 nm scale is of a particular interest for biological interfaces. For example, par-
ticles less than 12 nm in diameter may cross the blood-brain barrier (Oberdörster et al. 2004; Sarin
et al. 2008; Sonavane et al. 2008), and objects of 30 nm or less can be endocytosed by cells (Conner
and Schmid 2003). Based on the methods of preparation, different nanoparticulate systems such as
nanoparticles, nanospheres, or nanocapsules can be obtained. Nanocapsules are systems in which the
drug is confined to a cavity surrounded by a unique, polymeric membrane, while nanospheres are
matrix systems in which the drug is physically and uniformly dispersed. In recent years, biodegradable,
polymeric nanoparticles, particularly those coated with hydrophilic polymer such as PEG, have been
used as potential drug delivery devices because of their ability to circulate for a prolonged period of
time; target a particular organ; as carriers of DNA in gene therapy; and their ability to deliver proteins,
peptides, and genes (Langer 2002; Bhadra et al. 2002; Kommareddy et al. 2005; Lee and Kim 2005).
The growth of nanotechnology has led to many nanoparticle-containing consumer products
appearing in our daily lives. The current markets suggest that there are more than a thousand products
or product lines available worldwide based on nanotechnology principles (Rejeski 2009). Moreover,
the presence of nanoparticles in these products has also become more widespread. Therefore, it has
become necessary to evaluate the safety of nanoparticles in terms of their exposure to their makers
and users. Each and every living organism on earth has been exposed to nanometer-sized foreign
particles; we inhale them with every breath, consume them with every drink, and continuously
encounter nanometer-sized entities. The majority of nanoparticles do not cause ill effects and go
unnoticed but, occasionally, an intruder will cause appreciable harm to the organism.
The nanoparticle's effect on human health and environmental conditions remains unclear (Colvin
2003; Maynard et al. 2006; Nel et al. 2006; Helmus 2007). This issue has become highlighted due to a
large number of scientific reports and published studies. It becomes necessary to know the mechanisms
Atoms
Molecules
Proteins
Viruses
Bacteria
Cells
1 A
100 μm
1 nm
10 nm
10 μm
100 nm
1 μm
Nanoparticles
FIGURE 3.1
Scale showing size of nanoparticles compared to biological components and microorganisms.
