Biomedical Engineering Reference
In-Depth Information
Although nanostructured implant materials may have many potential advan-
tages in the context of bone tissue engineering, it is important to remember that
studies on nanophase materials have only just begun; there are still many other
issues regarding health that must be answered. Most importantly, infl uences of
nanoparticulates on human health are not well understood, whether exposure
occurs through the manufacturing of nanophase materials or through the implan-
tation of nanophase materials. Clearly, detailed studies in this context are re-
quired if nanoparticles are to be used in these systems [129].
Interactions of nanoparticles with biomolecules—such as DNA, RNA or pro-
teins—are also more likely with decreasing particle size. A number of reports on
cellular uptake of micro- and nano- sized particles have been published. Reports
on particle uptake by endothelial cells, pulmonary epithelium, intestinal epithe-
lium, alveolar macrophages, other macrophages, nerve cells and other cells are
available [129]. Further, it is expected that transport of nanoparticles across the
blood-brain barrier (BBB) is possible by either passive diffusion or by carrier-
mediated endocytosis.
Nanoparticles may also become loose through the degradation of implanted
polymeric materials through oxidation and / or hydrolysis which accelerates
exposure of materials [35]. Corrosion of metals once implanted can also cause the
release of nanoparticulates and, thus, contribute to toxicity in biological environ-
ments. Oxidation accelerates the degradation of metals and the release of metal
ions such as Al
3+
, Ni
2+
, Cr
6+
, and Co
2+
.
In addition, nanoparticles can be generated at artifi cial joints where friction
between two surfaces is high. The outcome of micron-sized wear debris on bone
health has been well-studied for several decades. For instance, ultra high-molecular-
weight polyethylene often used as acetabular cups become brittle through
oxidation and, thus, become susceptible to wear. Conventional size wear debris (i.e.,
micron) triggers osteolysis as well as further wearing (third-body wear).
In contrast, the infl uence of nanoparticulate wear debris—or particles in
general—on bone cell health is only just beginning to be understood. It has been
speculated that the effects of nanotubes on lungs are more toxic than quartz dust.
One study also showed that nanometer titania particles (50 nm) and carbon nano-
tubes (20
100 nm) induced morphological changes in neutrophils and decreased
the overall cell survival rate [130].
On the contrary, other studies have also demonstrated increased cell viability
in the presence nanometer, compared with conventional particles [35]. Specifi -
cally, nanophase materials did not stimulate cytotoxicity but even redeemed the
toxic effects observed on osteoblast viability in the presence of conventionally
sized particles. In this study, osteoblast proliferation was not negatively infl uenced
by alumina and titania nanoparticles, whereas conventional particles of the same
chemistry and crystalline phase increased cell death and slowed cell proliferation.
The potential lack of nanoparticle toxicity was also demonstrated on coatings of
pigment-grade titania particles as nanorods and nanodots of titania (
×
50 nm)
which did not result in as much lung infl ammation when compared with larger
particle sizes (>300 nm) [35] .
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