Biomedical Engineering Reference
In-Depth Information
“by-stander” damage to adjacent host cells, (iii) penetration into the biofilm, (iv) light exposure
time required to kill bacteria within in vivo biofilms, and (v) widespread relatively nonspecific bac-
terial killing
[95]
. The photosensitizer erythrosine has an advantage over other dyes because it is
currently used in dentistry to visualize dental plaque in vivo, and so its lack of toxicity in the host
is well established. For use in periodontitis, the dye needs to be applied subgingivally prior to
fiber-optic laser light activation. However, when disease is present, the periodontal site has a
marked flow of GCF into the pocket, and most photosensitizers lose some activity in the presence
of extraneous protein. Also, some have virtually no effect in the presence of saliva and other body
fluids. This is because the agents complex with proteins and host cells in the GCF and effectively
compete for binding to bacteria. The use of nanoparticles as applied to PDT may help to overcome
some of the issues associated with serum constituents.
10.6
Biocompatibility of nanoparticles within the oral cavity
Although the development and application of nanotechnology are of major importance in both
industrial and consumer areas, knowledge regarding the possible toxicity of nanotechnology pro-
ducts to humans is limited. Whereas it is well known that copper in a non-nanoparticulate form is
actively excreted from the body, non-nanoparticulate silver can accumulate within the body.
However, the threat posed by these metals in a nanoparticulate form is far from clear
[99]
. In order
to understand the mechanism of toxicity, a thorough knowledge of the toxicokinetic properties of
nanoparticles is required. This includes information on the absorption, distribution, metabolism,
and excretion of nanoparticles
[100]
. In theory, certain nanoparticles may be retained within the
body for longer than the desirable time, and thus the safety profile becomes a matter of overriding
significance. Nanomaterials are able to cross biological membranes and access cells, tissues, and
organs that larger-sized particles normally cannot. Nanomaterials can enter the blood stream
following inhalation or ingestion, and some can even penetrate the skin. In vitro studies with lung
epithelial cells, enterocytes, and skin keratinocytes indicate marked differences in susceptibility to
metallic nanoparticles according to cell type tested (R.P. Allaker and M.A. Vargas-Reus, unpub-
lished observations)
However, a particle's surface chemistry, which in some cases can be modified,
can govern whether it should be considered further for biomedical applications
[25]
.
Toxicology and biodynamic studies suggest that silica, silicon, and chitosan nanoparticles are rela-
tively safe if introduced via the oral route
[99]
. Testing of NO-releasing silica nanoparticles (at the
highest concentration tested of 8 mg/mL) with fibroblasts demonstrated that cell proliferation was
inhibited to a lesser degree than with chlorhexidine
[85]
. Likewise, QA-PEI nanoparticles incorpo-
rated into composite resins to restore teeth at 1% w/w demonstrate no additional toxic effects on cul-
tured cells or experimental animal tissue in comparison to unmodified composites
[78]
.In
comparison to other metals, silver is less toxic to human cells and is only ever used at very low con-
centrations in vivo
[27]
. For example, silver nanoparticles have been shown to inhibit Candida spp.
at a concentration of 0.2
.
μ
μ
g/mL, which is markedly less than the concentration (30
g/mL) required
to demonstrate a toxic effect against human fibroblasts
[101]
.
The safe use of nanotechnology and the design of nanomaterials for biological applications,
including the control of oral biofilms, involve a thorough understanding of the interface between
