Biomedical Engineering Reference
In-Depth Information
2.3.2 Characterization-Related Problems of Toxicological Assessment
As was pointed out before, the size and agglomeration state of an ensem-
ble of anoparticles is a dynamic property and sensitively depends on the
characterization medium. In liquid phase, soluble particles may dissolve
and insoluble particles may dynamically agglomerate or deagglomerate in
accordance to the medium composition and pH value. For most classes of
nanoparticles, there is still insufficient understanding of dissolution and
agglomeration dynamics in biological environments. These complex dynam-
ics are governed by particle composition and, especially, its surface chemis-
try. Surface-chemical groups can form pH-dependent surface charges and
control immobilization of molecules as well as of proteins present in the bio-
logical testing environment.
The characterization of nanoparticles for nanotoxicology, due to the
described observations, requires careful adaptation of measurement con-
ditions. The physicochemical characterization of particle size and surface
charge should be preferably performed
in situ
; that is, directly inside the
biological testing environment. If this is not possible, both setups should
resemble as much as possible in order to be sensitive for the complexity of
nanoparticle-medium interaction. These interactions of medium constitu-
ents and nanoparticles are also far from being fully understood. They may
result in profound new effects that are unknown from testing of chemicals
and can hardly be perceived. Nanoparticles may exhibit new transport prop-
erties through cell membranes or the blood-brain barrier. It is even possible
that the surface of inert particles may act as adsorbent for toxic substances
or nutrients. Soluble nanoparticles may release toxic ions, as this has been
described for silver nanoparticles [17]. This way, nanoparticles may act as
vectors (i.e., transport vehicles), inducing local accumulation or release. With
their large surface-to-volume ratio, surface interactions of functional groups
on nanoparticles introduce an additional degree of complexity to the inter-
action of nanoparticles with biological systems. Their understanding, espe-
cially in environments of complex composition such as cell culture media and
biological systems, will be a scientific challenge for many years to come. Any
significant progress in this field will require interdisciplinary cooperation of
nanotoxicologists together with material scientists, chemists, biologists, and
medicines.
2.4 Strategies for Nanoparticle Characterization
Only comprehensive and reproducible nanomaterial characterization can
provide the basis for a reliable understanding of relations between material
properties and biological effects. However, comprehensive characterization
