Analyzing the Biological Entity of Nanomaterials - Safety of Nanomaterials along Their Lifecycle - page 76

NTA—typically a cell culture medium containing 10% serum may contain 10 6 to 10 9
particles in the size range from 30 to several hundred nanometers. Of course these
might be cleared before analysis starts via centrifugation or filtration. Yet, they will
quickly form again typically with a time frame of a few hours, and depending on the
dispersion protocol employed, it may not be possible to completely get rid of them.
But as serum particle and nanoparticles, especially when being composed from met-
als or metal oxides, will have different densities, combination of different techniques
such as chromatographic approaches like SEC/GPC with (ultra-)centrifugation could
be helpful or instead one may also apply density gradient centrifugation approaches.
Summing up it should be emphasized that in an experiment the principal approach
(using selected individual particles or serum, which source of serum, diluted or undi-
luted) as well as the techniques need to be chosen carefully on a case-by-case basis
depending on the precise question. The researcher should be aware of the pitfalls as
well as the strengths of each approach, and eventually some of the weaknesses of a
method might not even be problematic at all in a certain type of analysis.

4.3 EXAMPLE/CASE STUDY: NANOMATERIAL INTERACTIONS

WITH BIOLOGICAL FLUIDS IN THE RESPIRATORY TRACT

4.3.1 P hysiologiCal C onsiderations
Inhalation is one of the major routes for unintentional exposure to nanomaterials and
thus deserves special attention in hazard or risk evaluation. Also there is ongoing
research to use aerosol application also for certain types of nanomedicine. The lung
surface is one of the largest epithelial surfaces in the human body (about 70-100 m 2 )
and the largest one that is in direct contact with the surrounding environment (Geiser
and Kreyling 2010). Inhalation of nanomaterial aerosols may occur for consumers
during use of nanoparticles in sprays and also in occupational settings. In occupational
exposure scenarios, higher nanomaterial aerosol concentrations may be reached, and
this can lead to significant accumulation of nanomaterials in the respiratory tract.
The major part of the pulmonary air-blood barrier (i.e., the alveoli) consists of
an ultra-thin epithelial monolayer (down to 0.1 µm), providing in theory a very short
distance to overcome for nanomaterials to translocate to the systemic circulation.
Both local and systemic effects of inhaled nanomaterials need to be considered in
hazard assessment.
Evaluations should be performed under conditions that are closely related to the
physiological situation. This of course includes also a detailed characterization of the
tested nanomaterial in the respective biological fluid. The epithelium of the respira-
tory tract is covered toward the air-side by a continuous liquid layer: the lung lin-
ing fluid. The lung lining fluid is the first biological matter encountered by inhaled
nanomaterials that deposit. Therefore understanding how the nanomaterials interact
with the lung lining fluid is of high relevance for interpreting results from inhalation
toxicity studies. In the conducting airways, the major component of the lung lining
fluid is mucus, a viscoelastic hydrogel, which is mainly composed of water and gly-
coproteins that form a rather thick and proper noncellular barrier on top of epithelial
cells (Sanders et al. 2009; Antunes, Gudis, and Cohen 2009). Nanomaterials that