Biomedical Engineering Reference
In-Depth Information
development and proper application of new nanomaterial characterization
techniques is an urgent issue also for another reason: the successes and pros-
pects of nanostructured material developments create new potential sources
of emission of nanoparticles during synthesis, processing, and use. The widely
unknown hazards and generally unquantified emission probabilities of most
of the new nanomaterials must be of great concern to nanotoxicology. This
underlines the importance of reliable nanoparticle characterization techniques
and motivates to review its state in the present chapter.
The spectrum of nanomaterials under contemporary research is very
broad and incoherent. Consequently, the International Organization for
Standardization (ISO) is developing a systematic and hierarchic set of defini-
tions for nanomaterials.* Other sets of nanomaterial definitions have been or
are being developed for various regulatory contexts. As a widely accepted
feature, nanomaterials are composed of or contain discrete structural parts
below 100 nm in one or more spatial dimension: a thin film (nanoplate), a
nanorod or nanotube, or a nanoparticle. Furthermore, with a spatial exten-
sion in-between molecules and extended bulk materials, nanoparticles
†
are
already too complex to be simple objects. Being confronted with a large but
heterogeneous ensemble of single, distinguishable complex objects, the char-
acterization of nanomaterials is a challenge. In contrast to simple molecules,
nanomaterials already possess a multitude of material characteristics. For
instance, even well-synthesized carbon nanotubes, known for their extended
cage structure of-theoretically-high symmetrical perfection, exhibit in real-
life a large number of individual characteristics such as length, diameter, wall
number, chirality, defect density, etc., as depicted in Figure 2.1. Carbon nano-
tubes will serve as a representative example of nanoparticles also in the fol-
lowing sections.
Even determinate closed-cage molecular structures, such as that of C
60
fullerenes or silsesquioxanes, obtain a high degree of complexity if chemical
side-group functionalization is present. Nanostructured bulk materials, such
as nanocomposites containing nanoparticles or nanostructured domains,
exhibit an even higher degree of material complexity. This complexity leads
to an extremely high variability of nanostructured materials, which allows
for synthesis of new, optimized materials. On the other hand, due to the
multitude of material characteristics, comprehensive characterization is a
demanding and painstaking task. It requires involving different advanced
analysis techniques and will be unaffordable in most cases. Therefore,
minimum sets of characterization techniques have to be identified that are
capable of providing the information relevant for material development and
nanotoxicological testing.
*
ISO/TS 27687.
†
Instead of the core term “nano-object” introduced by ISO/TC 229, the term “nanoparticle”
will be used throughout this chapter for nanoplate (2D), nanorod (1D), or nanoparticle (0D)
nano-objects.
