Biomedical Engineering Reference
In-Depth Information
much lower doses provided evidence on translocation of these particles through olfactory axonal
transport into the olfactory bundle and other parts of the brain with signs of neuronal effects. Brains
are naturally of special concern due to the sensitivity of this target organ.
19.8 AN ASSESSMENT OF PARTICLE PARAMETERS RELEVANT
FOR BIOLOGICAL ACTION
The unusual physicochemical properties of nanomaterials are attributable to their small size (sur-
face area and size distribution), chemical composition (purity, crystallinity, electronic properties,
etc.), surface structure (surface reactivity, surface groups, inorganic or organic coatings, etc.), solu-
bility, shape, and aggregation. A question is being raised: “Do nanomaterials properties neces-
sitate a new toxicological science?” The main characteristic of nanomaterials is their size in the
transitional zone between individual atoms or molecules. This can modify the physicochemical
properties of the material and increased uptake and interaction with biological tissues [101]. This
combination of effects can generate adverse biological responses in living cells. The increase in
surface area determines the potential number of reactive groups on the particle surface. The shape
of the NPs has been shown to have a pronounced effect on the biological activity. It is reported
that silver NPs undergo shape-dependent interactions with Escherichia coli [102]. In the case of
anatase TiO 2 nanomaterial, it was shown that alteration to a fiber structure of >15 μm created a
highly toxic particle that initiated an inflammatory response by alveolar macrophages and that
length may be an important determinant of nanomaterial biocompatibility [103]. The water-soluble
rosette nanotube structures display low pulmonary toxicity due to their biologically inspired design
and self-assembled architecture. For metal oxide and carbon nanomaterials, the physicochemical
characterization of nanomaterials and their interaction with biological media are essential for reli-
able studies. It was observed that for gold NPs (size 1.5 nm), the surface charge was a major deter-
minant of their action on cellular processes; the charged NPs induce cell death through apoptosis
and neutral NPs leading to necrosis in HaCaT cells [104]. Considering the physicochemical proper-
ties of various nanomaterials and their interactions with the biological environment, the challenges
presented by simple nanoscale materials such as TiO 2 , ZnO, Ag, CNTs, and CeO 2 are now begin-
ning to be appreciated. But these simple materials are merely the vanguard of a new era of complex
materials, where novel and dynamic functionality is engineered into multifaceted substances. If we
are to meet the challenge of ensuring the safe use of this new generation of substances, it is time to
move beyond “nano” toxicology and toward a new toxicology of sophisticated materials. Therefore,
it is evident that physicochemical characteristics of the materials are very important with respect to
the observed biological effects.
Physicochemical properties of engineered NPs are one of the most important factors that regulate
the behavior of engineered NPs in the environment. Engineered NPs are synthesized for a particu-
lar application; therefore, the physicochemical properties of each NP vary considerably. However,
universally agreed and essentially required properties for engineered NPs are chemical composi-
tion, mass, particle number and concentration, surface area concentration, size distribution, specific
surface area, surface charge/zeta potential, stability, solubility, and nature of engineered NPs shell.
Variation in composition, size, or surface composition of engineered NPs, considerably changes
their physicochemical properties. Properties such as solubility, transparency, color, conductivity,
melting points, and catalytic behavior mainly depend on the particle size. Similarly, surface compo-
sition of the engineered NPs affects the dispersibility, optical properties, conductivity, and catalytic
behavior of the particle. Metallic engineered NPs are usually coated with inorganic or organic
compounds or surfactants to maintain their stability as colloidal solutions. Thus, surface properties
of engineered NPs strongly depend on composition of these coatings also.
Furthermore, surface properties of engineered NPs decide their fate in the environment, for
example, formation of colloidal solution or aggregation. In colloidal solution, engineered NPs
remain dispersed and maintain their reactivity and catalytic behavior and thereby easily interact
Search WWH ::




Custom Search