Biomedical Engineering Reference
In-Depth Information
Interior of alveolus
NP
Alveolar cell
Alveolar capillary
FIGURE 20.4
Entry of nanoparticles into alveolar cells and the pulmonary circulation. (From Jasmine
Jia'en Li et al.
Experimental Biology and Medicine
2010;235:1025-33.)
There are three main routes of entry of carbon nanoparticles (CNPs) into the human body. First,
CNPs are inhaled into the body from the atmospheric air via the upper respiratory tract at the
workplace and from the environment, which has become a common event. Second, CNPs enter the
human body by oral ingestion. Third, CNP entry occurs via the dermal route, either by injection into
the dermal layer or by absorption through the pores of the skin, which are mainly mediated by expo-
sure to therapeutic or cosmetic applications. The lungs would be the first line of contact for particles
that gain entry into the body through inhalation and hence the most likely organ for accumulation
and long-term exposure (Figure 20.4).
20.4 PHYSICAL ATTRIBUTE OF CARBON NANOPARTICLES RESPONSIBLE
FOR TOXICITY
Research suggests that the physicochemical properties such as size, shape, charge, and surface
groups of the NPs determine their immunotoxicity. The physical attributes of CNTs such as fiber
shape, length, and the aggregation status influences the immunological responses and their local
deposition in tissues [9]. The shape and length of CNTs can determine the internalization of CNTs
by macrophages and hence the immune response. Shorter CNTs are reported to be less toxic than
the longer CNTs. Shorter-length CNTs when injected subcutaneously in rats were found in the cyto-
sol of the macrophages after 4 weeks, but longer CNTs were found to be free floating and causing
inflammation [10]. This confirms that the toxicity of MWCNTs was length dependent and compara-
ble with that of asbestos toxicity. In a study, abdominal cavities of rats were injected with MWCNTs
and asbestos fibers. After 24 h of exposure, an increased immune response was observed, and after 7
days of exposure, granuloma formation was observed in both cases. The increased immune response
due to MWCNTs exposure was named “frustrated phagocytosis” wherein macrophages were unable
to engulf long CNTs mainly because of their length.
Surface area and surface chemistry also influence the toxicity of a carbon NP. In one study, five
carbon-based materials, graphite, SWCNTs, MWCNTs, active carbon, and carbon black were tested
for their toxicity on fibroblast cells [11,12]. SWCNTs were found to be the most toxic because they
had the lowest surface area. It was found that hydrophobic SWCNTs with low surface area induce
enhanced toxic effects. CNTs influenced extracellular matrix protein signaling that resulted in the
deformation of cell membranes, and displacement of cell organelles finally leading to cell death.
When two NPs have comparable surface area, toxicity depends on their surface chemistry [13]. It was
observed that unrefined SWCNTs were more toxic than the refined SWCNTs. This was because the
