Page 45 - Nanotechnology an introduction

Figure 4.7 Sketch of a typical scanning electron micrograph of two amphibole asbestos needles within the pleural cavity occupied by several macrophages. Reproduced with permission from [128].
Although most attention is focused on the potential dangers of manufactured nano-objects inhaled, ingested or adsorbed through the skin, two other
sources may be of greater significance. One is wear of implanted prostheses such as hip replacements, which generates micro- amd
nanoparticles in abundance (e.g., Figure 4.8). The other is the environment, which contains both natural nanoparticles such as the ultrafine
component of desert sand, salt aerosols produced by the evaporation of sea spray and volcanic ash, and artificial but unintentionally produced
aerial nanoparticles such as the products of combustion.

Figure 4.8 Scanning electron micrograph of CoCr particles within tissues adjacent to a human implant, retrieved at revision surgery. Reproduced with permission from [148].
Note that our planet has an oxidizing atmosphere, and has had one probably for at least 2000 million years. This implies that most metals, other
than gold, platinum and so forth (the noble metals), will be oxidized. Hence, many kinds of metallic nanoparticles will not be stable in nature.
A key issue is whether our human defence mechanisms can adapt to cope with new nano-objects emanating from the nanotechnology industry. It
seems that they cannot in the case of long insoluble fibers (e.g., amphibole asbestos and carbon nanotubes). In the case of other nano-objects
such as smoke and mineral particles the dose (concentration, duration, intermittency, etc.) and accompanying lifestyle seem to play a primordial
role.

Although a great deal of work has been (for a review see, e.g., [148]) and continues to be done on the biological effects of nano-objects, the
present effort seems both uncoordinated (with much duplication of effort worldwide alongside the persistent presence of significant gaps in
knowledge) and misguided. Firm general principles as adumbrated above already seem to have been established, and there is no real need to
verify them ad nauseam by testing every conceivable variant of nano-object. Such tests are easy to do at a basic level (the typical procedure
seems to be: introduce a vast quantity of nano-objects into the test species, observe behavior, physiological variables, etc., and finally establish in
which cells or tissues the nano-objects were accumulated, if not excreted). To arrive at meaningful results, however, far more attention needs to be
paid to chronic exposure under realistic conditions. Furthermore, given that we already know that the occurrence of tumors traceable to exposure to
nano-objects typically manifests itself after a delay of several decades, tests need to be long-term. The increasingly dominant mode of funding
scientific research in the developed world, namely project grants lasting for two or three years, is not conducive to the careful, in-depth studies that
are required to achieve real advances in understanding (neither in nanotoxicology nor, it may be remarked, in other fields of scientific endeavor);
rather, this mode encourages superficial, pedestrian work with easily foreseen outcomes. Hopefully organizations like the National Institutes of
Health in the USA will continue to enable a scientist to devote a lifetime of truly exploratory work to his or her chosen topic.

4.4. Summary
The nano/bio interface comprises three meanings. First is the conceptual one: the “living proof of principle” that nanoscale mechanisms (the
subcellular molecular machinery inside a living cell) exist and can function. Within this meaning there is also an inspirational aspect: living cells are
known to distinguish between natural structures differing from one another at the nanoscale, suggesting that artificial mimics may also be used to
invoke specific living responses. Second is the man–machine interface aspect: how can humans control atomic-scale assembly? Conversely, how
can atomic-scale assembly be scaled up to provide artifacts of human dimensions? Third is the literal physical boundary between a living organism
and a nanomaterial, device or system. This applies both to nanobiotechnology (the application of nanotechnology to biology, e.g., implantable
medical devices) and bionanotechnology (the use of biological molecules in nanodevices, i.e. the topic of Chapter 11). This “bio–physical”
interface has several characteristic scales from the biological viewpoint: organismal, cellular and biomolecular. Each scale is examined,
considering the nano/bio as a special case of the general problem of the bio–nonbio (living–nonliving) interface. Perhaps the most important