Recent years have seen an explosion in the number of studies showing the variety of medical applications of nanotechnology and nanomaterials. In this article we have glimpsed just a small cross-section of this vast field. However, across the range, there exist considerable challenges, the greatest of which appear to be how to scale up production of materials and tools, and how to bring down costs and timescales.
But another challenge is how to quickly secure public confidence that this rapidly expanding technology is safe. And so far, it is not clear whether that is being done.
There are those who suggest concerns about nanotechnology may be over-exaggerated. They point to the fact that just because a material is nanosized, it does not mean it is dangerous, indeed nanoparticles have been around since the Earth was born, occurring naturally in volcanic ash and sea-spray, for example. As byproducts of human activity, they have been present since the Stone Age, in smoke and soot.
Of attempts to investigate the safety of nanomaterials, the National Cancer Institute in the US says there are so many nanoparticles naturally present in the environment that they are "often at order-of-magnitude higher levels than the engineered particles being evaluated". In many respects, they point out, "most engineered nanoparticles are far less toxic than household cleaning products, insecticides used on family pets, and over-the-counter dandruff remedies," and that for instance, in their use as carriers of chemotherapeutics in cancer treatment, they are much less toxic than the drugs they carry.
It is perhaps more in the food sector that we have seen some of the greatest expansion of nanomaterials on a commercial level. Although the number of foods that contain nanomaterials is still small, it appears set to change over the next few years as the technology develops. Nanomaterials are already used to lower levels of fat and sugar without altering taste, or to improve packaging to keep food fresher for longer, or to tell consumers if the food is spoiled. They are also being used to increase the bioavailablity of nutrients (for instance in food supplements).
But, there are also concerned parties, who highlight that while the pace of research quickens, and the market for nanomaterials expands, it appears not enough is being done to discover their toxicological consequences.
This was the view of a science and technology committee of the House of Lords of the British Parliament, who in a recent report on nanotechnology and food, raise several concerns about nanomaterials and human health, particularly the risk posed by ingested nanomaterials.
For instance, one area that concerns the committee is the size and exceptional mobility of nanoparticles: they are small enough, if ingested, to penetrate cell membranes of the lining of the gut, with the potential to access the brain and other parts of the body, and even inside the nuclei of cells.
Another is the solubility and persistence of nanomaterials. What happens, for instance, to insoluble nanoparticles? If they can't be broken down and digested or degraded, is there a danger they will accumulate and damage organs? Nanomaterials comprising inorganic metal oxides and metals are thought to be the ones most likely to pose a risk in this area.
Also, because of their high surface area to mass ratio, nanoparticles are highly reactive, and may for instance, trigger as yet unknown chemical reactions, or by bonding with toxins, allow them to enter cells that they would otherwise have no access to.
For instance, with their large surface area, reactivity and electrical charge, nanomaterials create the conditions for what is described as "particle aggregation" due to physical forces and "particle agglomoration" due to chemical forces, so that individual nanoparticles come together to form larger ones. This may lead not only to dramatically larger particles, for instance in the gut and inside cells, but could also result in disaggregation of clumps of nanoparticles, which could radically alter their physicochemical properties and chemical reactivity.
"Such reversible phenomena add to the difficulty in understanding the behaviour and toxicology of nanomaterials," says the committee, whose overall conclusion is that neither Government nor the Research Councils are giving enough priority to researching the safety of nanotechnology, especially "considering the timescale within which products containing nanomaterials may be developed".
They recommend much more research is needed to "ensure that regulatory agencies can effectively assess the safety of products before they are allowed onto the market".
It would appear, therefore, whether actual or perceived, the potential risk that nanotechnology poses to human health must be investigated, and be seen to be investigated. Most nanomaterials, as the NCI suggests, will likely prove to be harmless.
But when a technology advances rapidly, knowledge and communication about its safety needs to keep pace in order for it to benefit, especially if it is also to secure public confidence. We only have to look at what happened, and to some extent is still happening, with genetically modified food to see how that can go badly wrong.