Nanomaterials: addressing the challenges, benefiting from the opportunities
Some of the deepest challenges we will face in the coming decades derive from the opportunities offered by emerging technological advances. Many of these will improve our quality of life, and develop our economies, but all will be measured against the overarching principle that we do not make some error, and harm ourselves and our environment by exposure to new forms of hazard. Scientific and technological progress has increased both the duration and quality of our lives, throughout much of our history, but by virtue of previous mistakes we have learned to value innovation balanced with caution and safety.
The capacity to create features of the scale of one thousand times smaller than a millimetre (a nanometer) now offers the promise of radical technological development. After a slow start, one can begin to see the pace of real development and outcomes quicken. Some of this is reflected in the papers selected here.
Engineering at the nanoscale already improves the efficiency of clean energy harvesting and storage, lowering our dependence on polluting fossil fuels. It improves the efficiency of energy converted from sunlight, as well as the capacity and safety of batteries. As this develops we will see the different impacts, from faster, smaller and more energy efficient computers and mobile phones, to a new era of the environmentally clean electric car.
Several articles in this Thematic Issue illustrate how nanotechnology is likely to further revolutionise that arena, for example in capturing sunlight and turning it into usable electrical energy. The article ‘Solar cell efficiency boosted with pine tree-like nanotube needle’, describes how light collected from the sun can be bounced around many times inside a nanostructure to improve the chance of it exciting electrons, and ‘Nanotechnology cuts costs and improves efficiency of photovoltaic cells’ shows how electrons that are released can be captured by the large surface area of ‘nano-tree like’ anodes. Together these ensure that more of the sunlight is transformed to captured electrons and electrical power. The article ‘New energy-efficient manufacture of perovskite solar cells’ goes further, and suggests that the existing titanium dioxide that is currently used in solar cells could be replaced by perovskites, yielding quite dramatic improvements in energy conversion, at low device fabrication costs. The article ‘Pomegranate-inspired battery design doubles stored energy’ shows another interesting example suggesting that with nano-engineering the space around anodes will prolong the life, and safety, of batteries. The efficiencies and improvements implied by these examples are sufficient to illustrate how the design and engineering of structures on the nanometre scale could change markets, and make a better, cleaner and safer environment.
Few doubt that the advent of compact and cheap 3D printing, in which nanoparticle ‘inks’ are merged together by heat or light to form solid structures, will change our world. One will see much of what was produced in a factory, from furniture and decoration to the very structures of homes themselves, becoming personalised, individually designed, and made in small companies, or at home. Many of the new ‘inks’ necessary for metallic, ceramic and polymeric composites will be novel nanoparticles. Furthermore, the article ‘New 3D printing technique for environmental nanodevices’ is a good example of how processes also, such as the old-fashioned spinning mill from the previous century, are being transformed into an inexpensive and fast desk-top nano-scale 3D fabrication process.
The article ‘New quantum dot process could lead to super-efficient light-producing technology’ describes how anisotropic (elongated, non-spherical) indium-gallenium nitride quantum dots, or proximity to an anisotropic surface, can lead quantum dots to emit polarised light, potentially enabling 3D television screens, optical computers and other applications, at much lower cost. ‘The potential of new building block-like nanomaterials: van der Waals heterostructures’ and ‘Graphene’s health effects summarised in new guide’ touch on the possibility of engineering ‘building block-crystals’ by arranging different 2D nanostructures such as graphene into low dimension crystals, which allows us, for example, to lower the loss of energy in transmitting electricity. There are also quite novel directions underpinning ‘green nanochemistry' — illustrated by the potential of silk-based electronbeam resists (in the article ‘Making nano-scale manufacturing ecofriendly with silk’) — to be eco-friendly, and have new functionalities.
The article ‘Low energy water purification enabled by nanomaterialcoated sponges’ reports on structures at the nanoscale (a ‘nanosponge’), capable of focusing an applied electric field to more readily puncture the membranes of bacteria that have contaminated water. The article is intriguing not just because of the science, but because it illustrates the point that nanotechnology can make disinfection both safer and less damaging to the environment.
However diverse, all the articles share a common theme – the key enabling properties are a result of the manipulation of structure at the nanoscale.
European institutions and organisations have been at the forefront of efforts to ensure safe and practical implementation of nanotechnology. Significant efforts have been made to address knowledge gaps through research, the financing of responsible innovation, and the upgrading of the regulatory framework to render it capable of addressing the new challenges. There are solid reasons for institutional attention to the issues. Succinctly put, the passing around and modification of natural nanoparticles and macromolecules (for example, proteins) within our bodies is the foundation of much of life. In doing so we regulate and send signals between cells and organs. It is therefore appropriate that questions should be asked about engineered nanoparticles and how they interact with us, and whether they could lead to unforeseen hazards. Those are substantive issues, and answering them well will support the creative drive towards real innovation for many decades to come, and honour our commitments to future generations.
History understood lights the path to the future, so it is worth pausing to understand how we reached this point, and reflect on two key lessons.
Progressive and incremental product development in industry required colloidal particles, one thousand times smaller than a millimetre, to be made even smaller. Thus did, almost accidently and imperceptibly, the evolution of nano-particles driven by product optimisation merge with the growing flood of highly innovative nanomaterials research. Thereby the concept of nanosafety in its broader context becomes almost synonymous with the safety of the evolved (and smaller) ‘legacy’ materials, many of them long in use. The future will view this accidental convergence as a temporary confusion in what nanotechnology is, and what it will become. Succinctly put, the recent past, derived mostly from experience with legacy materials, will not be a good guide to the future. This is well illustrated by the papers presented here, that go far beyond optimisation, and hint at changing markets.
A second set of confusions will also prove to be transient. The initial excitement about nano-innovation also stimulated unfocused fears of widespread ‘nano-hazards’, and these, combined with early poorly framed toxicological studies, left policymakers alert but with bewildering advice. These confusions are being resolved, at least partially. In fact, extensive experimental data now suggest that (most) nanomaterials in current use possess an acute toxicity no greater than might be expected from their bulk counterparts. Those that are toxic (or ‘poisonous’ in this acute sense) are easily identified, sometimes deriving their toxicity from being soluble.
There remain substantive longer-term questions to be understood in this arena of nanosafety, and it will be well to focus the energy, talent and resources on those.
Firstly, some may bioaccumulate, and their final degradation, fate and impact on the animate and inanimate environment is a key question yet to be extensively investigated. Secondly, we have only begun to see the range and variety of materials that will one day enter markets. Indeed, history will barely notice the role of existing colloidal materials made smaller. All our knowledge and experience suggests (and the current papers hint) that it is really novel nano-structural objects (potentially even of similar materials) that, in future, will constitute a nano-enabled technology market. Within the plethora of what is to come, there could exist the potential for novel hazards, both acute and long-term. We will need to guard against that.
Thus, it is worth stressing that nanostructures of a single material with different shapes and geometry may have very different properties. Look at Figure 1 below. Even a single simple material (gold in this case) can be made into an enormous variety of sizes, shapes, topologies, surface modifications and other aspects. The resulting nano-objects (as illustrated also by some of the papers in this collection) may have different electronic, optical, chemical reactivity, and many other properties. This is good news, for it reinforces just how much room there is for the technology to grow. Still, it illustrates the challenge for those studying the safety implications.
One way of focusing the research is along the lines of likely value chains, defining which particular manifestations of the materials are most likely to enter the market. One way of approaching the whole issue then, is to survey key recent scientific outputs to identify those nanomaterials with the highest potential, possibly disruptive application in technology, and support their safe implementation. A concrete example worth thinking about in understanding how research in nanosafety is conceived is suggested in the article ‘Ultrafine particles emitted by commercial desktop 3D printers’. Many common processes where two materials rub against each other release dusts (including ‘nano-dusts’) and our lungs have evolved to deal with this very effectively. As expected, the process of 3D printing itself will release billions of nanoscale particles per minute, and when not managed these may be inhaled into the lungs. Furthermore, the process of forming the ink may involve sufficient heat or other energy such that the surface of the inks may not be as simple as one expects. Ensuring we have clear understanding of the real-life impact of such new dusts, which might differ from (say) domestic nanoparticles generated by cooking, will be the basis for the informed and adequate risk management, and safe use of the product.
It will be important for scientists to learn from the recent past. Prudence suggests that we conserve our energy and resources by focusing both on the key unresolved issues from existing nanomaterials, and also on thoughtfully designed scientific studies of new materials to be relevant in realistic usage or exposure scenarios. In that regard, the article ‘Potential health risk from nanosized cellulose crystals’ is significant, for it raises significant and subtle questions about how we think about safety. Cellulose is one of the most abundant biopolymers on earth. Unsurprisingly, nature has discovered the benefits of engineering on the nanoscale in this arena long before us, and therefore many aspects of plants, from structural integrity to fluid transport, involve nanocellulose. Latterly great interest has emerged in the potential to apply nanocellulose as a structural additive in everything from building materials and car parts, to nanoporous filters to improve water quality, and far beyond. Indeed, many have seen this as an ‘ideal’ nanomaterial: ‘natural’, biodegradable, and ultimately without long-term effects on our environment in much the same way as fallen trees are ultimately consumed by the environment from which they are born. That these materials could, for example, raise new significant inflammatory effects is therefore surprising, possibly even disappointing. And yet, this is an illustration of just how cautious one has to be in interpreting what are, without doubt, correct scientific data. For example, there could be two competing interpretations of these data on nanocellulose.
The first is that the inflammatory effects observed may be an effect of ‘dust overload’, as the surface areas exposed by such materials, being large, could, if we are exposed to large amounts, adsorb , exhaust and overcome the natural protective biomolecules and processes in our lungs. Such overload is a rule rather than an exception when it comes to dust (and applies in a similar manner to mine dust, industrial processes, such as welding, and fruit waste, as well as bedbugs or sandstorms). Regulation, in particular on occupational safety, effectively handles such difficulties by setting occupational exposure limits. Investigations by the nanosafety community (in distinction to traditional occupational exposure research) into those issues will have limited additional impact. The second interpretation, which would be quite surprising for a natural and biodegradable material such as nanocellulose, is that (for example, due to its shape) there arises an exceptional and persistent pro-inflammatory effect that would require specific regulatory restrictions beyond those typical of (say) comparable dusts. Such discoveries are of capital importance, and the nanosafety scientific community can play a key role there. Where feasible, we should in future make efforts to design scientific investigations to differentiate between these scenarios, and clearly signal to the broader community to which category the outcome belongs.
For scientists working in this arena, the challenge will be more than scientific, but to exercise good judgement, remain unmoved by unfounded fears, certainly to have a clear guiding vision of the key issues, but never to grow so confident as to miss what could be radically new, and potentially critical.
From a policy perspective, one could say that scientific understanding of nanomaterials, and their safety, is rapidly developing, and some aspects (particularly in arenas such as acute toxicity) are essentially clarified. There are still significant unknowns particularly in their long-term fate and impact. Therefore, identifying materials, or better, material properties, that have the potential for adverse long-term effects is clearly a priority. However, there is already sufficient general scientific insight that could be implemented within existing regulatory tools, ensuring that sound contemporary science is applied in generation and interpretation of data for safety.
Also, we have every reason to suppose that practical developments will lead to quite new manifestations of materials, with properties as yet poorly explored. Notably, experience derived from legacy materials may not be a good guide to the future. In particular, the differences between materials, brought about by the manipulation of their shape, structure and surface at nanoscale, and their impact in provoking different biological responses is still being clarified. While the breadth of issues may appear to be daunting there is every reason to suppose that a thorough and deep understanding of the principles is possible. In facilitating responsible uptake of the promising technology, research can further support regulation by identifying likely value chains and supporting thorough understanding of the specific nanomaterial required to drive them.
Still, there is no room for complacency, for we are truly at a scientific frontier, and there may yet be surprises; in safety, failure has a high price. We do not doubt that that nanotechnology truly does have the power to make, and indeed is in the process of, making a better world. And translation into economic benefit, both in terms of making novel products and ensuring that safety, will continue to be a partner. But success will require from innovators, scientists, regulators, policymakers, and all concerned, not just resources, but perhaps even more, depth of thought, commitment, focus and persistence.