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On 20 September 2020, a YSN-ASM Science Café was organised to explore the promise of nanotechnologies and the public fear or rejection it may create.
The novel features of engineered nanomaterials (ENMs) offer enormous potential for technological progress in the 21st century. The advantages of nanoparticles, such as the increased solubility of nanosuspensions and their low production costs have resulted in their rapid commercialisation in various applications, raising concerns regarding their safety for human health and the environment.
With the continued commercial upscaling of engineered nanomaterials production and application, comes a responsibility to understand, reduce and where possible to eradicate, the environmental impacts of these materials.
Shawn Keng moderated this session of Science Café featuring Dr Leo Bey Fen, a senior lecturer and research fellow at the Nanotechnology and Catalysis Research Centre (NANOCAT), Universiti Malaya.
Dr Leo outlined her presentation for the session, which included an introduction to nanomaterials and its applications in consumer products, as well as the benefits and negative impacts associated with it. Another topic that Dr Leo mentioned was nanosafety, covering the primary mechanism of toxicity, the life cycle of products, product regulation as well as risk assessments.
What Are Nanomaterials?
In the International System of Units, the prefix "nano" means one-billionth, or 10-9; therefore, one nanometer is one-billionth of a meter. To help us imagine how small things are on the nanoscale compared to biological components, the diagram below illustrates:
Source: http://www.thepipettepen.com/nanomedicine-how-much-are-we-willing-to-pay/
Next, Dr Leo showed a picture of a home interior, asking viewers to identify which items may contain nanomaterials. Based on the image, nanomaterials may be present in fabric items such as a windbreaker or tablecloth, making them waterproof.
Nanomaterials in circuit boards of laptops and handphones enable them to be lighter and lasts longer on a single charge. Nanomaterials can also make TVs thinner and lighter; printers may utilise inks with nanoparticles that make printed items UV-resistant and water-resistant.
Floors and walls may be coated with a finishing that contains nanoparticles that makes them easier to clean, harder to scratch. Sports equipment can also utilise nanomaterials that make them lighter yet more robust, contributing to sports performance. Nanoparticles such as carbon nanotubes and silica can strengthen tyres such as those on a bicycle.
Other examples of nanomaterial applications are the non-stick zirconium coating on frying pans; flexible displays utilising graphene sheets; zinc oxide and titanium oxide nanoparticles in sunscreens to reflect UV rays; as well as titania nanoparticles that impart a hydrophobic quality on car windshields and rearview mirrors.
Why Nano?
Viewers might ask, why use particles on the nanoscale? Dr Leo used a piece of paper illustrated the answer with a sheet of paper. A sheet of paper has six sides; she tore it apart into smaller pieces, resulting in more surface area. Maintaining the same volume of particles while reducing it to the nanoscale increases its surface area, enabling more reactions to happen more quickly. Properties of materials are also vastly different at the nanoscale compared to larger scales. The benefits of nanomaterials have made it a burgeoning industry, with a global market that is expected to reach USD2.29 billion by 2026.
Nanomaterials' Portals of Entry
Silver is the most commonly used element in nanomaterial production. It can be found mostly in medical and hygiene applications, such as wound dressings, water filters and toothpaste. Dr Leo then brought up the case of Paul Karason. The latter used silver compounds internally and topically for more than ten years to treat his dermatitis, turning his complexion a greyish blue colour. She used Mr Karason's case as an example of how nanoparticles will affect humans in the long run.
According to Dr Leo, there are several portals for nanoparticles to enter the body, how it moves in the body, and how it is excreted from the body. Among the common ways nanoparticles can enter the body are:
Topical creams and clothing, via deposition
Drug delivery, via injections
Air, via inhalation
Food and water, via ingestion
Nanoparticles that come into contact via deposition will enter through the skin; injected nanoparticles will enter the blood circulation; it can also be inhaled from the air, entering the respiratory tract; ingested nanoparticles can go into the gastrointestinal (GI) tract. From these portals of entry, the nanoparticles will go to different organs, such as the kidneys, liver, spleen and heart; it may also go to the central or peripheral nervous systems, lymph nodes, and bone marrow. Then, these nanoparticles will be excreted via sweat/exfoliation, urine, breast milk, or faeces.
What Happens When We Inhale Nanoparticles?
Dr Leo used asbestos as an example to explain her answer to this question. If the particle is at micron size, we can remove most of the particles by coughing; if it is smaller than micron size, the particle can travel deeper into the respiratory system, reaching the alveolar regions. When particles get to this region, these particles can be removed by macrophages (large, specialised cells that recognise, engulf and destroy target cells) only if they are within the 1-3 micrometre size range. Particles smaller than 1 micrometre will not be removed by macrophages and will interact with the lung's epithelial cells or enter the blood circulation.
Then, Dr Leo showed some studies done at NANOCAT to see the interactions between 50-nanometer silver nanoparticles with macrophages. In one hour, the macrophages engulfed some of the nanoparticles. Some nanoparticles have entered the macrophages within 24 hours. Within a week, these silver nanoparticles have entered the nucleus of the macrophages and killed some of these cells. Dr Leo stated that different sizes of nanoparticles were also used; this study showed that nanoparticles showed more toxicity at smaller sizes.
Nanomaterial Design
A nanomaterial scientist can design different nanomaterials by altering its shape, size, material, and surface to exhibit the desired properties.
Altering the shape of a nanomaterial is essential in ensuring the optimum cell uptake and improving the rate of drug delivery, as well as meeting site-specific drug delivery requirements.
Altering the surface of nanoparticles can give them different properties, such as hydrophobicity or hydrophilicity; surface charges; and various functional groups.
Efficacy of nanoparticles can also be influenced by its size, which can be produced between 1 to 100 nanometers via synthesis to meet specific demands. New hybrid materials can also be created by designing nanoparticles to meet various needs.
A report by the Society of Toxicology showed that different physical/chemical properties of nanomaterials would affect its toxicity profile. According to the study, smaller particle sizes exhibit more toxicity. Positively-charged nanomaterials are more toxic due to increased interactions. Different surface coatings will show different toxicity profiles. Varying nanomaterial compositions yield differing ionic dissolution, altering its toxicity profile. It was also discovered that rod- and fibre-shaped nanomaterials have less uptake efficiency but induces substantial damage by inducing higher cytokine production. The secretion of cytokines and chemokines from cells is a fundamental response to injury and infection in the body.
Having said the above, how do the properties of nanoparticles affect its toxicity? Dr Leo explained that it all boils down to how these properties affect the ion release from the nanoparticle and the subsequent production of reactive oxygen species (ROS), which induces oxidative stress. The mechanism of ROS production is yet to be fully understood, but its effects are well-documented.
ROS plays significant physiological roles in cellular signalling systems and induction of mitogenic (cell division) responses. However, overproduction of ROS has several adverse effects. Among the adverse effects include lipid/protein peroxidation (oxidative degeneration), mitochondrial respiratory chain disruption, chromosomal aberration, and DNA damage, which leads to cancer and cardiovascular diseases.
Concerns and Issues Related to Nanotechnology
Some of the concerns related to nanotechnology are lack of public information, leading to misinformation and misunderstandings. This misinformation is further fuelled by a tendency for products to be marketed incorrectly with the "nano" label.
Besides that, there are no nano-specific regulations available for products to come into the market, and there are no standard testing methods for human exposure measurements to nanomaterials. Additionally, the traditional methods of detecting, analysing, and measuring micron-sized materials are ineffective to measure nanoparticles. The dearth of methodologies to conduct risk assessments, toxicological assessments and life cycle analysis of nanomaterial-containing products are also a cause for concern.
Environmental, Health and Safety of Nanomaterials
It is essential to understand the effects of nanomaterials throughout its life cycle to ensure the health and safety of the users and the environment. From the production of raw materials to produce nanomaterials to its subsequent manufacturing of consumer products, care must be exercised by the workers in the production process, as well as the industrial emissions that entail.
Continuing the cycle, consumers must be aware of the presence of nanomaterials in the products they use as well as understanding the effects it has on them. Upon completion of the product's life cycle, products with nanomaterials need to be disposed of responsibly with the safety and health of the workers in mind.
In essence, the life cycle behaviour and potential risks of new technologies must be analysed. Current risk assessment systems must also be modified to make these cater to the unique challenges posed by nanomaterials.