The Nanoscale

The term “nano” comes from the Greek word “nanos”, which means “extremely small”. When we say nanoscale, we are referring to a size range of 1 to 100 nanometers (nm)—the ideal range for investigating teeny-tiny particles and materials. To give you an idea of how small this is, consider a single human hair. Even one hair is much larger than anything on the nanoscale! A hair’s thickness ranges from 60,000 to 100,000 nm (0.06 to 0.1 mm), and a sheet of paper is ~75,000 nm (0.075 mm) thick. A bacterial cell is 10,000 nm (0.01 mm), a tiny red blood cell is ~7,000 nm (0.007 mm) in diameter, a fungi spore is 500 nm (0.0005 mm) and a virus is just between 20 and 200 nm (0.00002 to 0.0002 mm). Now consider this: the radius of a DNA molecule is only 1 nm!

Nanomaterials, the general name for any material in the nanoscale, can range from 0.7 nm in size, such as graphene and carbon nanotubes, all the way up to 80 nm in the form of nanogold, for example [1]. Does this give you an idea of how small nanomaterials are? Figure 1 shows how big nanomaterials are compared to a dog, its tennis ball, a flea, an animal cell, and a bacterial cell.

How are Nanomaterials Changing the World?

Because nanomaterials are so small, they have special properties. Figure 2 shows the use of graphene nanomaterials in bulletproof vests, for example. Traditional bulletproof vests are typically made from very strong plastic. Scientists can strengthen these bulletproof vests by adding graphene sheets to the plastic. This is because the graphene sheets are extremely strong but weighs less than a piece of paper. This nanomaterial can absorb the impact of the bullet, so that the person wearing it does not get hurt.

If you think 3D printing is cool, just wait until 4D printing using nanomaterials as tiny building blocks becomes a reality. Regular 3D printers can build awesome toys but imagine if printers could print toys that transform after printing! That is 4D printing—it uses nanomaterials that change shape under different conditions. Scientists design these nanomaterials to react to heat, light, or water, so they can transform for various uses. Imagine clothes that get warmer when you are cold! 4D printing is new, but it has the potential to do amazing things, especially in medicine. Imagine new bandages that changes color to let you know that your body is not healing properly or can alert you to replace the bandage for a new one. Or imagine tiny robots that help you heal from an injury [2, 3].

Nanomaterials have several other uses in medicine, too. For instance, doctors could treat diseases using nano-sized medicines that can reach sick cells in locations that regular medicines cannot get to. Even certain cancers can be treated with tiny nanodrugs that deliver medicine right to the specific part of the body where it is needed [4].

Nanomaterials can also play an important role in vaccines, especially in some COVID-19 vaccines [5]. These vaccines contain nano-sized bubbles called liposomes. Scientists can put pieces of the virus (or even instructions telling your body to make its own defenses) inside these liposomes. The liposomes protect the vaccine parts as they travel into your body, and they help the vaccine to get to the right cells to trigger protection. This can make the vaccine more effective and require fewer doses. So, next time you get a vaccine, especially for COVID-19, there is a good chance tiny nanomaterials are helping keep you healthy! Using powerful microscopes, we can “see” nanomaterials and how they interact directly with human cells (Figure 3A).

Nanomaterials can also help clean up pollution in water, making our world a healthier place. Finally, as nanomaterials are becoming more common, they can even be found in some packaged snacks. They are usually part of the packaging, used to make it stronger, or they can even be used as an ingredient of the snack itself, to keep it fresher or even to fight off bacteria [7]. This is an area that is still being researched, so scientists are figuring out the best ways to use nanomaterials safely.

How Do Nanomaterials Enter the Human Body?

Nanomaterials typically enter the human body in three ways. First, they can enter through the skin. The skin normally functions as a shield, but it cannot prevent the entry of nanomaterials that are found in some sunscreens, for example. Second, if nanomaterials are inhaled, they can enter through the respiratory system [8]. Due to their small size, the body cannot expel them. Currently, scientists are not exactly sure how bad it is for humans to inhale nanomaterials in the long term, but experiments in the laboratory have shown that nanomaterials in the lungs can be very bad—some can even lead to permanent tissue damage. Finally, nanomaterials can enter through the digestive system, when people eat foods containing these materials as additives like colorants or preservatives.

Does the Human Body Defend Itself Against Nanomaterials?

The human body has many defenses against foreign bodies, such as the mucous membranes in the respiratory and digestive tracts, which trap foreign substances, and the acidity (low pH) of the stomach. In an acidic environment, many types of invaders are killed or dissolved. With nanomaterials, this does not always work. In fact, nanomaterials can bind with normal proteins present in the stomach, creating new structures called biocoronas. Biocoronas can pass through the body unnoticed, as if wearing an invisibility cloak. Therefore, the body’s cells specialize in recognizing and killing foreign invaders do not detect the nanomaterials and thus do not attack them.

What are the Negative Consequences of Nanomaterials in the Body?

The negative effects that nanomaterials can have on the human body are known as nanotoxicity. In some cases, cells recognize nanomaterials as dangerous and attempt to eliminate them through inflammation. Inflammation may produce toxic by-products which, under normal conditions, do not do much damage. However, if there is lots of inflammation or if it lasts a long time, these toxic by-products can damage the body’s cells or even cause them to die through a process called oxidative stress. Imagine your body is a playground, and the toxic byproducts of inflammation are like little troublemakers bouncing around. Normally, your body has “playground monitors” called antioxidants that grab these troublemakers before they cause any damage. But if there are too many troublemakers and not enough monitors, things can get out of control! That is kind of like what happens during oxidative stress, which can then lead to even more inflammation, in a vicious cycle (Figure 3B) [3]. Some nanomaterials cannot be removed or destroyed and remain in the body for years. Continuous inflammation may also lead to tumors over time.

Conclusion

Nanomaterials offer exciting possibilities, from medical treatments to pollution clean-up. However, their small size presents a double-edged sword. While it gives them special properties, it also allows them to bypass the body’s natural defenses, which if out of control can cause inflammation and even cell death. As research into nanomaterials continues, so too must our understanding of their possible risks. By weighing up the potential risk and amazing benefits we can ensure a future where nanotechnology continues to improve our lives without affecting our health.

Glossary

Nanomaterials: ↑ These are very tiny materials, so small you cannot even see them with the naked eye.

Liposomes: ↑ Tiny bubble-like structures that are made of fat and that carry medicine inside them.

Biocorona: ↑ The structure created when molecules from the body, such as proteins, stick to the surface of a non-biological substance, such as nanomaterials, basically disguising them.

Nanotoxicity: ↑ This is when nanomaterials can cause harm to living things (people, animals and the environment). Scientists are still learning about this.

Inflammation: ↑ The body’s reaction to infections and injuries, often appearing as redness and swelling. Too much or long-lasting inflammation can cause cells to die through oxidative stress.

Oxidative Stress: ↑ A process that happens when harmful molecules produced by inflammation damage cells. It can lead to diseases and aging. The body has natural defenses to help protect against it.

Conflict of Interest

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Acknowledgments

The financial assistance provided from the National Research Fund of South Africa is hereby acknowledged. The work/study is based on the research supported wholly by the National Research Foundation of South Africa. We acknowledge that any opinions, findings, and conclusions or recommendations expressed in this article generated by the NRF supported research, are those of the authors and are not necessarily attributed to the NRF. The NRF accepts no liability whatsoever in this regard.