Combining the Old With the New: using nanotechnology to enhance ancient medicines

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You walk past a body products store on a weekend shopping trip and are immediately overtaken by fragrance, your nose saturated with floral, sugary and tropical scents. Intrigued by the promise of a candle sale, you venture in, perusing the soaps, mists, and candles. About ten free samples later, you find some products labeled ‘aromatherapy’ — mixtures of lavender boasting soothing effects, eucalyptus for relieving stress, peppermint for focus… the list goes on. These claims have some basis in science: chemicals within these products, called essential oils, not only affect mental aspects of health but are also used as antimicrobials to ward off bacteria and other tiny pests. And these properties can be further enhanced with – you guessed it – nanotechnology!  

Essential oils smell great and have interesting chemical properties (photo by Cosiela B.)

Essential oils are compounds produced by various plants to defend against plant-eating insects and fungi and to attract friendly pollinators. These oils have strong characteristic odors, due in part to their volatility. Volatile compounds have a tendency to evaporate into the air, where they can easily interact with receptors in the nose.1 These oils, dubbed “quinta essential” by Paracelsus von Hohenheim in the sixteenth century,2 have been implemented as natural pharmaceuticals for thousands of years, with known records from ancient Egypt, China and India.3 Today, these compounds are used in various industries, including agriculture, pharmaceuticals, cosmetics, sanitation, and food.  

While I would not recommend the use of essential oils as a replacement for modern medicine (they are not regulated by the U.S. Food and Drug Administration and do not undergo the same rigorous testing required for typical pharmaceuticals,4) current research supports various medicinal properties of some oils. For example, lavender has been shown to influence the central nervous system for a sedative effect, and rosemary helps indigestion through activity in the digestive tract.3

One of the more notable features of some essential oils, including oregano, lavender, basil and peppermint, is that they have antimicrobial properties.5 During a time when bacterial resistance to antibiotics is a major public health concern,6 researchers are especially focused on these properties as an alternative or aid to antibiotics. The antimicrobial properties of essential oils also make them popular in the food industry as a non-synthetic preservative.5

So how do essential oils fight bacteria? While the exact mechanism varies among different bacteria types and essential oils, generally the oils can disrupt the cell membranes of bacteria. Essential oils are hydrophobic and avoid water, an effect that can also be seen when you mix cooking oil and water:

Cooking oil is a very familiar hydrophobic substance – most of the time it does not easily mix with water (image by Victor Blacus)

The cell membranes of bacteria are made of lipids (a large molecular component of oil) and are also hydrophobic. Since “like attracts like,” those membrane lipids attract the molecules of the essential oil.  Once at the membrane, the oil may interact with surface proteins, preventing them from functioning properly. The oils may also squeeze through the membrane, altering the cell’s permeability by damaging it and forming leaks, which may eventually lead to death.5,7

Since essential oils and bacterial cell membranes are both hydrophobic, the essential oil can to disrupt the function of a cell membrane and cause leaks, unlike water which is hydrophilic and cannot go through the membrane. (image by Larissa Davis)

As you may remember, there are two different kinds of bacterial membranes: gram positive and gram negative. Since gram negative bacteria have an extra outer membrane that helps to protect the cell, they are not as susceptible to the effects of essential oils as gram-positive bacteria which do not have an extra outer membrane.5,7

Unfortunately, while essential oils can be effective against bacteria, they are not perfect. They are often sensitive to the environment, and break down when exposed to oxygen, light, moisture and heat, which is not ideal for use in everyday products. Since they are hydrophobic, they also don’t mix well with water-based products. But it turns out that many of these issues can be resolved using nanotechnology.5

One technique is nanoencapsulation. Just like you wear a coat in the winter to protect from the cold and snow, nanoencapsulation coats a nano-sized drop of oil to protect it from its environment. This coat can be made from a variety of materials and prevents exposure and evaporation, increasing the oil’s shelf-life. Hydrophilic coats can also make the water-avoiding oil more likely to interact with water, allowing it to disperse more evenly in some foods, medicines, and other products. The essential oils can even be encapsulated in other antimicrobial materials like silver nanoparticles, which work with the essential oil to enhance its bacteria-fighting power.5

Nanoemulsion can also be used to evenly distribute essential oils. If you put a rock in a jar of water, the rock will stay as a large chunk in the bottom of the jar. However, if you first crush the rock into sand before putting it into the water, it can be easily mixed around. This is the same for oil: a large drop won’t mix into water, but if that drop is blended into nano-sized drops through nanoemulsion, it will disperse throughout the liquid. This technique is popular in food to increase the chance the essential oil will encounter dangerous and troublesome microbes, without changing the color or taste of the product.8 The smaller droplets also allow the oil to come into closer contact with bacterial membranes.5

The rock cannot disperse throughout the water, but the sand can! Nanoemulsified oil is like the sand, while a typical oil drop is the like the rock. (image by Larissa Davis)

Though nanoencapsulation of oil is still new to the food industry, both encapsulated thyme and cinnamon oil have been found to delay the spoilage of refrigerated beef.8 Nanoencapsulation and nanoemulsion have also been implemented by big companies within the cosmetics industry like L’Oréal and Lancôme, for use in skin and hair products.9 The growing number of oil nanoemulsion patents around the world  suggests that essential oil nanotechnology will continue to be developed and implemented.8

So, when you get home from your spending spree and slather on lavender, eucalyptus, and peppermint oil lotion (yes, all three. Life is chaotic and sometimes you need all the help you can get), remember that just because a science is ancient, doesn’t mean that is isn’t worth further investigation and development. Though humans have been taking advantage of essential oils for at least a millennium, research and new technology continues to improve their effectiveness and suit them to our current needs.


EDUCATIONAL RESOURCES


REFERENCES

  1. Bakkali, F. et al. Biological effects of essential oils—A review. Food and Chemical Toxicology. 2008, 46(2):446-475. Doi: 10.1016/j.fct.2007.09.106
  2. Edris, A. E. Pharmaceutical and therapeutic potentials of essential oils and their individual volatile constituents: A review. Phytotherapy Research. 2007, 21:308-323. Doi: 10.1002/ptr.2072
  3. Ali, B.; Al-Wabel, N.A.; Shams, S.; Ahamad, A.; Khan, S.A.; Anwar, F. Essential oils used in aromatherapy: A systemic review. Asian Pacific Journal of Tropical Biomedicine. 2015, 5(8): 601-611. Doi: 10.1016/j.apjtb.2015.05.007
  4. Patrick, Mike. A Doctor’s take on Essential Oils. 700 Children’s Blog. Nationwide Children’s Hospital, June 4, 2015.
  5. Chouhan, S. et al. Antimicrobial activity of some essential oils—Present status and future perspectives. Medicines. 2017, 4(3): 58. Doi: 10.3390/medicines4030058.
  6. U.S Department of Health & Human Services. Centers for Disease Control and Prevention: Antibiotic/Antimicrobial Resistance (AR/AMR). (accessed June 28, 2019)
  7. Nazzaro, F. et al. Effect of Essential Oils on Pathogenic Bacteria. Pharmaceuticals. 2013, 6(12): 1451-1474. Doi: 10.3390/ph6121451
  8. Ferreira,C. & Nunes, I.L. Oil nanoencapsulation: development, application, and incorporation into the food market. Nanoscale Research Letters. 2019, 14(9). Doi: 10.1186/s11671-018-2829-2
  9. Sundari, P.T.; Anushree, H. Eur. J. of Pharm. Med. Res 2017; 4(8):617-627.