WHAT CAN WE LEARN FROM PLANT LEAVES?

Most leaves are quite waterproof. Their outer surface is covered in a waxy cuticle. A cuticle is a coating made of many layers of different biological materials. These materials are mostly hydrophobic. Hydrophobic materials repel water.

The main function of the waxy cuticle is to prevent water movement into or out of the leaf. It is important to prevent water loss from the plant as the water contained in the plant leaves is essential for photosynthesis to continue. Photosynthesis is how plants convert sunlight into energy.

ULTRA-HYDROPHOBIC LEAVES

Many plants have ultra-hydrophobic surfaces. Ultra-hydrophobic leaves repel water even more than normal leaves. They have a specialised surface that has extremely small bumps, called papillae. Papillae are not visible to the naked eye. These form small air pockets that water can float on, above the surface of the leaf. They also make it easier for water to roll off. This effect is called the Lotus Effect, as it was discovered in Lotus leaves.

The Lotus Effect also makes plants self-cleaning. This means dirt, as well as water, is removed from the surface of the plant. This is because water droplets attract dirt to them. The dirt-containing water droplets then roll off the plant. Any dirt on the surface of the leaf blocks sunlight from reaching the leaf. When dirt is removed, more sunlight can reach the leaf to make energy.  

The Lotus Effect is also a way for the plant to protect itself from microscopic lifeforms called pathogens. Pathogens cause disease. Examples of pathogens include viruses and bacteria.  Pathogens will be cleaned from the surface in the same way that dirt is.

Other ultra-hydrophobic surfaces include some insect wings.

SYNTHETIC ULTRA-HYDROPHOBIC MATERIALS

The self-cleaning and non-stick nature of ultra-hydrophobic surfaces has inspired the development of synthetic self-cleaning materials. These materials mimic the microscopic structure of leaf surfaces.

Superhydrophobic coatings that can be applied to various objects are the most common synthetic self-cleaning substances. 

These substances are more environmentally friendly than Teflon and PTFE that are currently used as non-stick coatings. They are toxic and can accumulate in nature.

Possible applications for self-cleaning coatings:

• Non-stick frying pans
•  Self-cleaning solar panels
• In toilets to avoid disease transmission via pathogens on the surface

This is one of the many examples of nature inspiring human technological advances. Often the solutions nature has found to problems are better than those that humans find. Nature may know best!