Repelling germs with ‘sharkskin’

If you pet a shark the wrong way, its smooth skin feels like sandpaper. But that roughness has a surprisingly useful property — it can repel some germs. Surfaces with a microscopic pattern of bumps that resemble sharkskin can even ward off nasty “superbugs,” a new study finds. These disease-causing bacteria pose a global health threat because they resist conventional germ-fighting chemicals.

A biotechnology company has been developing the sharkskin-like texture. With its tiny ridges just 3 micrometers tall, the texture feels smooth to the touch. The company, Sharklet Technologies in Aurora, Colo., wants to place the texture on medical equipment and other surfaces that could host germs. It plans to roll out microbe-resistant smartphone covers in November. And similarly textured screen protectors could go on sale in January.

The inventor of the sharkskin texture was Anthony Brennan. He is a materials scientist at the University of Florida in Gainesville. There, he designs new materials and analyzes the properties of existing ones.

Brennan wasn’t initially trying to fight superbugs. Years ago, he got funding from the Office of Naval Research. The U.S. Navy wanted to learn how to keep algae off the hulls of its ships. “We were trying to create a surface that, if an organism came to it, would find it too unstable to attach,” Brennan told Science News for Students.

In 2002, he and a dozen other researchers were out at Pearl Harbor in Hawaii. They were testing panels with various coatings, dipping them into the water and hoping they’d emerge clean. Brennan’s panels came back green with algae. “It was disheartening to say the least,” he recalls.

Just then, Brennan spotted a huge submarine returning to port. Smothered with algae, “it looked like a big ol’ whale,” he thought. Like large boats, whales and other marine animals have “crusty” skin due to the build-up of algae and barnacles. But sharks’ skin stays remarkably clear.

The question was why. “I wonder what their skin is made of,” he thought.

Later, as Brennan was developing ways to improve his panel coatings, another researcher caught a shark and sent Brennan a mold of its skin. Viewed under a microscope, the skin had a pattern of dips and ridges. The pattern looked strikingly similar to one that Brennan’s mathematical analyses suggested might work as an improved coating. So he incorporated the sharkskin pattern onto his test panels. And that cut the buildup of green algae by 85 percent.

Brennan later discovered, somewhat by accident, that this same texture also inhibits the attachment of germs, including those that cause human disease. That led to his founding of Sharklet Technologies in 2007.

New tests have now quantified how well the texture repels germs. Sharkskin-inspired surfaces collect and hold 94 percent fewer bacteria than do smooth surfaces. The bumpy surfaces even perform better than copper, a widely used germ-fighter. Brennan’s team published its findings September 17 in Antimicrobial Resistance & Infection Control.

The new findings are a good example of how researchers can learn useful tips from Mother Nature. Adopting such lessons is known as biomimicry.

How the texture works

For their new tests, the researchers “contaminated” three different types of surfaces — smooth plastic, a bumpy sharkskin-inspired plastic and normal copper. Each had been exposed to a nasty, disease-causing germ. They chose to work with Staphylococcus aureus bacteria. Also known as staph, these germs can cause skin infections, including boils, or worse. The scientists used one strain of the bacterium that antibiotic medicines can kill. They also used a resistant form that is immune to the germ-fighting effects of many drugs. That germ is known as methicillin-resistant Staphylococcus aureus, or MRSA.

The experiments attempt to mimic how germs spread in the real world. Surfaces pick up germs as people cough into their hand and then touch a door handle. Or an infected person might sneeze on a laptop. Or someone could spill a drink after it had touched his mouth.

For the spill test, the researchers submerged a surface into a bacteria-tainted solution for an hour. Then they rinsed and dried it. To mimic sneezing, they loaded bacterial solutions into a paint sprayer to spew a tainted mist. And to simulate a sick person’s touch, the scientists poured bacterial solutions onto pieces of cloth. They then pressed the cloth onto surfaces.

Under all conditions, the bumps on the sharkskin-inspired surface retained far fewer bacteria than did the smooth plastic surface. Copper repelled MRSA nearly as well as the surface with microbumps. However, copper was virtually powerless in repelling the attachment of regular staph germs.

The results show “you don’t have to use a toxic chemical or metal coating to kill bacteria,” says Shravanthi Reddy. “We got the same performance with a [sharkskin] pattern,” she says. A chemical engineer, Reddy is Sharklet’s vice president of research and development and an author of the study. 

Unlike antibiotics and other chemicals, the microbumps do not kill bacteria. Instead, they make it hard for the microbes to latch on. The bacteria are 1 to 3 micrometers in size. The surface ridges are about 2 micrometers apart. The germs simply “can’t establish a good attachment,” Reddy explains.

Even more encouraging: “We have done some testing with viruses and the effect is very similar,” she told Science News for Students.

Jon Otter is a microbiologist at King’s College London in England. He thinks the lack of an active kill mechanism makes the new surface treatment attractive. It avoids the problem of germs developing a resistance to it, he says.

Otter blogs about infection control and is a scientific director at Bioquell, a company that develops superbug-decontamination products. He says that the texture may have a downside. “It doesn’t inactivate bacteria — just prevents buildup,” he notes. Otter suspects it might be safer to combine an active germ-killer with a surface repellent such as the new microridges.

Power Words

algae     Single-celled organisms, once considered plants (they aren’t). As aquatic organisms, they grow in water. Like green plants, they depend on sunlight to make their food.

antibiotic  A germ-killing substance prescribed as a medicine (or sometimes as a feed additive to promote the growth of livestock). It does not work against viruses.

antimicrobial   A substance used to kill or inhibit the growth of microbes. This includes naturally derived chemicals, such as many antibiotic medicines. It also includes synthetic chemical products, such as triclosan and triclocarban. Manufacturers have added some antimicrobials — especially triclosan — to a range of sponges, soaps and other household products to deter the growth of germs.

bacterium (plural bacteria)   A single-celled organism forming one of the three domains of life. These dwell nearly everywhere on Earth, from the bottom of the sea to inside animals.

biomimicry   The creation of new devices or techniques based on those seen in nature.

chemical      A substance formed from two or more atoms that unite (become bonded together) in a fixed proportion and structure. For example, water is a chemical made of two hydrogen atoms bonded to one oxygen atom. Its chemical symbol is H₂O.

chemical engineer  A researcher who uses chemistry to solve problems related to the production of food, fuel, medicines and many other products.

copper  A metallic chemical element in the same family as silver and gold. Because it is a good conductor of electricity, it is widely used in electronic devices.

germ  Any one-celled microorganism, such as a bacterium, fungal species or virus particle. Some germs cause disease. Others can promote the health of higher-order organisms, including birds and mammals. The health effects of most germs, however, remain unknown.

materials science   The study of how the atomic and molecular structure of  a material is related to its overall properties. Materials scientists can design new materials or analyze existing ones. Their analyses of a material’s overall properties (such as density, strength and melting point) can help engineers and other researchers select materials that best suited to a new application.

microbe  Short for microorganism.

microbiology  The study of microorganisms, principally bacteria, fungi and viruses. Scientists who study microbes and the infections they can cause or ways that they can interact with their environment are known as microbiologists.

microorganism  A living thing that is too small to see with the unaided eye, including bacteria, some fungi and many other organisms such as amoebas. Most consist of a single cell.

microscope  An instrument used to view objects, like bacteria, or the single cells of plants or animals, that are too small to be visible to the unaided eye.

microscopic    An adjective for things too small to be seen by the unaided eye. It takes a microscope to view such tiny objects, such as bacteria or other one-celled organisms.

pathogen  An organism that causes disease.

resistance    (as in drug resistance) The reduction in the effectiveness of a drug to cure a disease, usually a microbial infection. (as in disease resistance) The ability of an organism to fight off disease.

shark  A type of predatory fish that has survived in one form or other for hundreds of millions of years. Cartilage, not bone, gives its body structure.

smartphone  A cell (or mobile) phone that can perform a host of functions, including search for information on the Internet.

Staphylococcus aureus    (also known as staph) A species of bacteria that is responsible for a number of serious human infections. It can cause surface abscesses, sometimes called boils. If the germ gets into the bloodstream, where it can be carried throughout the body, it may cause pneumonia and infections of the joints or bones.

superbug   A popular term for a disease-causing germ that can withstand medicines.

toxic  Poisonous or able to harm or kill cells, tissues or whole organisms. The measure of risk posed by such a poison is its toxicity.

virus  Tiny infectious particles consisting of RNA or DNA surrounded by protein. Viruses can reproduce only by injecting their genetic material into the cells of living creatures. Although scientists frequently refer to viruses as live or dead, in fact no virus is truly alive. It doesn’t eat like animals do, or make its own food the way plants do. It must hijack the cellular machinery of a living cell in order to survive.