Why are scientists talking about cicadas and COVID-19?
When you think about cicadas, I’m sure you think about the loud screeching sound that this bug makes on a hot summer’s day. What you probably don’t know is that the cicada’s wings are self-cleaning and excellent at preventing microbial infections.
Well, some scientists from RMIT University in Australia decided to catch these bugs and figure out the secret of their wings. While a Ph.D. student probably spent 4 years of their lives studying the cicada, I am here to bring you the 5-minute version of the most interesting findings.
There are many different strategies animals and plants use to stop infections. Humans have elegant immune systems that spring into action when bacteria or viruses are detected. Some plants, like peppermint, release antimicrobial chemicals that kill bacteria if they have managed to pass through the waxy outer cuticle of the leaf.
Cicada wings have microscopic spikes that literally pierce bacterial cells, skewering them like kebabs.
Both sides of the cicada’s wings are covered in these spikes and extremely deadly to Pseudomonas aeruginosa, which is a bacteria known to be resistant to antibiotics and is associated with serious hospital-acquired infections. This same mechanism would likely be effective against other strains of bacteria and possibly viruses like COVID-19!
Ouch! My hospital room is covered in spikes!
The cicada’s wings gave the scientists an idea. If we could copy the spiked texture of the wings on critical hospital surfaces, we could stop the spread of antibiotic-resistant bacteria before they have a chance to infect the body. The spikes that prevent bacteria from settling on the surface of the wings would also prevent bacteria from growing on hospital surfaces.
As lead scientist Elena Ivanova said in an interview:
“These surfaces will not require any specific treatment requiring chemical agents or antibiotics to be effective.”
Meaning, this is an environmentally-friendly, “green”, approach to the growing problem of antibiotic-resistant bacteria.
One caveat — in some cases, the dead bacteria would still have to be cleaned off the surfaces so that there is not an accumulation of dead cells on the microspikes.
Now, before you go and say: “I’m not staying in a spike-covered hospital room”, rest-assured the spikes are too small to pierce human skin.
You wouldn’t even be able to feel that they are there.
How do you make a micro-spiked surface?
The required density of spikes and patterns necessary will depend on the target application and microbe. There are pros and cons to the different methods that have been commercially attempted.
When carbon atoms are arranged in a single-layer hexagonal pattern, they create one of the strongest materials known to man — graphene. Graphene is gaining popularity in everything from tissue engineering to solar cells.
Since the sheets are incredibly thin with razor-sharp edges, they would easily cut through the bacterial cell walls. Some early studies have shown effectiveness against Escherichia coli, Staphylococcus aureus, and many other dangerous bacteria.
One of the downsides to using graphene right now is the cost. Although strong efforts to decreasing the cost have been made, the current $100/gram cost makes it too expensive for many commercial applications.
The price of titanium, at ~$0.03/gram ($30/kg), is far less than the cost of graphene, which makes it a much more attractive material to make the micro-spiked surface.
Scientists have shown the titanium surface can be etched, creating sharp edges, suitable for killing the bacteria. Another advantage is that bacteria have trouble sticking to titanium-based materials, meaning that the surface wouldn’t have to be cleaned as often to remove the skewered bacteria. The bacteria would just fall off the surface.
Scientists at a company called Sharklet took a different approach, inspired by sharks. A shark’s skin doesn’t have micro-spikes like the cicada’s wings but, they use a micro-diamond pattern to prevent bacteria from sticking to it.
Using the same micro-diamond pattern on plastic sheeting, Sharklet has made catheters and other medical tubes that are less likely to accumulate bacteria on the surface. This means patients have fewer urinary tract infections (UTIs) and other infections.
Although this technology does not kill the bacteria the way that the titanium and graphene technologies do, if the bacteria doesn’t stick to the surface, and can’t form a biofilm, then it is less likely to lead to an infection.
But, will this work for viruses like COVID-19?
Viruses are more than 100x smaller than bacteria, meaning the spikes needed to destroy a virus would need to be much smaller as well. But, scientists in Spain and scientists in Australia think it can be done.
For the first time, in early 2020, these “nano-spikes”(much smaller than “micro-spikes”) were studied for use against respiratory viruses in addition to the bacteria discussed above.
The etching was done on an aluminum alloy to create the spikes (similar to the titanium example). In some cases, the virus’s outer layer was damaged making it unviable (essentially a “dead” virus). In other cases, the virus was trapped in the spikes. Even if the virus is merely trapped, this would help limit the transfer between surfaces.
The trapped viruses can also help scientists collect virus particles to be studied for vaccine development.
Hope for the future
The reality is that the number of antibiotic-resistant bacteria continues to grow and viruses like COVID-19 are a long-term problem. Adding to the complexity, COVID-19 can live on a surface for up to 24 hrs, depending on the material. Whereas, certain bacteria, such as Pseudomonas aeruginosa, can live on the surface for months.
We need new strategies for killing and removing microbes.
Looking to nature for inspiration, like the cicadas and sharks, is a great place to start. I joked in the beginning about the Ph.D. student spending 4+ years studying a bug, but, without the curiosity of these dedicated scientists, the world would be a much grimmer place.