With each year, a new, deadly virus makes headlines. Whether it’s the recent Ebola outbreak, threats of swine or bird flu, or resistant strains of MRSA, the scientific community is often on its heels trying to find new ways to keep people safe from infection. It’s a legitimate concern – Bill Gates recently told Vox that his biggest fear for mankind was the spread of a highly-contagious, highly-fatal disease akin to Spanish flu.
The good news is, medicine and disinfectants aren’t the only ways organizations are able to push back against the spread of disease. There are antimicrobial films capable of deterring or killing deadly pathogens by leveraging nanomaterials with specific properties. Using many of these layers, or particularly thick ones, can get expensive. But new methods can pack the same antimicrobial punch into a single, thin layer for a more cost-effective solution.
Bacteria grow more resistant to antimicrobial techniques
Bill Gates’ fear of a superbug is not unwarranted. Already, methicillin-resistant staphylococcus aureus or MRSA is a common threat in gyms, pools and other public facilities. The bacteria has grown too powerful to treat with such tried-and-true antibacterial agents as penicillin, methicillin and amoxicillin. As a result, healthcare providers have had to come up with new tactics to eliminate the virus from public areas.
These techniques include using hydrogen peroxide, UV radiation and alcohol-based cleaners, among others. But these remedies may also end up becoming ineffective as bacteria evolves. The process of bacterial resistance happens fast in bacteria – the ones that can survive certain remedies quickly pass on their DNA and lead to more robust strains. That’s why the flu needs a new vaccine every season.
However, certain other methods have been around for millennia and have not yet lost their efficacy. Certain metals like copper and silver were the preferred antimicrobial method of Hippocrates in the fourth century B.C., according to the Deccan Herald. Persian rulers used similar techniques to eliminate bacteria from food and water. Thousands of years later, these metals still act as effective antimicrobial agents.
Silver and copper – the dynamic duo in antimicrobial films
Though these two metals remain effective at killing bacteria, the methods in which they’re deployed for these purposes must be carefully managed. Simply releasing silver or copper into the bloodstream could be deadly for humans. Additionally, these particles can be environmental hazards. But there are other less invasive and less toxic ways to leverage these elements’ antimicrobial properties.
One team of researchers from North Carolina State University developed a process through which silver nanoparticles are added to the plant protein lignin, creating a biodegradable, antimicrobial synthesis. In a paper published by Nature, the team described how the polymer lignin can be converted into nanoparticles and combined with silver ions. The new nanoparticles are then coated in polyelectrolytes, which help the nanoparticles attach to pathogenic bacteria. When the bacteria ingests the lignin, the silver ions are released and kill the pathogen.
Because the silver particles are converted to ions, they manifest in bacterial membranes after the lignin is consumed. The team showed that bacteria leach the silver ions into the environment after they die but they have no toxic effect.
“We expect this method to have a broad impact,” said Alexander P. Richter, PhD Candidate and lead author of the paper. By altering the polyelectrolytes used, the team showed how these compounds can be tailored to target specific bacteria. Its low environmental impact also makes it suitable for use for coating products ranging from medical devices to food packaging.
Copper behaves in a similar fashion to silver – it is an antimicrobial agent that can be used in films to kill bacteria. However, copper is also an essential mineral for humans that can help nourish skin, while silver can be toxic.
One company has taken advantage of those properties to license a technology to manufacturers of cosmetics, clothing, medical technologies and other products that could benefit from antimicrobial activity. In addition to limiting the spread of bacteria, these items can also reduce wrinkles and limit the effects of aging thanks to copper’s restorative abilities.
How do metals work against bacteria?
All of these developments are well and good, but what is it about these metals that makes them so effective at killing bacteria? It’s called the oligodynamic effect, which a study from the National College of Kathmandu defines as “the ability of small amounts of heavy metals to exert a lethal effect on bacterial cells.” Silver and copper aren’t the only metals with that ability – zinc, gold, aluminum, mercury and others have similar properties. However, the exact mechanics behind the oligodynamic effect remain murky.
The study suggested metal ions may denature proteins in bacteria by binding to reactive groups. Because cellular proteins are attracted to metal ions, over time the effects of the ions within the cell would ultimately lead to its deactivation. While that is one possible explanation, what is clear is the result. The study found pots made of copper, silver and brass could be used to rid water of dangerous pathogens. It is these same properties that make metal ions a valuable ingredient in antimicrobial films.
It has also been said that only a silver bullet can kill a werewolf, though this theory is as yet untested and may be unrelated. For now.
What is related is that, in the case of antimicrobial films, analytical testing is necessary to determine particle size and distribution. Film layer analysis can reveal important attributes that could contribute to the film’s ability to inactivate bacteria.