Every year, the U.S. military costs billions of dollars dealing with equipment deterioration due to corrosion. It is estimated that about 30-40% of aborted missions directly result from corrosion, specifically those created by microorganisms.
Big Problems From Small Microbes
Generally, corrosion results from the oxidation of most or all atoms on the same metal surface. Meanwhile, there is also a type of corrosion that is caused by the presence of microorganisms. Also known as microbial corrosion, this process can occur in various environments such as freshwater, seawater, sewage, soil, and aircraft petrol.
Two elements are required for microbially induced corrosion to occur: microbes initiating the attack and an environment conducive to their growth and spread. The exact microbes and the resulting damage they cause differ from one material to another, but the most common sources are bacteria.
Utilizing the Potential of Biofilms
Some bacteria form colonies, which can lead to biofilm formation, an assemblage of surface-associated microbial cells that stick to each other and other surfaces. Much of the biofilms research focuses on the hard-to-treat infections they can cause in humans.
It was found that biofilms can damage non-living objects, too. For instance, they can cause pitting in steel as they release hydrogen sulfide during respiration. Other types of biofilm can also erode the inner surface of a fighter jet's fuel tanks. Regarding a ship's hull, biofilms can become a base for seaweed that can increase drag.
Scientists at the Defense Advanced Research Projects Agency (DARPA) thought of working with biofilms instead of fighting them. The American military research outfit decided to replace harmful bacteria with helpful ones, thus turning the problem into its solution. To make this possible, the agency developed the Arcadia program to harness bacteria to create biofilm coatings for military equipment.
Under this program, scientists work with nature to develop probiotics using microbes that naturally occur on military assets. These probiotics are expected to produce robust and beneficial coatings that can prevent corrosion, decrease drag, and inhibit the growth of black mold.
One of the goals of the Arcadia program is to boost the performance of underwater gliders, the small seagoing drones that carry out surveying and anti-submarine missions. Experts utilize the accumulation of biofilms on the hull, which can reduce a glider's speed by up to 90%.
The program also aims to tackle corrosive bacteria in aircraft fuel tanks. DARPA is funding a project called Microbes Achieve Resistance to MicroOrganism-influenced Rust (µarmor) to help find a biofilm to prevent microbial corrosion.
Instead of engineering new microorganisms in the laboratory, the researchers are tasked to find naturally occurring species with beneficial effects. Several candidate species can be screened simultaneously using microfluidics and rapid genetic sequencing technologies. Once the ideal candidate is found, the scientists can either start with a sterile surface and add the microbes or gradually replace an existing ecosystem of harmful bacteria.
Either way, experts hope to develop a spray-on mix that can be applied wherever needed. Since biofilms can grow, they will be much easier to maintain than manufactured coatings.
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