The strongest synthetic materials are often those that intentionally mimic nature.
A natural substance with which scientists wanted to produce synthetic materials is mother-of-pearl, also known as mother-of-pearl. An exceptionally tough, stiff material, produced by some mollusks and serving as an inner shell layer, it also incorporates the outer layer of pearls, which gives them their lustrous shine.
But the unique properties of mother-of-pearl make it an ideal inspiration for the creation of synthetic materials; most methods of making mother-of-pearl are complex and energy-intensive.
Now, a biologist at the University of Rochester has developed a cost-effective and environmentally friendly method of making mother-of-pearl with an innovative component: bacteria. Created by Anne S. Meyer, an Associate Professor of Biology in Rochester, and her colleagues, the artificial mother of pearl is made from organically engineered materials and has the tenacity of natural mother-of-pearl, but is also stiff and surprisingly flexible.
The Method The material used to make the novel material could lead to new applications in medicine, engineering, and even the construction of buildings on the moon.
Impressive mechanical properties
The impressive mechanical properties of natural mother-of-pearl arise from their hierarchical layer structure, which allows energy to be distributed evenly throughout the material. In an article published in Small Meyer and her colleagues describe their method of using two layers of bacteria to replicate these layers. When examining the samples under an electron microscope, the structure produced by the bacteria was layered similarly to mother-of-pearl naturally produced by molluscs.
Although nacre-inspired materials used to be synthetically manufactured, the samples used to make them are usually associated with expensive equipment, extreme temperatures, high-pressure conditions, and toxic chemicals, Meyer says. "Many people who make artificial mother-of-pearl use polymer layers that are only soluble in nonaqueous solutions, an organic solvent, and then at the end of the process they have this huge waste container that needs to be disposed of."
Producing Mother-of-Pearl In Meyer's lab, however, researchers only need to grow bacteria and leave it in a warm place.
From Bacteria to Mother-of-Pearl
To make the artificial mother-of-pearl, Meyer and her team alternately create thin layers of crystallized calcium carbonate – such as cement – and sticky polymer. First, take a glass or plastic lens and place it in a beaker containing the bacteria Sporosarcina pasteurii a calcium source and urea (in the human body, urea is the waste product excreted from the kidneys when urinated). , This combination triggers the crystallization of calcium carbonate. To prepare the polymer layer, place the slide in a solution of bacteria Bacillus licheniformis and then place the beaker in an incubator.
At the moment it takes about a day to build up a shift. about five microns thick, made of calcium carbonate and polymer. Meyer and her team are currently working on coating other materials, such as metal, with mother-of-pearl, and "we're trying out new techniques to make thicker, pearlescent materials faster, and that could be the entire material itself," Meyer says.
Construction of houses on the moon
One of the most advantageous features of the mother-of-pearl produced in Meyer's laboratory is that it is biocompatible. It consists of materials that the human body produces or that humans can eat naturally. This makes the mother-of-pearl ideal for medical applications such as artificial bones and implants, says Meyer. "For example, if you break your arm, you might use a metal needle that needs to be removed after the bone has healed with a second operation – a needle made of our material would be stiff and tough, but you would not have to remove it. "
And although the material is harder and stiffer than most plastics, it's very light, a quality that's particularly useful for transport vehicles such as planes, boats, or rockets, each extra pound of extra fuel. Because no complex instrumentation is required for the production of bacterial mother-of-pearl and protects the nacreous coating from chemical decomposition and weathering, it is useful for civil engineering applications such as crack prevention, protective coatings for erosion control or preservation of cultural artifacts and could be of use in the food industry as a sustainable packaging material ,
Mother-of-pearl could also be an ideal material for building houses on the moon and other planets: the only "ingredients" would be an astronaut and a small tube of bacteria, Meyer says. "The moon has a lot of calcium in the lunar dust, so the calcium is already there, the astronaut brings the bacteria, and the astronaut makes the urea, which is the only other thing needed to make calcium carbonate layers."  Beyond its qualities as an ideal building material, mother-of-pearl is – as every owner of pearl jewelery knows – "very beautiful," says Meyer due to its stacked layers. Each stacked layer has approximately the same wavelength as visible light. When light falls on the mother-of-pearl, "the wavelengths of light interact with these layers of the same height, so that it bounces back in the same wavelength as visible light." While the bacterial nacre does not interact with visible light because the layers are thicker than the natural nacre, it could interact with infrared wavelengths and bounce off the infrared, Meyer says, offering "potentially unique optical properties."
A new way to make synthetic mother-of-pearl
Ewa M. Spiesz et al. Bacterially Produced, Mother-of-Pearl Controlled Composites, Small (2019). DOI: 10.1002 / smll.201805312
Researchers create artificial mother-of-pearl with bacteria (2019, April 23)
retrieved on April 24, 2019
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