Also known as mother of pearl, nacre has a hierarchically layered structure which gives it excellent structural qualities including high resilience and flexibility. The material is produced naturally by some mollusc species as a self-defence strategy to strengthen their inner shell and protect their soft tissues from foreign bodies. Although synthetic materials similar in appearance and structure to nacre have previously been created, the production methods involved in developing these materials are often unsustainable and involve high-pressure conditions, toxic chemicals and high temperatures. With the aim of producing artificial nacre by an environmentally-friendly process, scientists from the University of Rochester in the United States have developed a unique production method using bacteria.
Using a layering process — similar to how the material is naturally produced — the Rochester-based researchers combined a calcium source, two strains of bacteria and urea (a compound of urine). Combining Sporosarcina pasteurii (a bacterium which has the ability to precipitate calcite), calcium carbonate, and urea, the material initially crystalised and afterwards was placed in a solution of Bacillus licheniformis. After this, the mixture was stationed in an insulator to create the polymer which was then layered until the synthetic nacre was 5 millimetres thick.
Under an electron microscope, the artificial nacre has a similar chemical structure to the natural material and possesses the same resilience and strength. The artificial nacre is also biocompatible, making it suitable for a number of medical applications including implants and artificial bones. Additionally, the material is tougher than plastic, and sustainable, meaning that it could potentially replace polyvinyl chloride-based plastics. The synthetic nacre could also be used in many architectural and civil engineering applications including crack prevention and as a protective coat for erosion control upon buildings.
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