Dental News - Dentist-led study on pearls could produce fracture-resistant materials

Dental Tribune International

Thu. 5. October 2017

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NEW YORK, USA: The beauty of the pearl has captivated people for generations. While it is known more for its value and fashion status, a team of dentists from the New York University College of Dentistry (NYU Dentistry) has now discovered that, beneath its iridescent surface, lies a resilient structure. Around 1,000 times tougher than pure calcium carbonate, the pearl is one of the most robust and lightweight materials found in a living organism.

A byproduct of an oyster’s defense mechanism, the pearl is formed in response to injury to the mantle tissue by an irritant—such as a parasite or grain of sand. Detached cells fall into the inner tissue, where they multiply and form an enclosed saclike structure to seal off the damaged remnants. This cavity is then filled with matrix proteins, followed by minerals, and eventually the pearl is created.

While it is known that this stunning product of nature is made of 95 percent calcium carbonate and 5 percent organic matrix, the role of the proteins modulating their organization has, until recently, been unclear. According to the researchers, this knowledge may advance the understanding of underlying molecular mechanisms of pearl formation and in that way also aid in the development of fracture-resistant materials. These could have a variety of applications, including in the manufacture of improved dental implants, in aerospace and in energy transmission.

Speaking to Dental Tribune International, Dr. Gaurav Jain, a postdoctoral associate at NYU Dentistry and the study’s lead author, said: “Our lab is interested in understanding fracture resistance and toughening properties of the nacre layer of the oyster pearl. To this end, we have been working with a full suite of nacre-specific proteins that nucleate and organize the deposition of mineral crystals within the nacre. These proteins get incorporated within the crystals and create nanoporosities, making the resulting crystal lighter and fracture-resistant. Our goal is to use the bottom-up approach and study these model proteins such that new design principles for durable dental composites and bone repair materials will emerge.”

The formation process of Pinctada fucata, the Japanese pearl oyster used in the culture of pearls, is mediated by a 12-member protein family known as pinctada fucata mantle gene, or PFMG. PFMG1 and PFMG2 are part of this PFMG proteome, which forms the pearl and participates in the formation and repair of the shell. Using the recombinant versions of PFGM1 and PFMG2, the researchers used several characterization techniques to study the behavior of proteins and crystals under various conditions mimicking ocean water.

They found that PFMG1 and PFMG2 combine to form a hydrogel, within which each protein plays a specific role. PFMG2 determines the size of the hydrogel assemblies and regulates the internal structure of the protein films, whereas PFMG1 enhances the stability of tiny ionic clusters that combine to form calcium carbonate layers of pearl.

This study, titled “Functional prioritization and hydrogel regulation phenomena created by a combinatorial pearl-associated two-protein biomineralization model system,” was published in the Biochemistry journal on June 26.