Mother of pearl secrets
USA mother of pearl shells with natural USA pearls (photo: GIA - pearls from Karipearls)
Researchers from Technische Universitaet (TU) Dresden have described for the first time how the structural defects in the material attract and cancel each other out, leading to the assembly of the perfect mother-of-pearl architecture.
Mother-of-pearl, or nacre, is an incredibly strong material which forms in the shell of some molluscs, creating a protective inner layer. Its strength and lustrous appearance arise from its remarkably regular and uniform architecture. Until now, it has not been known how this structure could be built by such a seemingly disorderly process: many cells simultaneously secreting materials at different locations.
“In the very beginning, the layered mineral-organic tissue is full of structural faults that propagate through a number of layers like a helix,” said Dr Igor Zlotnikov, who leads a multidisciplinary group at the Center for Molecular Bioengineering at TU Dresden focused on the interaction between the physics of materials and cellular control.
“The role of these defects in forming such a periodic tissue has never been established. On the other hand, the mature nacre is defect-free, with a regular, uniform structure. How could perfection emerge from such disorder?”
Zlotnikov and his colleagues worked with Grenoble’s European Synchrotron Radiation Facility to explore the internal structure of the nacre in extremely fine detail; this is necessary due to the organic features of nacre being below 50nm in size. The researchers combined synchrotron-based nanotomography (building a nanoscale model of an object using X-rays from various angles) and a segmentation algorithm utilising neural networks in order to observe the growth of nacre in the painter’s mussel from early stages to maturity.
Crucially, this approach allowed them to follow what happens to the structural defects during this process.