In a new study published in the journal Nature Physics, researchers at B CUBE, the Center for Molecular Bioengineering at the Technical University in Dresden, and the European Synchrotron Radiation Facility (ESRF) in Grenoble describe for the first time how structural defects in the self-assembly of mother-of-pearl attract and neutralize each other. Ultimately this leads to a perfectly periodic structure.
Molluscs build shells to protect their soft tissues from predators. Mother of pearl, which marine organisms use for “building,” has a complex and very regular structure. This makes it an incredibly durable material. Depending on the species, mother-of-pearl can reach tens of centimeters in length. Regardless of size, each mother-of-pearl consists of materials deposited in many separate cells in several different places simultaneously. This highly periodic and homogeneous structure arises from the initial disorder that has not been known until now.
Researchers from Zlotnikov’s group, in collaboration with the European Synchrotron Radiation Laboratory (ESRF) in Grenoble, have examined the internal structure of early and mature mother-of-pearl in great detail. Using synchrotron-based holographic X-ray nanotomography, they were able to record the growth of nacre over time. “Mother of pearl is a fragile structure with organic elements less than 50 nm in size. The ID16A beamline at ESRF has provided us with an unprecedented opportunity to visualize mother-of-pearl in three dimensions, ”explains Igor Zlotnikov, Ph.D., Head of Research Group B CUBE. The combination of electron-dense and high-periodic inorganic platelets with thin and thin organic surfaces makes a complex structure for imaging nacre. Cryo imaging helped us get the resolution we needed.”
Data analysis was quite challenging. The researchers developed a segmentation algorithm using neural networks and trained it to separate different layers of mother-of-pearl. Thus, they were able to trace what happens to structural defects as the mother of pearl grows.
The behavior of structural defects in the growing nacre was unexpected. Defects in the opposite direction of the screw were attracted to each other from great distances. Right-sided and left-sided defects moved through the structure until they met and neutralized each other. These events resulted in synchronization throughout the tissue. Over time, this allowed the structure to develop into a completely correct and defect-free one.
Many different species of animals create periodic structures similar to mother-of-pearl. The researchers believe that the recently discovered mechanism could control the formation of mother-of-pearl and other biogenic structures.