X-ray absorption microtomography (microCT) and small beam diffraction mapping of sea urchin teeth

Area of Science:

• Biomineralization
• Materials Science
• Paleontology

Background:

• Sea urchin teeth are complex biocomposites.
• Understanding their structure is key to their mechanical function.

Purpose of the Study:

• To investigate the internal structure and composition of Lytechinus variegatus teeth using noninvasive X-ray techniques.
• To identify the distribution of mineral and soft tissue components within the teeth.

Main Methods:

• Laboratory X-ray absorption microtomography (microCT) was used to visualize internal structures.
• Synchrotron X-ray diffraction mapping was employed to analyze mineral phase variations and crystal orientation.
• Data from both techniques were correlated to infer soft tissue localization.

Main Results:

• MicroCT identified low attenuation regions, suggesting soft tissue, near the tooth's stone part and along the carinar process-central prism boundary.
• X-ray diffraction revealed highly aligned crystal elements within the tooth structure.
• Two distinct populations of crystal elements with varying magnesium fractions were found in the flange, while the keel showed a single population.
• A band of high protein content (up to 0.25 volume fraction) was detected in the central part of the flange.

Conclusions:

• The study successfully mapped mineral and soft tissue distribution in sea urchin teeth.
• The presence of soft tissue influences the interpretation of microCT data.
• Combined microCT and microdiffraction data are essential for understanding the mechanical properties of biocomposites like sea urchin teeth.