Scanning transmission electron microscopic tomography of cortical bone using Z-contrast imaging

Area of Science:

• Biomineralization
• Bone Ultrastructure
• Materials Science

Background:

• Previous models suggested bone mineral resides outside collagen fibrils.
• The precise location and structure of bone mineral are crucial for its mechanical properties.

Purpose of the Study:

• To confirm the proposed model of bone ultrastructure using advanced imaging techniques.
• To further elucidate the composite structure of bone at the nanoscale.

Main Methods:

• High-angle annular dark-field electron tomography in scanning transmission electron microscopy.
• Analysis of bone sections cut parallel and perpendicular to fibril axes.

Main Results:

• Tomographic images confirm mineral structures are bundles hundreds of nanometers long and 5 nm thick, oriented parallel to collagen fibrils.
• Mineral structures were observed encircling collagen fibrils, with low mineral density detected inside fibrils.
• Sections perpendicular to fibril axes revealed mineralized walls surrounding empty fibril spaces.

Conclusions:

• The findings strongly support the model that the majority of bone mineral is located outside collagen fibrils.
• This detailed ultrastructural understanding is key to comprehending bone's mechanical integrity.
• Advanced electron tomography provides unprecedented resolution for studying biocomposite materials.