Two different correlations between nanoindentation modulus and mineral content in the bone-cartilage interface

Area of Science:

• Biomaterials Science
• Orthopedic Biomechanics
• Tissue Engineering

Background:

• The zone of calcified cartilage (ZCC) is critical for load transfer between articular cartilage and subchondral bone.
• Understanding the micromechanical properties of ZCC is essential for diagnosing and treating joint diseases.
• Previous studies have not fully elucidated the relationship between mineral content and mechanical properties at the micron level within the ZCC.

Purpose of the Study:

• To determine the micron-level mechanical properties of the ZCC.
• To correlate these mechanical properties with mineral concentration in the ZCC.
• To generate 2D material property maps of the ZCC.

Main Methods:

• Combined nanoindentation for stiffness (E(r)) and hardness (H) measurements.
• Utilized quantitative back-scattered electron imaging (qBEI) for mean calcium concentration (Ca(Mean)) analysis.
• Applied these techniques to the ZCC-subchondral bone junction in human patellae.

Main Results:

• The correlation between local stiffness and mineral content in ZCC differs from that in bone.
• ZCC exhibited lower stiffness and hardness than subchondral bone at similar mineral content.
• ZCC showed a broader range of calcium content variation (1-28 wt%) compared to subchondral bone (16-26 wt%).

Conclusions:

• Micromechanical properties and mineral content variations within the ZCC are distinct from subchondral bone.
• 2D material property maps reveal heterogeneous stiffness bands within the ZCC.
• These findings enhance our understanding of ZCC biomechanics and its role in joint function.