Collagen pre-strain discontinuity at the bone-Cartilage interface.

Area of Science:

• Biophysics
• Biomaterials Science
• Orthopedics

Background:

• The bone-cartilage unit (BCU) is crucial for joint function and is implicated in osteoarthritis (OA).
• Understanding the mechanical properties of the BCU at the ultrastructural level is key to understanding OA.
• Previous research suggested pre-strain decreases with mineralization in collagenous tissues.

Purpose of the Study:

• To investigate the existence and nature of physiological internal strain gradients at the ultrastructural scale within the BCU.
• To explore the relationship between mineralization, collagen fibril pre-strain, and mechanical properties of the BCU.
• To determine the potential role of these ultrastructural mechanical properties in joint health and OA pathogenesis.

Main Methods:

• Utilized X-ray scattering to probe the axial periodicity of the D-stagger in collagen fibrils.
• Measured microscopic pre-strain in the extracellular matrix (ECM) constituents of the BCU.
• Analyzed strain gradients within the calcified portion of the BCU.

Main Results:

• Identified a physiological internal strain gradient across the BCU at the collagen fibril level.
• Found mineralized collagen nanofibrils in the calcified plate exhibit tensile pre-strain relative to trabecular bone.
• Observed a finer-scale gradient of increasing fibrillar pre-strain within the calcified BCU.

Conclusions:

• The findings challenge the traditional view of pre-strain behavior during mineralization in collagenous tissues.
• The observed pre-strain gradient may confer enhanced molecular resilience and damage resistance to the BCU under physiological compression.
• Disruptions in these molecular-level pre-strains during bone-cartilage interface remodeling could be a factor in osteoarthritis development.