Age-related properties at the microscale affect crack propagation in cortical bone

Area of Science:

• Biomaterials Science
• Computational Biology
• Orthopedic Research

Background:

• Bone fracture risk increases with age due to decreased bone mass and quality.
• Bone quality is influenced by microscale factors like porosity, microstructure, microdamage, and material properties.
• The relationship between these microscale characteristics and fracture behavior in aging bone remains unclear.

Purpose of the Study:

• To computationally analyze the impact of microscale characteristics (porosity, toughness, microstructure) on human cortical bone's mechanical behavior.
• To simulate tensile tests using realistic microstructural geometries derived from microscopy.
• To model crack propagation and deflection along osteon boundaries using the extended finite element method.

Main Methods:

• Simulated tensile tests on realistic human cortical bone microstructures.
• Extended finite element method for crack propagation modeling.
• Interface damage law for cement lines to simulate crack deflection around osteons.

Main Results:

• Increased porosity and impaired material integrity led to straighter crack paths, penetrating osteons.
• Impaired tissue integrity, not just porosity, predicted brittle failure behavior.
• Local porosity had a greater influence on crack path than macroscopic porosity.

Conclusions:

• Age-related changes in cortical bone alter crack paths and mechanical responses.
• Increased porosity alone does not drive damage in aging bone; impaired tissue integrity is crucial for brittle failure.
• Computational modeling provides insights into microscale mechanisms of age-related bone fragility.