Influence of articular cartilage sample geometry on mechanical response and properties using finite element...

Area of Science:

• Biomedical Engineering
• Materials Science
• Orthopedics

Background:

• Mechanical testing of articular cartilage is crucial for understanding joint health and disease.
• High variability in mechanical test results poses challenges for accurate tissue characterization.
• Sample geometry is a significant, often overlooked, factor contributing to this variability.

Purpose of the Study:

• To investigate the influence of sample geometry on the mechanical response of articular cartilage during unconfined compression.
• To quantify how geometric irregularities affect the identification of mechanical properties.
• To assess the impact of accounting for sample-specific geometry on material parameter fitting.

Main Methods:

• In-situ phase-contrast enhanced synchrotron micro-tomography was used to image cartilage samples during unconfined compression (stress relaxation).
• Parametric finite element (FE) models incorporating geometric irregularities were developed using a Design of Experiments approach.
• Material parameters were fitted using multiple segmented, sample-specific FE models simultaneously.

Main Results:

• An average inclined sample surface of 4° decreased reaction forces by 15% compared to an ideal cylinder.
• Fitting sample-specific geometries altered material parameters significantly, ranging from -70% to +159%.
• Initial fibril stiffness and permeability increased by 137% and 159%, respectively, with improved model fit.

Conclusions:

• Minor variations in articular cartilage sample geometry substantially influence mechanical property characterization.
• Geometric irregularities can account for a significant portion of the inter-sample variability observed in mechanical testing.
• Accurate geometric assessment and modeling are essential for reliable cartilage mechanical characterization.