Fluid pressure relaxation depends upon osteonal microstructure: modeling an oscillatory bending experiment

Area of Science:

• Biomedical Engineering
• Mechanobiology
• Skeletal Biology

Background:

• Mechanical loading of bone generates fluid flow, inducing shear stresses on bone cells.
• This fluid flow is hypothesized to be a critical component of bone's mechanosensory system.
• Previous theoretical models simplified bone microstructure, limiting their accuracy.

Purpose of the Study:

• To develop a novel poroelastic model of bone fluid flow.
• To investigate the primary pathways of fluid relaxation in bone under mechanical loading.
• To understand how microstructural details influence fluid pressure and shear stresses on bone cells.

Main Methods:

• Developed a new poroelastic model incorporating lacunar-canalicular porosity, osteonal canals, and cement lines.
• Simulated oscillatory four-point bending experiments on bone specimens.
• Analyzed local fluid pressure profiles and relaxation behaviors based on microstructure and loading frequency.

Main Results:

• Identified two distinct fluid relaxation behaviors: through osteonal canals and across specimen thickness.
• Demonstrated that fluid pressure response is sensitive to loading frequency, not cement line permeability.
• Showed significant amplification of fluid pressure gradients and shear stresses near osteonal canals at higher frequencies.

Conclusions:

• Bone fluid relaxation primarily occurs through the osteonal canal system, especially at higher loading frequencies.
• Microstructural details significantly influence bone fluid flow dynamics and mechanotransduction.
• Higher loading frequencies amplify shear stresses on osteocytes, potentially enhancing mechanosensing.