Knee-loading modality drives molecular transport in mouse femur

Area of Science:

• Biomechanics
• Bone Physiology
• Molecular Transport

Background:

• Mechanical loading stimulates bone remodeling.
• Load-driven interstitial fluid flow and molecular transport are implicated in bone formation.
• Understanding molecular transport in the lacunocanalicular network is crucial for bone health.

Purpose of the Study:

• To evaluate load-driven molecular transport in the lacunocanalicular network.
• To investigate the effect of mechanical loading on fluid flow and molecular transport in cortical bone.
• To determine if applied loads enhance molecular transport without inducing significant in situ strain.

Main Methods:

• Fluorescence recovery after photobleaching (FRAP) experiments were performed on mouse femur ex vivo.
• Lacunae were stained with uranine (376 Da).
• A novel knee-loading modality applied sinusoidal force (2 Hz) to the distal epiphysis, with FRAP measurements taken in the diaphysis.

Main Results:

• Applied knee loading significantly shortened the fluorescence recovery time constant from 33 ± 9 s (control) to 25 ± 11 s (p = 0.0014).
• The strain at the measurement site (<100 microstrain) was below the threshold for bone remodeling.
• This indicates enhanced molecular transport in response to loading.

Conclusions:

• Mechanical loading applied to the epiphysis enhances molecular transport in the lacunocanalicular network of cortical bone.
• This enhancement occurs without inducing significant in situ strain in the diaphysis.
• The findings support the role of load-driven interstitial fluid flow in bone remodeling.