Dynamic changes of macaque cancellous bone following head-down bed rest

Area of Science:

• Biomechanical Engineering
• Space Physiology
• Materials Science

Background:

• Skeletal unloading during spaceflight leads to bone loss and osteopenia, compromising bone strength.
• Understanding the impact of bone loss on the dynamic mechanical properties of cancellous bone is crucial for astronaut health.

Purpose of the Study:

• To investigate how microgravity-induced bone loss affects the dynamic behavior of cancellous bone.
• To develop a constitutive model for cancellous bone under high strain rate conditions.

Main Methods:

• Simulated microgravity using a 28-day head-down bed rest (HDBR) model in 20 macaques.
• Assessed bone density and mechanical properties using split Hopkinson bar testing and high-speed videography.
• Developed a density-based constitutive equation and estimated parameters for a nonlinear viscoelasticity model.

Main Results:

• Cancellous bone from HDBR macaques showed a 6.03% decrease in Young's modulus compared to controls.
• Dynamic experimental results were used to estimate parameters for the Maxwell nonlinear viscoelasticity material model.

Conclusions:

• The developed model of cancellous bone under high strain rate is valuable for establishing medical tolerance criteria for impact trauma.
• Finite element method calculations can utilize this model to predict injury risks related to bone loss.