Age and Gender Effects on Strain Response and Biomechanical Performance of C57BL/6 Mice

Abstract

Osteoporosis is a systemic skeletal disease resulting in low bone mass and micro architectural deterioration of bone tissue. It causes a consequent increase in bone fragility and susceptibility to fracture. This age-related bone loss is a major healthcare problem nowadays. Due to this fact, ability to maintain the quality of bone with aging has become an area of interest. C57Bl/6 mice have been commonly used in various studies to investigate the changes in a bone with aging. In this study, C57Bl/6 mice were divided into three age groups: 6 months old, 12 months old and 22 months old. Each age group consisted of 6-7 males and 6-7 female mice. Axial compression tests, three-point bending tests and micro-CT were used to assess age related changes in femurs, tibiae and ulnae. The strain response with aging on tibiae and ulnae was captured using digital image correlation (DIC) technique and strain gaging method. The ulna becomes stiffer compared to the tibia as the mice age and it could be because of a trabecular component which induces flexibility in tibia. The biomechanical performance of femurs, ulnae and tibiae were determined in C57Bl/6 mice. Femurs, tibiae and ulnae of all the groups of mice were analyzed using micro-CT and three-point bending. We calculated the ultimate load to failure (UL), elastic stiffness (ES), modulus of elasticity (E) and the moment of inertia about bending axis (MOI) for each bone. Linear regression models with robust standard errors were used to determine differences in all the parameters with age in each bone and sex. Micro-CT scans of all the bones were analyzed to determine cortical bone volume per tissue volume (BV/TV), trabecular bone volume per tissue volume (BV/TV) and cortical bone area (B.Ar) and tested for correlation with the biomechanical parameters. The significance level was set to p < 0.05. In conclusion, aging effects on the skeleton need to be evaluated in a site-specific fashion and global conclusions extrapolated from one bone to another may not be valid. Significant differences between sexes occur across aging in bone.