Quantification of Age Related Tissue Level Failure Strains of Rat Femoral Cortical Bones Using an Approach Combining Macrocompressive Test and Microfinite Element Analysis

Abstract

Bone mechanical properties vary with age; meanwhile, a close relationship exists among bone mechanical properties at different levels. Therefore, conducting multilevel analyses for bone structures with different ages are necessary to elucidate the effects of aging on bone mechanical properties at different levels. In this study, an approach that combined microfinite element (microFE) analysis and macrocompressive test was established to simulate the failure of male rat femoral cortical bone. MicroFE analyses were primarily performed for rat cortical bones with different ages to simulate their failure processes under compressive load. Tissuelevel failure strains in tension and compression of these cortical bones were then backcalculated by fitting the experimental stress–strain curves. Thus, tissuelevel failure strains of rat femoral cortical bones with different ages were quantified. The tissuelevel failure strain exhibited a biphasic behavior with age: in the period of skeletal maturity (1–7 months of age), the failure strain gradually increased; when the rat exceeded 7 months of age, the failure strain sharply decreased. In the period of skeletal maturity, both the macroand tissuelevels mechanical properties showed a large promotion. In the period of skeletal aging (9–15 months of age), the tissuelevel mechanical properties sharply deteriorated; however, the macromechanical properties only slightly deteriorated. The agerelated changes in tissuelevel failure strain were revealed through the analysis of male rat femoral cortical bones with different ages, which provided a theoretical basis to understand the relationship between rat cortical bone mechanical properties at macroand tissuelevels and decrease of bone strength with age.