Orientation and Deformation of HAp Crystals and Elastic Modulus of Single Trabecula in Bovine Femur

Abstract

Cancellous bone has a hierarchical structure, spanning from the trabecular network, the single trabecula, to the hydroxyapatite (HAp) crystals and collagen fibrils level. The mechanical properties in the hierarchical structure may affect the elastic modulus and strength of cancellous bone; however, the relationship has not been elucidated. The differences in these properties between single trabecula and cortical bone have not been fully investigated. The aim of the study was to quantify the orientation and deformation behavior of HAp crystals and the elastic modulus of single trabeculae. In the experiments, single trabecular specimens were taken from the proximal cancellous bone of an adult bovine femur and were air-dried. The specimens were fixed to thin metal jigs, where the gauge length was set to 3 mm. To measure the elastic modulus of the specimens, the tensile tests were conducted using a small tensile testing device under microscopic observation and the deformation was measured using the gauge length. The specimens were irradiated with characteristic Mo-Kα X-rays and diffracted X-rays were detected with an X-ray imaging plate to measure the c-axis orientation of HAp crystals in the specimens. Further, to measure the deformation behavior of HAp crystals, tensile tests were also conducted under X-ray irradiation and the deformation of interplanar spacing was measured. As a result, the c-axis of HAp crystals was aligned with the longitudinal direction of the trabecular specimens, even though the c-axis was aligned with the longitudinal direction of the diaphysis in the cortical bone of bovine femur. The elastic modulus and the deformation of HAp crystals in the trabecular specimens were smaller than those in the cortical bone of bovine femur.KeywordsBiomechanicsCancellous BoneTrabeculaElastic ModulusHydroxyapatite