Biomechanical testing

A servohydraulic materials testing machine (MTS 858 Mini Bionix II; MTS Systems Corp., Minneapolis, MN, USA) was used to subject the femurs and vertebrae to three-point bending and axial compression. Prior to the testing, a preload with 0.5 N as the contact force was applied on the surface of the mid-shaft of femur at a speed range of 0.1–0.2 mm/min from the first stage to later stages. The lumbar vertebrae (L4) of rats were subjected to compression to failure at a displacement rate of 6 mm/min. TestStar II software was used to generate and analyze the load-deformation curves. Force and displacement data were measured and recorded following the fracture of the specimen. The load-deformation curve identified the following biomechanical parameters: maximum stress (MPa; the maximum load per cross-sectional area), maximum load (N; the load at the maximum failure point), Young’s modulus (GPa; maximum slope of the stress-strain curve). and stiffness (N/mm; the slope of the linear region).