Effect of Flexible Back on Energy Absorption during Landing in Cats： A Biomechanical Investigation

Cats are characterized by their excellent landing ability. During the landing, they extend and bend their flexible backs. This study was undertaken to examine the effect of flexible back on impact attenuation. We collected kinematic and ground reaction force data from cats performing self-initiated jump down at different heights. Based on these measurements, the mechanical energy and elastic back energy were calculated. Further, we derived a beam model to predict back stiffness from the morphology of the vertebral spines. We found that cat could actively modulate the bending level of flexible back and the landing angle at different heights, making some kinetic energy be stored briefly as elastic strain energy in the back. This mechanism allows cat to reduce the kinetic energy dissipated by limbs and improve the efficiency of energy absorption. These results can provide bio- logical inspiration for the design of a flexible spine on a landing robot, and we anticipated their use in the energy absorption equipments for planetary exploration.     

Biomechanical properties of sterilized human auditory ossicles.

Bone allograft material is treated with sterilization methods to prevent the transmission of diseases from the donor to the recipient. The effect of some of these treatments on the integrity of the bone is unknown. This study was performed to evaluate the effect of several sterilization methods on the mechanical behaviour of human middle ear bones. Due to the size and composition of the bones (approximately 1.5 mm diameter by 4 mm long), mechanical testing options were limited to the traditional platens compression test. Experiments were first performed with synthetic bone to evaluate the precision of this test applied to small specimens. Following this, fresh frozen human ossicles were thawed and sterilized with (i) 1 N NaOH (n = 12); (ii) 0.9% LpH, a phenolic solution (n = 12); or (iii) steam at 134 degrees C (n = 18). A group of 26 control specimens did not receive any sterilization treatment. Material and structural properties were determined from axial compression testing. Results from the synthetic bone showed that the test was reproducible, with standard deviations less than 20% of the means. Significant differences occurred in stiffness and ultimate force values between NaOH-treated and autoclaved bones when compared to normals (p<0.05), but not for LpH-treated bones. LpH is not approved for medical use, so NaOH is the most appropriate of the treatments studied for the sterilization of ossicle allografts.