Biomechanical differences between inner and outer layers of the parietal cortical bone

The cranial vault protects the brain from physical injuries, with a dome‐shaped three‐layered structure, composed of inner and outer tables of cortical bone and the diploe sandwiched in between. The composite of the vault wall suggests independent biomechanical purposes for every stratum. However, how the relationship between the external and internal cortex and how their material properties are correlated to maximize its capabilities to undertake functional loadings and minimize the employment of bone mass have not been systematically studied. It is hypothesized that bone mass and elastic properties are different between two cortical layers. In this study, twelve pairs of the cortical samples from the parietal bone of a female baboon were collected, with each inner‐outer cortical paired sample from the same site. Cortical thicknesses and densities were measured, and elastic properties were assessed using ultrasonic technique. Results demonstrated remarkable difference in both thickness (F= 20.434, p 蠄0.05) and density (F=6.830, p= 0.016) between paired samples of inner and outer cortex. Differences in orthotropic elastic behavior were found for both E 1 (F= 17.506, p 蠄0.05) and E 3 (F= 33.737, p 蠄0.05)between the two cortical layers as well. How these differences are linked to the stress environments of the inner and outer cranial cortical layers awaits further studies. Supported by NSF BCS‐0725183, and COLCIENCIAS (Bogotá, Colombia).