Topographical mapping of the mechanical characteristics of the human neurocranium considering the role of individual layers.

The site-dependent load-deformation behavior of the human neurocranium and the load dissipation within the three-layered composite is not well understood. This study mechanically investigated 257 human frontal, temporal, parietal and occipital neurocranial bone samples at an age range of 2 to 94 years, using three-point bending tests. Samples were tested as full-thickness three-layered composites, as well as separated with both diploë attached and removed. Right temporal samples were the thinnest samples of all tested regions (median < 5 mm; p < 0.001) and withstood lowest failure loads (median < 762 N; p < 0.001). Outer tables were thicker and showed higher failure loads (median 2.4 mm; median 264 N) than inner tables (median 1.7 mm, p < 0.001; median 132 N, p = 0.003). The presence of diploë attached to outer and inner tables led to a significant reduction in bending strength (with diploë: median < 60 MPa; without diploë: median > 90 MPa, p < 0.001). Composites (r = 0.243, p = 0.011) and inner tables with attached diploë (r = 0.214, p = 0.032) revealed positive correlations between sample thickness and age. The three-layered composite is four times more load-resistant compared to the outer table and eight times more compared to the inner table.