Morphology and Mechanics of the Young Minipig Cranium

The Göttingen miniature pig is a useful surrogate to understand mechanisms of traumatic brain injury (TBI) in the human. However, the mechanical response of the minipig skull has not been previously reported. In this study, cranial samples were extracted from the skulls of adolescent minipigs (six months of age, average weight of 13.8 kg). The microstructure was first characterized using high-resolution μCT. A highly gradient structure was observed, with the bone volume fraction (BVF) almost doubling in the through-thickness (depth) dimension. These specimens were then mechanically loaded in quasi-static compression. The surface strain distribution along the loading direction was measured during the experiments using digital image correlation (DIC). Depth-dependent moduli were derived from the measured DIC strains rather than machine displacement, due to the large gradient in morphology. An elasticity-morphology relationship from literature was extended to represent the modulus variation in the functionally gradient skull structure (BVF), by calibrating the relationship with the experimentally derived local moduli. The model enables the prediction of local moduli based solely on the morphological parameter BVF measured with μCT, and also provided an estimation of the modulus of the bony phase of the cranium.