Although head injury thresholds have been defined for adults, little is known quantitatively about the biomechanics of pediatric head injury. The objective of this dissertation was to quantify the age-dependent material properties of the human brain and skull and to determine their effect on the biomechanical response of the head to traumatic loading. Mechanical testing was performed on infant and adult porcine brain tissue and infant and adult porcine and infant human skull to define the age-related mechanical properties of these tissues. Brain tissue was tested in dynamic oscillatory simple shear from 20-200 Hz to determine its complex shear modulus. Skull tissue was tested in three-point bending and tension to failure at a quasi-static rate (2.54 mm/min) and a dynamic rate (2540 mm/min) to determine the age-dependent and loading rate-dependent properties of cranial bone and suture. Finite element models of the infant and adult brain and braincase were developed to investigate the age-dependent nature of intracranial strain distribution during impact loading.

The elastic and viscous components of the complex shear modulus of the brain changed significantly with the development of the cerebrum. These changes in material properties correlated with increases in brain mass, total cell number, and myelin, and a decrease in water content. The elastic modulus, ultimate stress, and energy absorbed to failure of cranial bone increased, and the ultimate strain decreased with age. Likewise, the elastic modulus, ultimate stress, and energy absorbed to failure increased with age for sutures. These factors predispose the head of the newborn to large, potentially injurious shape changes during traumatic loading as demonstrated in a parametric study of impact loading performed with the finite element models. In the finite element simulations of impact loading of the head, the intracranial strains within the infant brain were diffusely distributed throughout the brain while the intracranial strains within the brain of the adult model were focused under the impact site. These investigations are essential for predicting the unique mechanical response of the pediatric skull to traumatic loads associated with head injury and, thus, for defining head injury thresholds for children.