Effect of inter-species, gender, and breeding on the mechanical behavior of brain tissue.

Mechanical response of brain tissue deforming at high rates are needed to build high-fidelity computer models for traumatic brain injury (TBI) studies. Different types of mammalian brains have been used to obtain the constitutive behavior of tissue. It is necessary to examine how these different brains compare to each other in order to determine which animal might be the best surrogate for human brain tissue. In this experimental study, fresh brain tissue from three different mammals, two types of porcine breeds, and genders were loaded under uniaxial compression over a wide range of strain rates. The experiments at higher rates were conducted with a Kolsky bar modified for soft tissue characterization, whereas lower rate experiments were performed on a conventional hydraulic material test frame. Experimental results did not show any significant difference in high-rate compressive response of the brain tissue of different animals, different breeds, and different genders. However, there was significant rate dependence for all tissues tested, especially in the Kolsky bar range. Further investigation is necessary to identify the source of the rate effects.

Dynamic compressive response of bovine liver tissues.

This study aims to experimentally determine the strain rate effects on the compressive stress-strain behavior of bovine liver tissues. Fresh liver tissues were used to make specimens for mechanical loading. Experiments at quasi-static strain rates were conducted at 0.01 and 0.1 s(-1). Intermediate-rate experiments were performed at 1, 10, and 100 s(-1). High strain rate (1000, 2000, and 3000 s(-1)) experiments were conducted using a Kolsky bar modified for soft material characterization. A hollow transmission bar with semi-conductor strain gages was used to sense the weak forces from the soft specimens. Quartz-crystal force transducers were used to monitor valid testing conditions on the tissue specimens. The experiment results show that the compressive stress-strain response of the liver tissue is non-linear and highly rate-sensitive, especially when the strain rate is in the Kolsky bar range. The tissue stiffens significantly with increasing strain rate. The responses from liver tissues along and perpendicular to the liver surface were consistent, indicating isotropic behavior.

Dynamic mechanical response of bovine gray matter and white matter brain tissues under compression.

Dynamic responses of brain tissues are needed for predicting traumatic brain injury (TBI). We modified a dynamic experimental technique for characterizing high strain-rate mechanical behavior of brain tissues. Using the setup, the gray and white matters from bovine brains were characterized under compression to large strains at five different strain rates ranging from 0.01 to 3000/s. The white matter was examined both along and perpendicular to the coronal section for anisotropy characterization. The results show that both brain tissue matters are highly strain-rate sensitive. Differences between the white matter and gray matter in their mechanical responses are recorded. The white matter shows insignificant anisotropy over all strain rates. These results will lead to rate-dependent material modeling for dynamic event simulations.