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Abstract: Postmortem preservation conditions may be one of factors contributing to wide material property variations in brain tissues in literature. The objective of present study was to determine the effects of preservation temperatures on high strain-rate material properties of brain tissues using the split Hopkinson pressure bar (SHPB). Porcine brains were harvested immediately after sacrifice, sliced into 2mm thickness, preserved in ice cold (group A, 10 samples) and 37°C (group B, 9 samples) saline solution and warmed to 37°C just prior to the test. A SHPB with tube aluminum transmission bar and semi-conductor strain gauges were used to enhance transmitted wave signals. Data were gathered using a digital acquisition system and processed to obtain stress–strain curves. All tests were conducted within 4h postmortem. The mean strain-rate was 2487±72s−1. A repeated measures model with specimen-level random effects was used to analyze log transformed stress–strain responses through the entire loading range. The mean stress–strain curves with ±95% confidence bands demonstrated typical power relationships with the power value of 2.4519 (standard error, 0.0436) for group A and 2.2657 (standard error, 0.0443) for group B, indicating that responses for the two groups are significantly different. Stresses and tangent moduli rose with increasing strain levels in both groups. These findings indicate that storage temperatures affected brain tissue material properties and preserving tissues at 37°C produced a stiffer response at high strain-rates. Therefore, it is necessary to incorporate material properties obtained from appropriately preserved tissues to accurately predict the responses of brain using stress analyses models, such as finite element simulations. [ABSTRACT FROM AUTHOR]

Abstract: The objective of this study was to test the hypothesis that the human lumbosacral joint behaves differently from L1–L5 joints and provides primary moment–rotation responses under pure moment flexion and extension and left and right lateral bending on a level-by-level basis. In addition, range of motion (ROM) and stiffness data were extracted from the moment–rotation responses. Ten T12–S1 column specimens with ages ranging from 27 to 68 years (mean: 50.6±13.2) were tested at a load level of 4.0Nm. Nonlinear flexion and extension and left and right lateral bending moment–rotation responses at each spinal level are reported in the form of a logarithmic function. The mean ROM was the greatest at the L5–S1 level under flexion (7.37±3.69°) and extension (4.62±2.56°) and at the L3–L4 level under lateral bending (4.04±1.11°). The mean ROM was the least at the L1–L2 level under flexion (2.42±0.90°), L2–L3 level under extension (1.58±0.63°), and L1–L2 level under lateral bending (2.50±0.75°). The present study proved the hypothesis that L5–S1 motions are significantly greater than L1–L5 motions under flexion and extension loadings, but the hypothesis was found to be untrue under the lateral bending mode. These experimental data are useful in the improved validation of FE models, which will increase the confidence of stress analysis and other modeling applications. [Copyright &y& Elsevier]