26:T42d,

The effects of strain rate and low-gamma irradiation on the compressive properties of ultra-high molecular-weight polyethylene (UHMWPE) were investigated. Gamma irradiation was performed at 30 kGy in nitrogen or at 29 kGy in air without post-irradiation treatment. Quasi-static and impact compressive tests using the split-Hopkinson pressure-bar technique were performed to measure stress–strain relations up to a true strain of 8% at strain rates of between 0.0004 and 260 s⁻¹. For both unirradiated and gamma-irradiated UHMWPE specimens, an increase in the strain rate significantly increased the Young's modulus and the 0.5% yield stress. Gamma irradiation in air significantly increased the Young's modulus, as determined by quasi-static and impact compressive testing, and the 0.5% yield stress, as determined by impact compressive testing. The strain-rate dependence in the power-law relationship was similar to that observed for strain rates ranging from 0.02 to 0.10 s⁻¹ (Kurtz et al., Biomaterials 23, 2002, pp. 3681–3697).

27:T4fb,

The objective of this study was to test the hypothesis that there is one model for the interface between the passive layer on the surface of an orthopaedic alloy and an electrolyte that has clinical relevance. To this end, electrochemical impedance spectroscopy measurements were made on mechanically-polished test specimens fabricated from three orthopaedic alloys [two Ti-based ones (Ti–6Al–4V and Ti–13Nb–13Zr) and a very-low-nickel austenitic stainless steel, Biodur^® 108] while they were immersed in phosphate buffered saline (PBS) solution, at 37±1°C, over a period of 25 d. Through a statistical comparison between the experimental results (Nyquist and Bode plots) and those computed using seven different equivalent electrical circuits (each representing a different model of the aforementioned interface), it was found that one circuit (comprising an arrangement of three resistances and three capacitances in series with a resistor representing the solution resistance) provided the best-fit in all three alloy surface-PBS solution systems, thus providing support for the working hypothesis. The variation of each of the circuit elements with time of immersion of the specimen in the PBS solution and the study limitation are discussed.

28:T4d6,

There are few studies on the effect of in situ fibroblast viability on the mechanical properties of skin. This study examines the effect of poison (2-deoxy-D-glucose) and strain on fibroblast viability and stress-relaxation in skin samples from the backs of 20 same-age male rats. Skin samples were either soaked in Kreb's solution or in poison and was then either strained or left unstrained, for a total of four different treatment groups. All samples were fixed and processed for apoptosis assay and light microscopy. The viability study showed that strained tissues soaked in Kreb's solution had significantly more apoptotic cells compared to unstrained tissues soaked in the same solution. For tissues soaked and strained in poison the increase in apoptotic cells was negligible. Samples strained in Kreb's solution were found to have greater stress relaxation compared to samples strained in Kreb's solution with poison. The amount of stress relaxation was found to correlate with the number of viable fibroblasts in the tissues; tissues with more viable fibroblasts have lower stress relaxation. According to the relationships observed, fibroblasts do play an important role in the mechanical properties of rat skin tissues.

29:T498,

To obtain an appropriate model for the simulation of the biomechanical behavior of brain tissue and the deformation of ventricles, in particular, we have developed a novel computerized plain strain finite element model. For optimum results, a multiple loading solutions approach using various tissue parameters for the simulation of epidural hematoma have been tested. For this purpose, CT-Scan of a patient with traumatic epidural hematoma has been modeled. By changing the tiss