In this study, effects of strain rate on the mechanical properties of injection-molded poly(L-lactide) (PLLA) were investigated experimentally. The effect of crystallinity on the strain rate dependency of mechanical properties of PLLA was also examined by annealing the specimens at 70 and 130 °C for 24 hours. In order to characterize the mechanical properties, tensile and compressive tests were conducted. The results of tensile tests indicate that the Young's modulus kept constant up to strain rate of 10^-1. On the other hand, tensile strength of non-annealing, 70°C-24h and 130°C-24 specimens increased with increasing strain rates up to 10^-1, 10^-2 and 10^-3, respectively, and decreased or kept constant because of decrease in the fracture strain with increasing strain rate. The effect of strain rate became lower with increasing crystallinity, which means the strain rate dependency of the PLLA under tensile loading is more effective in the amorphous region. The results of compressive tests indicate that the compressive Young's modulus kept constant up to strain rate of 10^-1. On the other hand, 0.2 % proof stress increased with increasing strain rate. This tendency was similar to the tensile test.

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Aging of population is a problem that is perceived globally. An increase in the elderly population causes a corresponding increase in the number of traffic accidents and injured pedestrians. In general, the most common injured body region of a pedestrian involved in a traffic accident is the lower extremity. In order to reduce the severity of pedestrian injuries, we need to experimentally predict the risk of bone fracture using biological specimens. In this study, we constructed an experimental setup for impact measurement. We utilized a torsion spring as the energy source and used porcine hind legs to replicate the human lower extremity while performing side impact tests. Strain gages were used to directly measure the dynamic responses of the cortical bone. From the results of the measurement of the strain distributions in the femoral diaphysis, we observed that higher strain occurred in the region nearer to the proximal. The maximum value of the strains in the lateral side of the femur was less than that in the medial side. Using the strain values, we quantitatively predicted the risk of femoral fracture in each region. Hence, our method, which is used for directly measuring the dynamic responses of the cortical bone, can be effectively used in biological tests to elucidate the nature of the injuries sustained by an accident victim.

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Thorax plays a crucial role in shielding internal organs from external loads. To establish a rational safety criterion for traffic accidents, it is important that we understand the mechanical behaviors of the thorax. We studied the response of thorax to impact experimentally. The purpose of this study is to understand the characterization of thoracic structure from measurement parameters by impact test. The specimen used was porcine thorax, the size of which was approximately equal to human thorax, after removing the internal organs. Using original test apparatus, the specimen was subjected to low energy impact and a sensitivity study was conducted to explore various parameters, including the response to the impact load, strain on each rib, and the acceleration and displacement in the thorax. Comparison of impact locations (front, back, and lateral) showed characteristic variations among the results. A frontal impact produced large acceleration and displacement. Therefore, it could be expected to stress the internal organs directly. In the case of an impact from behind, the impact response load was higher and the deformation of thorax was remarkably small. It appeared that the thoracic resists backward impact, and provides protection of internal organs. In lateral impact, the concentrated load tends to occur in the ribs, and the rib strain was high. Hence, the rib parts were prone to fracture, and the internal organs were subject to increased risk of secondary damages of the bone fracture due to bone sticking organs. In conjunction with the impact tests, static compressive tests were conducted. The deformation behavior of the thorax is grossly affected by the constraints of the binding of ligaments connecting bones. Therefore, this structure provides smooth elasticity by transforming the whole structure when a load is applied to the thoracic parts. This provided confirmation of the structural characteristics that were obvious in impact testing. This is the first time that attention has been paid to the thoracic structure and its deformation behavior has been investigated. The response of thoracic structures to external loads requires further research.

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The present paper describes a method for 3-dimensional (3D) automated preoperative planning of the femoral component (stem) in total hip arthroplasty (THA). Stem planning is formulated as a problem to determine the optimal parameters of position, rotation, and stem size, based on 3D surface models of host bone reconstructed from CT images, which includes the femur and femoral canal. An objective function that represents the fitness between the femoral canal and stem surfaces is defined. We also defined positional and rotational constraints derived from previous studies on femoral anatomy. Maximization is performed by the Powell method using initial values equally sampled within the possible solution space. We obtained parameters that maximize the objective function by exhaustive adjustment of the parameters. We applied the proposed method to 17 cases, and the proposed method was experimentally evaluated according to differences between planning results of the automated system and those of an experienced surgeon. Preoperative planning was also performed by a surgeon to evaluate performance of the automated system. The difference in stem size was less than 1 size in all cases, and the surgeon agreed with the planning results of the proposed method in 14 cases. In those 14 cases, mean errors of position and orientation were 3.2 mm and 4.6 deg., respectively. The proposed method thus appears applicable in preoperative planning of the stem.

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Static and cyclic compression tests of bovine cortical bone were carried out. For both tests, compressive stress was applied along longitudinal axis of bones and fracture surfaces were parallel to the loading direction. Damage accumulation during tests was monitored by the measurements of acoustic emission (AE) signals and ultrasonic wave velocity. For the static compression test, specimens fractured catastrophically and the most of AE signals were detected close to final fracture, i.e. few damage accumulation was detected. On the other hand, AE events increased and wave velocity decreased gradually during fatigue fracture of bone. A majority of AE signals were detected during unloading and they formed characteristic ‘AE bands’. AE wavelet analysis demonstrated that the peak frequencies of unloading AE, as well as loading AE, were equivalent to the resonant frequency of the specimen thickness. Finally, it was strongly suggested that microcrack extension due to wedging effect of debris took place during unloading in the fatigue process of cortical bone under cyclic compression.

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The mechanism of cerebral contusion was studied by using finite element analysis. Prior to numerical analysis of a finite element human head model, experimental study of an impact loading for a water-filled acrylic cylindrical container was carried out. The frequency of fluctuation of internal pressure was close to the natural frequency of the acrylic container. The human head model was analyzed by finite element analysis and the numerical result was compared with the result of the experimental study reported by Nahum and good agreement was obtained. In impact analysis, mass and velocity of the impactor were changed so as to keep the energy constant and intracranial pressure fluctuations of the impact side and the opposite side were obtained. When the input force duration was short, the thumping pressure fluctuation between the positive and negative pressure with higher frequencies were observed both at the impact side and the opposite side. As the input force duration became longer, the pressure fluctuation was suppressed and the positive pressure became dominant at the impact side and the negative pressure became dominant at the opposite side, and lower frequencies became dominant.

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Kinesins, biomolecular motors moving along microtubules (MTs) in cells, can potentially be utilized as nano-scale transport systems with an inverted gliding assay, in which the MTs glide on a kinesin-coated surface. Although the key requirements include controls of gliding direction and velocity of MTs, the details of motility properties of MTs have not been well known. In this study, we quantitatively measured angular and gliding velocities, particularly focusing on the effects of MT length and kinesin density. The gliding assay of MTs of up to 20 μm in length was performed on a substrate coated with the kinesin density of 7.5, 38, and 75 μg/ml that resulted in the kinesin spacing of 7.8, 4.2, and 3.1 μm, respectively. The angular velocity for MTs shorter than kinesin spacings significantly decreased with increasing their length, and that for MTs longer than kinesin spacings was not affected by their length. Moreover, the angular velocity was substantially higher at lower kinesin density. These results suggest that both the number of associated kinesins with MTs and the kinesin spacings may contribute to the gliding direction. In contrast, the gliding velocity was independent of the MT length, ranging from 0.3 to 0.5 μm/s with decreasing the kinesin density. This may potentially imply the existence of an underlying mechanism with respect to the number of kinesins per the unit length of MTs. Towards development of high throughput nano-scale transport systems, long MTs and low kinesin densities would be effective for high directionality and high velocity, respectively.

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