A knee joint injury is one of the most common injuries in car-pedestrian accidents. For the examination of the knee joint injury tolerance and the determination of the absolute range of knee joint injury criteria, we performed dynamic three-point bending tests on the porcine knee joint using the own drop impact test setup. During the test, an impactor (mass: 21 kg) was launched toward the lateral side of the specimen placed on a three-point bending support. The femoral epiphysis was completely fractured when the drop height was 700 mm. Multiple damages to the medial collateral ligament and other soft tissues such as the posterior cruciate ligament were observed when the drop height was 500 mm. Only the medial collateral ligament was damaged when the drop height was 300 mm. No injury was observed when the drop height was 100 mm. The calculation of the maximum bending moment acting at the knee joint showed that the injury criterion range was from 136 to 320 Nm. This range includes the values of injury criterion in previous studies on the human knee joint. Thus, there is hardly any difference between the injury criteria for the porcine and human knee joints.

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Reductions in growth population and increased longevity have increased the demand for healthcare worker. In the near future, humanlike robot will be designed to assist and eventually replace the need for human in certain work areas. Our interest is to design a robot that has human characteristic and cooperate with human in moving an object. To design such robot, first, we need to understand how a human manages to cooperate naturally and smoothly with another human. The human characteristic that we are interested in is how human communicate using implicit and explicit information exchange. This includes audiovisual and touch senses that enable both humans to achieve good interaction to complete a cooperative task in moving an object. In order to understand the effects of communication between two humans, we devised an experimental object to be moved cooperatively by two humans. In this cooperative task, one human worked as a leader to initiate, determine the trajectory and final position of the object while the other human acted as a follower and followed the leader's path. The experiment object was put into position along with the force sensors and the data collected was analyzed by computers. Based on the data analyzed, we compared the actual velocity of the experiment subjects and the ideal minimum jerk velocity profile. This enables us to study the effects of force, motion, starting signal and target information in order to determine the cooperative task ideal condition. From our research, we have found the ideal condition of the human characteristic for human-human cooperative task and therefore this paper is proposing a way of thinking to design robot which can be used for human robot cooperative task.

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In this study, the effects of a dynamic strain in the cytotoxicity and mortality of the PC12 cell line were evaluated by using impact experiment with huge acceleration. In order to consider the influence of axonal damage on nerve cells, 2 types of nerve cells were used for the impact experiments, i.e. with and without axons. The cytotoxicity and mortality of cells were evaluated by the input acceleration, strain and strain rate and the strain rate seemed to be the most appropriate to evaluate the cytotoxicity and mortality of cells. Cells with axons showed higher cytotoxicity and mortality than cells without axons, when the strain rate was larger than 13.11 (1/s). Damage to axons was confirmed by terminal swellings and beadings of the axons. These data indicated that the presence of axons increased the cytotoxicity and mortality of cells.

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Fixation plates and screws are commonly used to promote stability and stiffness to fractures through the compression of bone fragments. However, the difference between the rigidity of an implant and the bone causes stress shielding, and can lead to excessive resorption in the vicinity of implants, thereby causing subsequent implant loosening and failure of fixation. In this study, finite element analysis (FEA) software is employed to generate a simplified three-dimensional model of a transverse femoral fracture affixed with a plate. The first model discussed in this paper is a validation study, proving the qualitative accuracy of using FEA, while the second model is one of increased fidelity and is used in a parametric study to delve into the effects of plate and screw parameters on the level of resultant stress shielding in bone underlying the plate. The models discussed reveal insight into the nature of applied fixation plates. Direct compression plating, although inherently stable, will cause stress shielding in bone and can result in bone loss, screw avulsion, and fixation failure. However, as seen in the parametric study, which is in agreement with previous works, a decrease in implant flexural rigidity, through a decrease in plate thickness and angle, will decrease the level of stress shielding present in a bone-implant system. As well, the importance of screw placement, implant materials, and the future use of FEA as a prospective tool is discussed.

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The aim of this study was to investigate the static and dynamic properties of the flexion withdrawal reflex modulated by hip changes in human spinal cord injury. The influence of the hip position and passive movement were tested in six subjects with chronic spinal cord injury. Each subject was placed in a supine position and lower limb was fixed with the knee at 23.7±16.0 degrees flexion and the ankle at 33.3±5.2 degrees plantar flexion. A train of 10 stimulus pulses were applied at 200Hz to the skin of the medial arch to elicit the nociceptive flexion reflexes. From results of the regression analysis, activation of flexor muscles (tibialis anterior and illiopsoas) during static hip angle changes has a linear relationship with respect to hip angle (P<0.05). As the hip flexion angle increases, the EMG activity decreases. A significant linear relationship was also found between the reflex activity of flexor muscle (illiopsoas) and hip angular velocity during both hip flexion and hip extension movement (P<0.05). In order to validate the reflex response, we compared the static and dynamic gains of estimated activation with measured electromyogram of tibialis anterior. From this study, we postulate that flexor muscle activities of nociceptive flexion reflex have linear relationship with hip angle and angular velocity.

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The possibility of pressure-induced leaching of vitamin E from inside of vitamin E-blended ultrahigh molecular weight polyethylene (UHMWPE) was investigated. UHMWPE specimens were pressed against a base plate, and leached vitamin E was dissolved in ethanol. The quantification of vitamin E in ethanol was carried out by fluorescence spectrophotometry. Vitamin E was confirmed to leach from inside of the vitamin E-blended UHMWPE specimens under compressive load, and the amount of leached vitamin E was positively correlated with the applied load.

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Halocynthia roretzi, a solitary ascidian, can swell and deflate its solid, leather-like tunic largely, but it is not clear whether the tunic deforms actively. Cellulose Iβ, which is predominant in higher plants, is also present in the tunic as a highly crystalline form. The elastic modulus of its whisker crystalline is considerably high. Substantial amounts of chitin sulfate-like, water-soluble polysaccharide were also present. These polysaccharides alone would barely cause tunic deformation. If the tunic's flexible deformation is self-controlled, it would have another element in addition to the polysaccharide, and it would be an ideal model for designing a novel material. The hypothesis of this study was that the H. roretzi tunic has a nervous system, myocytes, and elastic fibers controlling its flexible deformation. Using acetylcholine and touch as stimuli, the tunic samples were found to deform at acetylcholine concentrations ≥20 µM, indicating the existence of a nervous system, and to have mechanosensitivity. The Bodian, Klüver-Barrera, acetylcholinesterase, immunohistochemical (α-smooth muscle actin), and Elastica-Masson staining methods indicated the presence of a nervous system, myocytes, a region rich in α-smooth muscle actin, and elastic fibers, validating the hypothesis. The self-controlled system in the tunic is useful to understand the properties of the tunic and to design a novel actively deforming material.

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Background. Ultrasound measurement of osteoarthritis cartilage thickness is not sufficiently accurate if constant sound velocity is used. The aim of this study was to investigate the applicability of estimating the sound velocity using echo reflectance from the cartilage surface. Methods. Change in measurement error of cartilage thickness was evaluated using collagenase-treated osteochondral plugs. Sound velocity was calculated from the reflectance ratio, and the reference thickness was measured using a needle method. Findings. The relative errors of thickness measurements using constant sound velocity were increased after collagenase treatment. The errors using calculated sound velocity showed no significant difference between intact and degenerated samples. Interpretation. The collagenase treatment-induced error was reduced from 7% to 2% in absolute value, suggesting the applicability of the correction method for ultrasound measurement.

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