Search

Recently, brain injury has been mainly analyzed by computer simulation. However, simulation model of brain needed to obtain accurate analysis results has been shown variety of values. Simulation model reproduced deformational behavior of brain with velocity has not been built. We obtained relaxation curve from hemisphere indentation test for cerebral surface using our own experiment setup, and calculated shear modulus and viscosity. We built viscoelastic model of cerebral surface and evaluated effect of velocity, sites, and leptomeninx on mechanical properties. Our experiment showed that short term shear modulus with leptomeninx was approximately 1.4 times higher values than it without leptomeninx, and viscosity value in high speed range was lower than slow speed. We evinced that brain tissue depends on velocity on high speed range, and leptomeninx affects a rigidity of cerebral surface. Additionally, we confirmed that our viscoelastic model is numerically able to reproduce deformational behavior of brain on high speed range, and acquired parameter values for functions of viscoelastic model.

Twist drills are often used to prepare implant sites for the internal fixation of fractures, and the stability of the fixation, which depends directly on how securely the implants are held, depends on the quality of the bone around the pilot holes after implant site preparation. To optimize the design of surgical drills, this study evaluated the effects of the drill design elements (thinning, and the helix and point angles) on drilling characteristics (thrust force and temperature increase and duration) when drilling bone. We used mature porcine femurs because porcine bone resembles human bone, and measured the thrust force and bone temperature at three points during the drilling test using drills with different designs and a standard surgical drill. We found that types X, N, and R thinning were effective in reducing the thrust force, and a quick helix was effective in reducing temperature increase and duration when drilling cortical bone. However, no obvious relationship was observed between the drill design elements and the drilling characteristics, perhaps because the cutting system of a drill is complex. In the future, creating a more efficient evaluation method to overcome the complexity of the cutting system and examining the relationship between the drill design elements and the drilling characteristics should be carried out to improve the drilling performance of bone.

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.

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.

Adjacent segment degeneration (ASD) is an abnormal process that develops at spinal segments adjacent to the fused segment caused by biomechanical changes after spinal fusion. To avoid the adverse effects of spinal fusion on the adjacent segments, various flexible stabilization systems have been developed, of which the Graf system is one of the most widely used. We assessed the biomechanical influence of the Graf system and spinal fusion. The L3-L6 vertebrae were taken from porcine lumbar spines. A spinal motion tester displaced the end of the L3 vertebra to simulate continuous flexion/extension. Three cycles of flexion/extension were applied and the angular motion and intradiscal pressure were recorded during the third cycle for each test. The angular deformity at the flexible stabilized segment was suppressed until 4° of deformation; the deformity gradually increased after 4° and then finally equaled that of the intact spine. The maximum intradiscal pressure increased significantly in each segment fused and in the adjacent spinal segments using the Graf system. In conclusion, the Graf system reduces the motion of adjacent segments and may reduce the risk of ASD. Nevertheless, the relationship between ASD and the increase in the intradiscal pressure remains controversial.

We developed a new estimation system using rapid prototyping technology that focuses on the relationship between the architecture and mechanical properties of trabecular bone. The system uses three-dimensional acrylic resin models of trabecular bone constructed from micro-CT data to predict the mechanical properties of trabecular bone. We used this method to clarify the relationship between loading orientation and bone fragility in the vertebral trabecular bone of ovariectomized (OVX) rats. Twenty 6-week-old female Wistar rats were randomly divided into two groups (OVX and normal groups). Five rats from each group were killed at 3 and 6 weeks following operations and the L4 vertebra was removed. Bone specimens from both groups were scanned using a micro-CT system. Subsequently, resin models of the bone were fabricated at 60× magnification from the micro-CT data sets using laser stereolithography. The resin models were subjected to compressive testing in three orthogonal orientations corresponding to the craniocaudal, mediolateral, and anteroposterior anatomic axes. The results showed that the elastic modulus and ultimate stress were lower in the models of OVX rats than in the normal rats, the mechanical properties of trabecular bone structure from OVX rats deteriorated with increasing time postoperatively, and the elastic moduli in the mediolateral and anteroposterior axes were especially reduced relative to the decrease in the craniocaudal axis in the OVX rats.

Quantitative measurement of spinal rotational mobility is critical in assessing spinal instability. We have developed a system for intraoperative measurement of spinal mobility. The system consists of a motor-driven mechanical apparatus with a computerized controller, load cell, optical displacement transducer, and spinous process holders that allow handling of the spinal process without damaging the ligaments. In this study, we examined the ability of this measurement system to detect mobility and corresponding clinical instability of a destabilized model spine comprised of porcine lumbar segments. From the load-displacement curve, we determined three motion parameters: stiffness, neutral zone (NZ), and absorption energy (AE). To demonstrate the potential of the measurement system for clinical application, we applied five cycles of axial rotation to the segment ten times. The measurements were highly reproducible. To verify the utility of the measurement system, we tested destabilized functional spinal units in vitro. In this setting, stiffness and AE decreased and NZ increased with progressive destabilization of the model spine. Significant relationships were observed between the destabilized model and the biomechanical data.

The morbidity associated with idiopathic osteonecrosis of the femoral head (ION) is increasing. The primary goal of treatment for ION is to prevent collapse of the femoral head. With the exception of hip arthroplasties, current joint-preserving surgeries for ION require long-term reduction of the load placed on the hip joint. To allow these patients to return quickly to their daily and social activities, we have developed a novel extra-articular device that reduces the weight-bearing of the hip joint. In this study, we evaluated the load-bearing function and the range of motion of a hip joint equipped with the extra-articular device. To demonstrate load reduction on the hip joint with this device, we measured the contact pressure on the femoral head surface and the principal strain on the coxal bone during static loading conditions, which simulated the various phases of human gait. The range of motion of the hip joint with the device was measured using an electro-goniometer. The extra-articular device remarkably reduced the contact pressure on the hip joint, with some restriction in hip flexion. Our novel extra-articular device appears to be a promising tool to secure reductions in the weight-bearing function of the hip joint, and will be applicable to new bone regeneration therapies.

The purpose of this study was to clarify the dynamic changes in contact pressure distribution and three-dimensional ankle joint motion before and after lateral ligament injuries. Five fresh and frozen intact cadaveric ankles were examined. Each ankle was mounted on a specially designed frame that preserved five degrees of freedom motion. The direct linear transformation technique was used to measure the three-dimensional ankle motion, and a pressure-sensitive conductive rubber sensor was inserted into the talocrural joint space to determine the contact pressure distribution. The contact area on the talus for intact ankle moved anteriorly and laterally with increasing dorsiflexion. An area of high pressure was observed in the medial aspect of the articular surface after the ligament was cut. Supination significantly increased after a combined anterior talofibular ligament (ATF) and calcaneofibular ligament (CF) were cut in comparison with after only an ATF was cut, and no significant differences were observed in motional properties under each experimental condition.

For the technical improvement for brass instrument players it is important to obtain the detailed control parameters for embouchure building. While many investigators have reported the preliminary data on the muscle behavior, the precise aspects are unrevealed so far. The purpose of the present paper is to study dynamic perioral muscle behavior of French horn players and to investigate their lip valve function by measuring the contact pressure on teeth buccal surface during playing. It was shown from the experimental results that the advanced players contracted depressor angulioris and levator angulioris especially for high tone playing. It is considered that the combined contraction by these muscles contributes to forming smaller lip aperture being suitable to produce higher tones. Inversely a strong contraction of m. buccinator, which is widely believed to work to give hard tension to player's lip, was observed insignificantly in the advanced players.

Ultrasonic techniques were developed to study the characteristics for contact mechanics of an artificial hip joint. Total Hip Replacement model was used to determine contact pressure distribution on an artificial aceptabular cup subjected to compressive load ranged from 196 N to 588 N in four femur positions. The contact pressure was found to be non-uniform and reaches more than 6 MPa. It was shown that the tendency of the pressure distribution is in agreement with that obtained by the computer simulation. Some preliminary results were also presented to illustrate the effect of the direction and the magnitude of the load applied to a femoral head on the contact pressure distribution on the aceptabular cup and to evaluate the contact mechanism of the artificial hip joint.

In this work, a grip force dynamometer composed of pressure-sensitive conductive rubber was used to study the sensibility characteristics for grasping of a solid cylinder. The mechanical and physical parameters for ten normal male subjects (aged between 22 and 26) were measured at various cylinder diameters and weights. In addition, a direct linear transformation technique employing a video camera system was developed to determine the finger joint motion used to grasp the cylinder. The experimental results showed that the frictional coefficien of a palm is significantly dependent upon the deform ability of the soft tissue of the palm. It was found that the optimum cylinder diameter for easy grasping is nearly equal to the inner grip diameter formed by the fingers.

An ultrasonic technique was developed to study the characteristic for abrasion pattern of a rubber surface during stick slip motion and to demonstrate its applicability to the precisely contact pressure measurement utilizing Wigner distribution. Experiments were conducted using short cylindrical acril specimens pressed onto the rubber sheet bonded on a rotating disk. It was found that the contact pressure may be nearly zero soon after the locally high contact pressure area moves to the leading edge. In addition, the experimental results showed that the formation mechanism of the abrasion pattern observed on the rubber surface has close relation to locally sudden variation in the contact pressure due to a stick-slip phenomenon.

This paper is concerned with biomechanical analysis of the motion characteristics for grasping a solid cylinder. Contact pressure and surface electromyogram (surface EMG) of muscle flexor digitorum superficialis during grip motion were measured using a contact pressure measurement system with pressure-sensitive conductive rubber sensors and an electromyograph, respectively. In addition, direct linear transformation (DLT) technique with a video camera system is used to analyze three-dimensional joint motion of fingers. It was found that the tips of middle finger, ring finger and thumb are mainly used to stably grip the cylinder. The experimental results also showed that grip pressure increased with an increase in the weight of the cylinder with a constant diameter.

An acoustic emission technique was developed to study the tribological characteristic of boriding SKD steel using a pin-on-disk type wear testing machine with acoustic emission sensor. AE signal of 300 kHz frequency spectrum generated by crack propagation in the specimens was observed in the wear tesing. The R. M. S. value of the emission signal was expressed in terms of wear and friction parameters, The experimental results showed that AE generation from pin contact with a rotating disk indicates the feasibility of utilizing AE in boriding metal wear sensing.

An ultrasonic technique was developed to study the characteristic abrasion pattern on a rubber surface under stick slip motion and to demonstrate the precisely contact pressure measurement at the end of contact. Experiments were conducted using short cylindrical rubber specimens pressed onto the rotating acril disk. It was observed that the abrasion pattern was significantly dependent on the variation in contact pressure. In addition, the experimental results showed that the formation of abrasion pattern on the middle area of contact was stimulated by the stick slip motion.

A new type of shrink fitter, 'a hybrid shrink fitter', containing liquid such as a fusible alloy is proposed. The specimen materials are Al2O3 and Si3N4 for the shafts, SUS 304 for casings of the hybrid shrink fitters and SUS 403 for the metal rings. Fitting strengths were measured up to 600°C. The fitting strengths decreased with temperatures up to 200°C or 300°C and increased at higher temperatures. It was found that the hybrid shrink fitter had a higher apparent coefficient of thermal expansion than the monolithic shrink fitter. The effect of the number of slits on the fitting strength at elevated temperatures was also studied. The slit was essential for improving the fitting strength. The number of slits did not affect the fitting strength-temperature relationship if the number was 2 or more. The longevity of the hybrid shrink fitter was less than that of the monolithic shrink fitter at elevated temperatures.

This paper deals with the axisymmetric torsion problem of an infinite hollow cylinder with externally and internally circumferential cracks lying in different planes. Expressing the stress component along the crack plane as an appropriate series, the problem is reduced to the solution of an infinite system of simultaneous equations. Numerical results are presented in order to illustrate the effect of the distance between two crack planes on the stress distributions at the crack tips and stress intensity factors.

This paper is concerned with an asymmetric mixed boundary-value problem of an elastic half-space adhered by a rigid punch under shear stress. The behaviour of the adhesive layer is approximated by a combination of tension and shear springs. The normal and shear stresses on the adhesive region of the half-space are expressed by Jacobian polynomials. The problem is reduced to the solution of an infinite system of simultaneous equations. The distributions of stress and displacement on the surface of the half-space are illustrated for various values of the adhesion. The effects of the adhesion on the stress and displacement fields are also discussed.

In this paper, we present an elastic solution for the axisymmetric torsion problem of an infinite cylinder with circular and circumferential cracks lying on the same plane. Expressing the stress component along the crack plane as an appropriate series, we reduce the problem to the solution of an infinite system of simultaneous equations. Numerical results are shown in order to discuss the effect of the two crack depths on the displacement and stress distributions at the crack tips and stress intensity factors.