This study proposes an alternative mechanical simulation protocol for ceramic femoral heads under in vivo-like conditions. A 3D pelvis model is obtained from CT images and the finite elements of the implanted models are validated based on Kwong's experimental results. The stress distribution of nine different femoral head models is then compared when using the conventional proof test (standard ISO 7206-10) and proposed test protocol (postoperative models). Both test methods show a decrease in the maximum stress when increasing the size of the femoral head and bore depth. However, for the stress distribution, the postoperative models reveal a concentration on the superior inner region of femoral head cranial, while the proof test shows an axisymmetric shape in the tangential direction. As a non-uniformed stress distribution increases the probability of fracture, the mechanical testing of ceramic femoral heads should be considered under in vivo-like conditions in order to improve the mechanical reliability of the joint. Thus, the current results show the necessity and viability of an alternative mechanical evaluation method for ceramic hip implants.
Manual wheelchair users have a high risk of injuries to the upper extremities due to the mechanical inefficiency of wheelchair propulsion motion. The kinetic analysis of the upper extremities during manual wheelchair propulsion in various conditions needed to be investigated. We developed and calibrated a wheelchair dynamometer for measuring kinetic parameters during wheelchair propulsion. We utilized the dynamometer to investigate and compare the propulsion torque and power of skilled and unskilled users under four different conditions. Skilled manual wheelchair users generated smaller torques with larger power than unskilled users and reacted alertly and sensitively to changing conditions. We expect that the results of this study may help to quantitatively evaluate the mechanical efficiency of manual wheelchair propulsion.
Potential complications after open wedge high tibial osteotomy (HTO) still remain unanswered as they are known to be primarily dependent on the surgical technique or the fixation strength. In this study, we evaluated the sensitivity of surgical variations (presence of bone graft, osteotomy line orientation and loading pattern) affecting post-operative stability using finite element analysis. Changes in stress distribution were also assessed at the lateral cortex bone and bone plate. A total six types of post-operative FE model were constructed to accommodate surgical variations based on the validated intact tibia model; Case 1 (lower level osteotomy, with no bone graft or with auto-tri-cortical bone), Case 2 (safe level osteotomy, with no bone graft or with auto-tri-cortical bone), Case 3 (upper level osteotomy, with no bone graft or with auto-tri-cortical bone). Two types of loading condition (axial compression_2450N with bending_240N and torsion_15Nm) were imparted. The use of bone graft material at the osteotomy site decreased the stress distribution at the lateral cortex bone and bone screw. And the lower level provided more post-operative stability than other osteotomy level (safe, upper). However, the ‘safe’ zone offered relatively similar results to those of the ‘lower’ zone. The osteotomy line near the lower end of the ‘safe’ zone was indeed the safest and most practical surgical approach as suggested in previous clinical studies. Therefore, our results suggested the use of bone graft with safe level osteotomy to assure the greatest post-operative stability and to reduce the likelihood of correction loss.
Aneurysm recanalization can be attributed to coil compaction and migration, which are affected by hemodynamic forces acting on the packed coil inside the aneurysm. The effects of coil bundle deformation on the hemodynamic changes in coil-inserted lateral aneurysm models were investigated using computational fluid dynamics methods incorporating fluid-structure interactions. Lateral aneurysms with normal and wide necks were modeled, and coil bundles were modeled as elastic spheres. The time-averaged mean velocity magnitude at the neck (MVN) and the time-averaged mean kinetic energy (MKE) were calculated to quantify the overall inflow strength and intra-aneurysmal flow activity, respectively. The MVNs and MKEs were higher in elastic coil models than in rigid models, and elastic coil models with lower Young's moduli had higher MVNs. Therefore, coil deformation caused by hemodynamic forces is suspected to provide an unfavorable hemodynamic environment for aneurysm embolization.
This study aimed to analyze the muscular activity associated with the proper function, stability, and mobility of the shoulder joint. In the field of orthopedics, the shoulder joint is recognized as having extensive mobility. Using an electromyograph (sEMG), the muscular activity in 10 elderly male subjects was analyzed during joint movements while performing isokinetic exercises. The muscular activity of an agonist was analyzed using both the percent maximum voluntary contraction (%MVC) and the EMG (µV) value before normalization. The %MVC quantified four motions (flexion, extension, abduction, and adduction) for the 10 upper limb muscles whereas the latter did not. The results showed that the pectoralis major (clavicular insertion) activated as an agonist during abduction and adduction. A comparison of when the muscles activated based on each motion revealed that the middle deltoid muscle activated the fastest during abduction. This research is expected to facilitate measurement of the shoulder function for both rehabilitation equipment and their associated programs.
Actin stress fibers (SFs) play a key role in regulation of cell adhesion, but the biochemical and biophysical properties intrinsic to SFs remain unclear. Here we extracted SFs from rat embryonic smooth muscle cells by deroofing, and evaluated the effects of varying ionic strength and temperature on their intactness. Wash buffers with ionic strength ranging from 90 to 490 mM were prepared, and the extracted SFs were incubated in a buffer with a particular ionic strength for 10 min or 24 h. Light and electron microscopy revealed that the extracted SFs comprised tightly packed straight bundles at low ionic strengths that became looser and exhibited a ragged pattern at high ionic strengths. The expression of α-actinin associated with the extracted SFs decreased with the increase in ionic strength. Unexpectedly, non-muscle myosin II and smooth muscle myosin in the extracted SFs displayed comparable expression levels over the different ionic strengths. ATP-induced contractility was better preserved at low ionic strengths, including the physiological ionic strength of 170 mM. The rate of ATP-induced enzymatic activity increased with increase in temperature, but the difference was not statistically significant. These results demonstrate that low ionic strength produces extracted SFs that are more intact with regard to structure and function.
Motion perception is estimated from integrated multi-sensory cues including visual, somatosensory, and vestibular organ's signal. The sensory integration is affected by various factors such as sensory condition, environment and one's consciousness on these factors. There are relatively less number of studies that focus on the effect of consciousness to the sensory integration. In this study, we examined the effect of awareness of sensory conflict to linear motion perception. Ten subjects reported their perceived direction of motion with coherent or reversed vision condition. To examine the consciousness effect, subjects participated with and without being aware of sensory conflict condition. When subjects were not informed that there could be sensory conflict, vision played a dominant role in their motion perception. On the other hand, when subjects were aware of possible fault in visual cues, relative reliance on visual cue compared to the other sensory cues was significantly reduced, especially under sensory conflict condition. This result implies that the relative weight of sensory information for estimating motion perception might be regulated by the consciousness factor.
Diffuse axonal injury (DAI), a major component of traumatic brain injury, is associated with rapid deformation of brain tissue resulting in the stretching of neural axons. Focal axonal swelling, which is the morphological hallmarks of DAI pathology, leads to the disconnection of neurons from tissues, resulting in cell death. Our goal is better understanding of neuronal tolerance and help to predicting the pathogenesis of DAI from mechanical loading to the head. In present study, we developed an in vitro stretch injury device that subjected cultured cells to a wide range of mechanical stretch that are experienced during in vivo head injury. Then using this device, PC12 cells, which extend structurally axon-like cylindrical protrusions in culture, were stretched to a strain of 0.15, 0.30, or 1.00 at strain rates of 30, 40, or 80 s-1, or left as static culture. Following mechanical loading, we assessed neurite swelling resulting in neuronal detachment from culture substrate and neuronal death. As a result, the increase in early neurite swelling was dependent on the severity of the stretch, and neuronal adhesion and viability at 24 h post-injury decrease in a stretch-dependent manner. These results suggest that the formation of neurite swellings correlates with the progression to neuronal death.
In this study, a new Braille display is constructed based on the vibration of a Shape Memory Alloy (SMA) wire. To present Braille information, a vibration actuator is used instead of conventional Braille dots. According to the temperature-dependent characteristic shrinkage and the vest ration to the initial length of an SMA wire, a vibration actuator which can be driven by several [Hz]-100 [Hz] pulse signals has been developed. A method for presenting Braille information is proposed by the application of the developed actuator to a Braille display. In this research, multiple actuators constructed by using metal pins (0.7 [mm] in diameter, 3 [mm] in length) and SMA wires (50 [um] in diameter, 3 [mm] in length), are placed as to form standard Braille. The actuators are vibrated by PWM signals with different frequencies and appropriate timings, and the effectiveness of the proposed method for Braille display is verified by experiments. From the experimental results, the highest recognition rate of 100 [%] was achieved under the conditions of 50 [Hz] vibration frequency and 500 [ms] time delay. This means the vibration patterns effectively stimulated the Meissner corpuscles, and helped the subjects properly discriminate Braille characters presented by the developed display. Good evaluations were received from the subjects who are visually-impaired.
Snoring was once regarded as an indication of good sleep, but recently it has been known to be one of the symptoms which indicate sleep disordered breathing such as sleep apnea syndrome. Especially, loud snoring caused by oral breathing during sleep is often found in many apnea/hypopnea patients. Thus, it is important to detect oral snoring for medical treatment in the earlier stage, but we cannot know our own snoring. This paper describes a method to detect oral snoring by extracting the acoustic properties of snoring sounds. According to the FFT amplitude spectra, nasal snoring sounds consist of only lower frequency components less than 500Hz, whereas oral snoring sounds consist of unique intensity peaks at 1kHz and lower frequency components less than 500Hz as well. According to the bibliographical point of view, such lower frequency components indicate the palatal snoring, and the intensity peak at around 1kHz indicates the tongue base snoring. Therefore, it is obvious that nasal snoring sounds can be regarded as simple palatal snoring whereas oral snoring sounds are a mixture of palatal and tongue base snoring sounds. So, we focused on the fundamental frequency and maximum of the amplitude spectrum in a specific band. In this paper, the Harmonic Product Spectrum (HPS) method is used for estimating the fundamental frequency and the k-Nearest Neighbor method is adopted for classifying oral/nasal snoring sounds. As a result, over 89% of snoring sounds are successfully classified under the four kinds of cross validation evaluations.
Skull fractures occurring under various impacts are required to be evaluated during forensic investigations or during design of a head protection device. Finite element analysis using a human head model is an effective evaluation tool for it, because investigating of the behavior of skull fracture such as the start and the progress can be easily performed. JARI Head Tolerance Curve (JHTC), which is an existing criterion for skull fracture based on the cadaver head drop tests, uses head acceleration as the parameter, though the fractures are mainly caused by stress concentration on local area. In this study, we tried to develop stress-based criteria for skull fracture, and to simulate skull fracture by using a head finite element model, which we previously developed. Forehead dropping simulations with five different conditions were performed, and the results were found to be nearly equivalent to the JHTC tests in terms of effective acceleration of head and its duration time. We then determined critical stresses for skull fracture as a function of duration time, based on the time histories of stresses on the skull surface in the five simulation results. Furthermore, we applied our criteria to two forehead impact simulations. We could observe fracture on the skull followed by sharply decreasing in stress on fractured elements as well as increasing in stress on its neighboring elements, and also variation in shapes and ranges of fractured element distribution. These results indicate that the criteria could evaluate skull fracture in detail under different patterns of impact.
Magnetic resonance elastography (MRE) is a nondestructive method for measuring the hardness and softness of living tissue by means of magnetic resonance imaging (MRI) coupled with mechanical excitation of the subject. The shear modulus of a tissue is related to the velocity of transverse waves propagating through it, and local movements are obtained from MRI phase images. Micro MRI systems are available for high-resolution MRE measurements of soft materials. Longitudinal waves are effective for long-distance wave propagation from small excitation areas in micro MRI systems, and the transverse waves produced by the longitudinal waves can be used for elastography. This study proposes an excitation system comprising a high-power vibration generator and bar-shaped vibration transmitter made from an elastic material. The transmission characteristics of the glass-fiber-reinforced plastic bar-shaped transducer were evaluated by measuring the accelerations at its base and tip. The performance of the excitation system, which focused on the effects of frequency and amplitude, was investigated for measuring storage and loss modulus distributions in agarose gel. This system could transfer longitudinal waves with an amplitude of 0.5 mm and frequency between 50 and 250 Hz, without significant damping. Moreover, the excitation capabilities for gel phantoms were evaluated by MRE using 0.3T micro MRI equipment. A large amplitude of 0.5 mm and high frequency of 250 Hz produced less data scatter than smaller amplitudes and lower frequencies. MRE performance improved upon using strong excitations.