In this paper a complex prosthesis of dental implants, inserted in a mandible bone, has been analyzed using a virtual model. The study has been performed by means of a three-dimensional finite element model including the implants, the bridging structure and the bone. The interaction between implant screws and bone has been simulated in detail. Four different load conditions has been implemented to mimic the masticatory phase. The stress distribution in the implants and in the bone has been evaluated. Effects of possible temperature variation and assembling errors have been also taken into account. Moreover, the stiffening effect of the stabilizing bar that connect the implants has been also discussed. Starting from the results of the numerical investigations an optimization of the shape of the implants has been proposed in order to optimize the assembling procedure.
A gait analysis was performed to estimate chaotic behavior of the human body motion. The purpose of this study is to apply the chaos analysis technique to joint motions of both upper and lower extremities and to compare their characteristics between men and women. A novel approach is to extend the nonlinear chaos analysis to eleven major joints including the neck and both the upper and the lower extremities. The maximal Lyapunov exponent (MLE) was calculated from the time series of the flexion-extension angle of each joint. Differences in MLE values showed no statistical significance between the right and the left sides, nor between men and women for every joint. For overall joints, however, the MLE values were found to be statistically different between the two genders (p<0.05). The correlation analysis between two different joints also showed statistical difference between the two genders. These results will address differences in the chaotic characteristics of the joint movements between men and women during the treadmill walking.
In this study, a non destructive monitoring system for osteoblastic calcification in tissue-engineered bone in vitro was proposed and developed utilizing near-infrared light. The system consists of LEDs and a photo detector (PD) underneath a culture dish. The LED irradiates near-infrared light (I0) at 850 nm increasing its intensity to a tissue-engineered bone placed in the culture dish. The diffuse reflectance light (I) from the engineered bone is detected by the PD and the degree of calcification is evaluated by the slope of I0-I curve. A steeper slope represents higher degree of calcification. This system was calibrated with type I collagen sponge scaffolds deposited artificially with hydroxyapatite and the degree of calcification was expressed in bulk density (mg/cm3). Using this system, osteoblastic calcification in tissue-engineered bones composed of the collagen sponge scaffold and rat-primary cultured osteoblasts or MC3T3-E1 cells was monitored for 42 days. The system succeeded not only in monitoring an increase in the bulk density of the engineered bones with the culture period, but also in distinguishing the difference of calcification ability between the cells, i.e., the higher ability of rat-primary cells and the lower ability of MC3T3-E1 cells, which could not be confirmed by the observation under visible light. The results suggested the efficacy of our system using near infrared light in long-term monitoring of oeteogenesis in vitro, by which this optical monitoring system could contribute to bone tissue engineering and to basic bone biology as well.
The kinetics analysis of ankle, knee and hip joints during gait is fundamental for rehabilitation and clinical diagnosis but data are commonly obtained by means of the laboratory-restricted equipment such as a force plate and optical camera system, which usually require complicated computing programs and professional operation. In this study, we have developed a wearable sensor system to facilitate joint kinetics analysis to assess body movement in daily activities. The sensor system is composed of a shoe-based force sensor which measures ground reaction force (GRF) and center of pressure (CoP), and a leg-attached motion sensor consisting of three uniaxial gyroscopes units which detect lower limbs movement. This paper presents a kinetics analysis of ankle, knee and hip joints in the sagittal plane by using the sensor system on human normal level walking during whole gait phases. In order to estimate the joint kinetics, an inverse kinetics method based on the sensing signals and gait characteristics was developed. In the validation experiments with 10 subjects, joint kinetics was calculated using data synchronously measured by the sensor system and a force plate & optical camera system. The root mean square (RMS) differences of the ankle, knee and hip joints moments between the two systems in a gait cycle were (2±0.34) (mean±standard deviation) Nm, (7.2±1.34) Nm and (11.2±1.3) Nm, being (5.4±0.7)%, (6±0.32)% and (6.1±0.25)% of the maximal magnitude of ankle, knee and hip joints moments respectively. The RMS differences of the ankle, knee and hip joints powers between the two systems in a gait cycle were (4.2±0.4) W, (5.7±2.1) W and (5.7±0.3) W, being (8.4±0.4)%, (4.1±0.5)% and (6.4±0.4)% of the maximal magnitude of joint powers respectively. The experimental results demonstrate the feasibility and effectiveness of the joint kinetics analysis using the wearable sensor system for a daily application in gait analysis.
In this study the tribological characteristics of a sliding pair of Al2O3 nanocomposites against Al2O3 were investigated. Al2O3 nanocomposites are proposed as a candidate material for the fabrication of prostheses. Nanopowders of Al2O3 (AKP 50, 300 nm), Y-TZP; tetragonal zirconia polycrystal stabilized with 8mol % of yttria (TZ-8YS, 100 nm) and TiO2 (PS-25, 50 nm) were mixed and hot pressed. A ball-on-plate tribometer was used for the wear test. The nanocomposite plate specimen was rubbed against the Al2O3 ball at a frequency of 1 Hz for 1 h, with a load of 49 N. Distilled water and fetal bovine serum solution (FBSS) were used as lubricants. Mechanical properties were estimated using the indentation method. It was found that the specific wear rate of Al2O3 nanocomposites was about 2-6x10-8 mm3/Nm and the coefficient of friction from 0.3 to 0.5 for FBSS. The nanocomposites containing 15mol% Y-TZP (ATZ150) had the lowest wear rate (1.77x10-8 mm3/Nm) for FBSS. Worn surfaces were observed using SEM. Furthermore, AFM and XPS were used to study the effect of the serum lubricant on the articulating surface of the Al2O3 nanocomposites, and AlPO4 was found on the wear track of the samples tested in FBSS.
The reason why the wrinkle suddenly becomes prominent at a middle age is addressed from biomechanical standpoint. The multistage buckling theory we have derived concludes that the sudden enlargement of wrinkle comes from a switch of the specific buckling mode from the horny buckling to the epidermal buckling. In this study, the validity of this conclusion was reexamined by the finite element buckling analysis of the human facial skin with a linear aging model. Comparison of results between the beam model and the finite element model unraveled the mechanism of the buckling mode switch. By simulating the three cases: epidermal aging, dermal aging, and full aging, we found that the mode switch mainly comes from the epidermal aging, that is, the stiffening and thinning of the epidermis. The dermal aging was not a trigger of the mode switch in the linear buckling of linear aging skin model.
A method is proposed for the rapid measurement of translational diffusion coefficient by employing the unique multiphase flow of perfectly miscible incompressible fluids in microchannels. The molecule of interest is injected, as a bolus or continuously, into the middle phase of a three phase flow system. Subsequently, the phase or stream is depleted of molecule by diffusion into the adjacent streams through the common interface. By monitoring the elution profile of the molecule, one may obtain estimates of the diffusion coefficient under fixed experimental conditions. Transport of molecule in the microchannel is described by a transient convection-diffusion-dispersion model. Analytical and numerical solutions are provided to illustrate the change of elution profile with stream velocity and other design parameters. The diffusion coefficient is estimated from a graphical plot. It is shown that diffusion coefficient may be measured without prior knowledge of dispersion. Experimental data is presented for the proteins, fibrinogen and insulin. A number of advantages over the T-sensor and Taylor-Aris methods are highlighted.
The juvenile form of hallux valgus (JHV) develops during the growth period of children and adolescents. The purpose of our study was to investigate the kinematic changes of the lower extremity segments during gait in subjects with and without JHV. Subjects diagnosed with JHV (n = 27, age = 20.5 ± 1.2 yrs, mass = 61.2 ± 10.1 kg) were compared to a healthy controls (n = 11, age = 21.5 ± 1.3 yrs, mass = 66.6 ± 12.5 kg). Spatial parameters along with 3-D video motion kinematic data were collected from the pelvis, hip, knee, and ankle of both lower extremities as the subjects walked at self-selected speeds. Results were analyzed with a two-factor ANOVA followed by Fisher LSD post hoc test. Maximum hip extension was smaller in the JHV groups (p<0.05) compared to the control group and maximal flexion at the hip that was greater in the JHV groups than in the control group (p<0.01). The one-sided JHV group walked with a shorter stance due to lack of full hip extension, contributing to a smaller knee extension range (p<0.01) at the late stance. In the JHV group the larger step coupled with increased plantar-flexion (p<0.01) may result from the greater hip flexion found during the loading response. These data suggest the influence of the JHV deformation on the kinematic parameters of the lower extremities during gait.
This paper investigated buckling phenomena of the spine induced by the growth of vertebral bodies that have potential to cause idiopathic scoliosis. In the previous study, we presented a hypothesis that idiopathic scoliosis is a buckling phenomena induced by the growth of vertebral bodies based on the similarity of the clinical single and double-major curves with the results of the fourth and sixth buckling modes, respectively, as analyzed by the finite-elements method using linear buckling theory. However, this theory is valid for infinitesimal deformation and is not applicable to estimation of stability for post-buckling behavior. In this study, we developed a program to analyze deformation histories caused by the growth of vertebral bodies considering the geometrical nonlinearity and investigated buckling phenomena. We assumed that growth represents generation of non-elastic bulk strain. To exclude modes correctable by posture change, we considered constraints at the cervical spine. Using the developed program, we analyzed deformation histories induced by the growth of vertebral bodies and obtained deformation histories including buckling phenomena with side-bending modes similar to clinical curves. However, the magnitudes of deformations were in the sub-millimeter order that is too small for the etiology of idiopathic scoliosis by itself. Based on the results, we suggested that participation of other phenomena, such as bone remodeling caused by the stresses at the side-bending deformations, will be necessary.
The cystic duct is a very complicated conduit that connects the gallbladder to the common bile duct. The geometry of the cystic duct and its functions, in particular the valves of Heister, in the flow of bile into and out of the gallbladder have always been a subject of speculation. It has been suggested variously that their function is to: impede the flow of bile into the gallbladder, prevent the outflow of bile from the gallbladder, or prevent the collapse of cystic duct. Presented in this paper are the results of a novel experiment to assess the role of the valves of Heister during both the filling and the emptying phases of the gallbladder. The results suggest that the existence of these valves helps both the filling and the emptying of the gallbladder by providing structural support and preventing the duct from total collapse. A surge of pressure upstream of the cystic duct is observed prior to the opening of the cystic duct which is consistent with previous in-vivo biological observations.
For stability analysis of the lumbar spine, a hypothesis is presented that the disc has stress sensors driving a feedback mechanism which can react to the imposed loads by adjusting the contraction of muscles. A three dimensional model of the musculoskeletal system with a detailed lumbar spine finite element model was combined with an optimization technique to calculate muscle forces. The musculoskeletal model consisted of a detailed whole lumbar spine, pelvis, and simplified trunk model. For computational efficiency, the vertebral body and pelvis were modeled as a rigid body and rigid truss elements were used for the rib cage construction. Minimization for deviation of nucleus pressure or Tresca stress in the nucleus was chosen for muscle force calculations. The results indicate that the originally C-shaped lumbar spine was flattened at the upper level, while the more lordotic curvature was generated at the lower level. Muscle forces generated not only in deep muscles, but also in extensor muscles, play an important role in sustaining the lumbar spine to the external load. The resultant forces acting in each vertebra show somewhat different magnitudes and directions compared to the follower load that mimics the deep muscle contraction in in-vitro experiments.
We have performed numerical simulations to examine saccular cerebral aneurysm formation at the outer curve of a bent artery. A U-shaped arterial geometry with torsion, which was modeled on part of the human internal carotid artery, has been employed. A new numerical model was proposed to take into account proliferation as well as degradation of the arterial wall. Proliferation of the arterial wall was modeled by surface area expansion in high wall shear stress region. Based on wall shear stress distribution on the artery, we have investigated aneurysm formation for the following three conditions: (a) strength degradation of the wall, (b) proliferation of the wall, and (c) both strength degradation and proliferation of the wall. A saccular aneurysm shape was not observed when considering only arterial wall degradation up to 90%. However, the saccular shape formed when proliferation of the arterial wall was also taken into consideration. The resultant shape was consistent with clinical observations. Our findings have suggested that a saccular aneurysm may not be formed by degradation of the arterial wall alone, but also require its proliferation.
Computer based three-dimensional (3D) reconstruction technique is widely used in clinical practices and its accuracy is still improving due to introducing of high resolution imaging modalities. Practically, two-dimensional X-ray image might be considered as one of major tools in orthopaedics, due to its lower cost and lower dose of radiation than computer tomography (CT). The purpose of the current study is generating 3D model of femoral bone using conventional X-ray images incorporating the anatomical parameters into a referential 3D model. For the 3D reconstruction, the 2D shape and specific parameters of bone were firstly measured from X-ray images. Then, the referential CT model was modified as follows: the axial scaling, shearing transformation and radial scaling. In this study, the 3D reconstruction algorithm was tested using femoral X-ray images from the 28 years old male. The current study showed that the 3D reconstruction technique by using X-ray images can be useful and feasible in clinical practices. It could easily generate 3D femoral model not only with saving time and costs, but also less radiation exposure to the patients.