Keywords

Paper information

Jiro Sakamoto, “Preface”, Journal of Biomechanical Science and Engineering, Vol. 5, No. 5 (2010), pp.484-484 . doi:10.1299/jbse.5.484

Pneumothorax is characterized by lung collapse. Its effect on hemodynamics, especially on pulmonary arterial blood flow, remains unclear. This patient-specific study investigated the effects of lung deformation on pulmonary blood flow during acute phase and after recovery. Arterial geometry was extracted up to the fifth generation from computed tomography images in three patients and reconstructed. Different geometrical parameters (artery bores, area ratios, and between-branch angles) were computed. The shapes of the pulmonary trunk and its branches were affected strongly by pneumothorax. To clarify the effect of geometrical perturbations on blood flow, the Navier--Stokes equations for a steady laminar flow of Newtonian incompressible fluid were solved in a reconstructed domain. The change in flow structure between acute phase and recovery was associated with variations in flow rate ratio between the right and left lungs. This study shows, possibly for the first time, that from a patient-specific numerical test, pneumothorax has a considerable impact on pulmonary arterial morphology and hemodynamics.

Keywords

Pneumothorax, Computational Fluid Dynamics, Morphological Analysis, Pulmonary Arteries, Patient-specific Model

Paper information

Jean-Joseph CHRISTOPHE, Takuji ISHIKAWA, Noriaki MATSUKI, Yohsuke IMAI, Kei TAKASE, Marc THIRIET and Takami YAMAGUCHI, “Patient-specific Morphological and Blood Flow Analysis of Pulmonary Artery in the Case of Severe Deformations of the Lung due to Pneumothorax”, Journal of Biomechanical Science and Engineering, Vol. 5, No. 5 (2010), pp.485-498 . doi:10.1299/jbse.5.485

Patient-specific nonlinear finite element analysis (FEA) is promising for evaluating the recovery of vertebral strength. Vertebral strength is closely related to inner vertebral stress distribution and is used to assess the fracture risk for individual osteoporotic patients during drug treatment. Moreover, stress distribution is affected by individual bone shape, bone density distribution and nonlinear behavior of the mechanical properties of bone. To investigate the effectiveness of FEA considering these factors for the evaluation of drug treatment effects, patient-specific nonlinear FEAs of the first lumbar vertebrae in patients undergoing a 3-year drug treatment were performed. Changes in fracture load and distribution of failure elements in the FE models at four time points (before therapy, and after 6 and 12 months and 3 years of therapy) were compared with those of average bone density. The FEAs demonstrated that failure elements decreased notably, and fracture load increased gradually by the 3-year time point, suggesting that the vertebrae were strengthened as a result of drug treatments. Furthermore, statistical tests indicated that mechanical evaluation using the nonlinear FEAs is more sensitive for evaluating drug effects on osteoporotic bone than assessments based on average bone density.

Keywords

Computational Biomechanics, Bone Strength, Patient-Specific Image-Based Modeling, Vertebra, Osteoporosis, Therapeutic Effect

Paper information

Daisuke TAWARA, Jiro SAKAMOTO, Hideki MURAKAMI, Norio KAWAHARA, Juhachi ODA and Katsuro TOMITA, “Mechanical Therapeutic Effects in Osteoporotic L1-Vertebrae Evaluated by Nonlinear Patient-specific Finite Element Analysis”, Journal of Biomechanical Science and Engineering, Vol. 5, No. 5 (2010), pp.499-514 . doi:10.1299/jbse.5.499

Tensile tests of a single cell were simulated in order to understand the effects of the initial orientation of actin fibers (AFs) on global tensile properties. The properties examined included cell deformation, stiffness, and AF behavior. In the model used, the mechanical properties of cellular components, including the cell membrane with an associated actin network, nuclear envelope, and AFs, are expressed as a result of springs that generate force as a function of their extension. Cell shape during the tensile test was determined by a quasi-static approach couched in the framework of the minimum energy concept. Cells with various initial AF orientations were prepared; in particular, AFs in four different initial orientations, namely random (mean ± SD of the initial orientation angle, 46.4 ± 26.9°), parallel to the stretched direction (3.8 ± 3.5°), perpendicular (85.9 ± 2.6°), and diagonally oriented (44.5 ± 3.6°) were examined. The results show a significant drop in initial stiffness with an increase in mean initial AF orientation angles of 0 to 45°. The initial stiffness of the cell with parallel-oriented AFs was much larger than that with perpendicularly oriented AFs. The results also demonstrate that cell elongation induces a passive reorientation of AFs in a stretched direction, thereby causing an increase in cell stiffness. When comparing the rate of change for cell stiffness of the diagonally oriented model with that of the randomly oriented model, our data reveal that the rate of change of cell stiffness is characterized not only by the mean of the initial AF orientation angle, but also by the variation of their distribution.

Keywords

Cell, Mechanical Properties, Spring Network Model, Actin Filaments, Simulation

Paper information

Yoshihiro UJIHARA, Masanori NAKAMURA, Hiroshi MIYAZAKI and Shigeo WADA, “Effects of the Initial Orientation of Actin Fibers on Global Tensile Properties of Cells”, Journal of Biomechanical Science and Engineering, Vol. 5, No. 5 (2010), pp.515-525 . doi:10.1299/jbse.5.515

Three-dimensional maxillary bone models of a male and a female patient were constructed using their CT-images. The distributions of Young's modulus were estimated from their bone mineral density distributions. Total six implants were embedded into each of the maxillary models. Finite element analysis of the maxilla models was then performed in order to assess the concentrations of strain energy density especially in the vicinities of the embedded implants. It was found that in both models, strain energy density was concentrated especially around the right-molar implant, suggesting outbreak of damage and subsequent absorption of bone tissue in this region. The female model with smaller size and lower bone density exhibited much higher localized concentration of strain energy density than the male model. Therefore, a modified placement of the right-molar implant was then introduced into the female model and such high concentration was effectively reduced by using the inclined and longer implant. It is thus concluded that this kind of three-dimensional modeling can clinically be used to predict the optimal implant treatment for each of dental patients.

Keywords

Dental Biomechanics, CT-Image Based Modeling, Finite Element Analysis, Maxillary Bone Model, Bone Quality

Paper information

Takaaki ARAHIRA, Mitsugu TODO, Yasuyuki MATSUSHITA and Kiyoshi KOYANO, “Biomechanical Analysis of Implant Treatment for Fully Edentulous Maxillas”, Journal of Biomechanical Science and Engineering, Vol. 5, No. 5 (2010), pp.526-538 . doi:10.1299/jbse.5.526

Bone structure is renewed or restructured in part by a load-dependent remodeling. In this study, a mathematical model of bone surface remodeling over a wide range of strain was established. We assumed that in a low strain range, bone resorption occurs at an accelerated rate with strain decrease owing to low strain-induced osteocyte apoptosis, and that in a high strain range, bone formation occurs at an accelerated rate with strain increase (targeted remodeling). In a physiological strain range, bone formation or resorption was assumed to occur stochastically according to the degree of local stress non-uniformity. The utility of the present model was examined through three-dimensional numerical simulation of femoral trabecular architecture.

Keywords

Computational Biomechanics, Remodeling Turnover, Osteocyte Apoptosis, Targeted Remodeling

Paper information

Jiyean KWON, Hisashi NAITO, Takeshi MATSUMOTO and Masao TANAKA, “Simulation Model of Trabecular Bone Remodeling Considering Effects of Osteocyte Apoptosis and Targeted Remodeling”, Journal of Biomechanical Science and Engineering, Vol. 5, No. 5 (2010), pp.539-551 . doi:10.1299/jbse.5.539

Trabecular bone structure is determined by a balance between osteoblastic bone formation and osteoclastic bone resorption, which is regulated partly by osteocytes according to their mechanical environments. There have been a number of studies on bone remodeling in response to mechanical stimuli, mainly in the physiological range. This study uses a mathematical model previously formulated for surface remodeling available even for disuse and overuse ranges considering osteocyte apoptosis and targeted remodeling. Thus, the present model allows exhibiting the changes of trabecular bone structure under, below, and beyond the daily loading condition. In this study, we carried out computer simulation of bone remodeling in human femur under normal daily loading condition and reduced weight-bearing conditions (infrequent and cane-assisted walking conditions). Decreased trabecular bone with reducing loading condition was shown, and the trabecular bone structure at various degrees of disuse was consistent to Singh Index for osteoporosis diagnosis.

Keywords

Biomechanics, Bone Remodeling, Disuse, Trabecular Structure, Osteoporotic Femur

Paper information

Jiyean KWON, Hisashi NAITO, Takeshi MATSUMOTO and Masao TANAKA, “Computational Study on Trabecular Bone Remodeling in Human Femur under Reduced Weight-bearing Conditions”, Journal of Biomechanical Science and Engineering, Vol. 5, No. 5 (2010), pp.552-564 . doi:10.1299/jbse.5.552

The nasal cavity performs several important functions for the inhaled air, such as temperature and humidity adjustments. Although it is necessary to obtain velocity, temperature, and humidity distributions during inhalation in order to understand the nasal cavity's functions, it is difficult to measure them noninvasively in the nasal cavity. Therefore, we have continued to study nasal flow simulation with heat and humidity transport. In such a simulation, the governing equations include a continuum equation and the equations describing momentum, energy, and water transport. The temperature and humidity of the inhaled air are adjusted by heat and water exchange on the nasal cavity wall's surface. Therefore, in the simulation, these roles of the wall in the energy and water transport equations were included as the boundary conditions. Although in related studies of nasal flow simulation with heat and humidity transport, the nasal cavity wall's surface temperature and humidity were constant, here they were treated as degrees of using Newton's cooling law. A flow including temperature and humidity in a realistic human nasal cavity shape was simulated. The simulation results agreed well with the measurements reported by Keck at al. Therefore, this study concludes that our model can simulate the heat and humidity exchange occurring in the nasal cavity. In addition, it was found that the temperature and humidity adjustment functions worked effectively in the front and narrow regions of the nasal cavity.

Keywords

Nasal Flow, Computational Fluid Dynamics, Realistic Shape, Heat and Humidity

Paper information

Kiyoshi KUMAHATA, Futoshi MORI, Shigeru ISHIKAWA and Teruo MATSUZAWA, “Nasal Flow Simulation Using Heat and Humidity Models”, Journal of Biomechanical Science and Engineering, Vol. 5, No. 5 (2010), pp.565-577 . doi:10.1299/jbse.5.565

Blood is a concentrated suspension of blood cells in plasma. Motion and deformation of red blood cells (RBCs) and their mechanical interaction play important roles in determining blood rheology. Here, we propose a computational model of mesoscopic blood flow where the particulate and continuum natures of blood coexist. We modeled blood flow at two different scales, RBC flow at the microscopic level and continuum at the macroscopic level. A hematocrit-dependent viscosity was considered to take account of the effects of the spatial variation of RBC concentrations on the macroscopic flow. Starting with a Poiseuille flow, the blood flow in a cylindrical channel was simulated. Due to fluid shears, RBCs migrated radially toward the center of flow channel, causing a higher fluid viscosity around the central axis than that near the wall of the channel. Such a spatial variation in viscosity altered the velocity profile of macroscopic blood flow and further changed the RBC distribution within the channel. An iterative calculation resulted in a decrease in flow velocity at the center of the flow channel, as observed in vivo and in vitro. These results address the potential of the present computational approach in the analysis of mesoscopic blood flow.

Keywords

Mesoscopic Simulation, Blood Flow, Red Blood Cell, Rheology, Hematocrit

Paper information

Masanori NAKAMURA and Shigeo WADA, “Mesoscopic Blood Flow Simulation Considering Hematocrit-Dependent Viscosity”, Journal of Biomechanical Science and Engineering, Vol. 5, No. 5 (2010), pp.578-590 . doi:10.1299/jbse.5.578