Skeletal muscles develop forces as a result of muscle activation for human locomotion. To know the force generating ability of skeletal muscles is important to understand the muscle functions. Computer simulation is a useful tool for estimating the force generating ability. Therefore we have developed a three-dimensional (3D) finite element software to simulate both the so-called passive behavior of biological soft tissues and the muscle active behavior. The software is based on a nonlinear finite element setting for almost incompressible hyperelastic materials, where a total Lagrangian formulation, a mixed type displacement-pressure finite element and a fully implicit time integration scheme are adopted. The active stress as a result of muscle contraction is modeled by Hill-type model. Here, we investigated the effect of tendon stiffness within the range indicated in several literatures on the generated force at the Achilles tendon during isometric contraction of the triceps surae muscle. 3D FE-model of a human triceps surae muscle reconstructed by magnetic resonance images, which have the 3D distribution of the fascicle arrangement within the muscles. The stiffer tendon generated higher force at the Achilles tendon than the low-stiffness tendon, and the largest generated force was 1.45 times greater than the smallest one. It is, therefore, important to carefully obtain the material parameters from in vivo experimental observations. In this software, the subject-specific geometry and material properties can be used in the simulation. This software may therefore become a valuable tool for studying on orthopedics and rehabilitation planning, as well as for improving our understanding of muscle mechanics.
Although boundary element (BE) based methods are highly accurate for simulating capsule suspensions in Stokes flows, computational time has been a major issue, even when only a few capsules are simulated. We propose a full graphics processing unit (GPU) implementation of a numerical method coupling the BE method of fluid mechanics with the finite element method of membrane mechanics. In single GPU computing, the performance achieves 0.12 TFlop/s when computing one capsule (2562 nodes and 5120 elements) and 0.29 TFlop/s for two capsules. The performance increases with the number of capsules, achieving a maximum of 0.59 TFlop/s. We also implement a multi-GPU method with the data communication overlapping the computation. A weak scaling test shows perfect scalability for any number of computational nodes per GPU, indicating that the communication time is completely hidden. For a practical use of the present results, we estimate the computational time required for 10000 time steps. When we simulate one capsule and two capsules on one GPU, only 2.0 and 9.1 minutes are required to complete the simulation, respectively, and a simulation with 256 capsules on 16 GPUs takes 3.8 days.
Diffuse axonal injury (DAI), a major component of traumatic brain injury, is associated with rapid deformation of brain tissue resulting in the stretching of neuronal axons. Focal axonal beading, which is the morphological hallmark of DAI pathology, leads to the disconnection of neurons from tissues and results in cell death. Our goal is to achieve a better understanding of neuronal tolerance and help predict the pathogenesis of DAI from mechanical loading to the head. In the present study, we developed an experimental model that subjected cultured neurons to uniaxial stretch by controlling the direction of axonal elongation with a microfluidic culture technique and examined the effect of strains along the axon on cell damage. Neurites from PC 12 cells that differentiate into neurons with structurally axon-like cylindrical protrusions by nerve growth factor were extended at 0°, 45°, and 90° relative to the tensile direction by using a fabricated polydimethylsiloxane (PDMS) piece with microgrooves in combination with a PDMS substrate. The morphology of the same neurites was observed before and after stretching with a strain of 0.22 at a strain rate of 27 s-1. As a result, swellings along neurites oriented at 0° increased immediately following stretching and were sustained for 24 h. In contrast, swellings along neurites oriented at 45° and 90° transiently increased within 1 h following stretching. Although more ruptures were observed in neurites oriented at 0° and 90° than in those oriented at 45°, the number of neurites and cells did not differ among orientation conditions. These results suggest that the difference in strain along the axon induces axonal injuries differing in type and degree. They also suggest that the strain on the axon, rather than that on the cell-cultured substrate, is important for evaluating neuronal damage.
Human can realize flexible and skillful movements by controlling his/her musculoskeletal system and the interactive force with environments appropriately. However it still exist many uncertain biological motor characteristics in human movements even for a simple task. This paper aims to analyze and evaluate acceleration characteristics of the human hand during quick arm motion. First, the dynamic manipulability of end-point via muscle forces, called Human Muscular Mobility Ellipsoid (HMME), is newly defined. Next, the direction-dependent acceleration characteristic of the human hand motion is examined and analyzed its geometrical properties with an approximation ellipses of measured data. It is also discussed the problem that the conventional measures relative to the performance of end-point acceleration cannot represent the geometrical properties of human generated hand acceleration in good agreement with the measured data. Finally, the merits of HMME compared with the conventional measures is then demonstrated with a set of experimental results and computed results: HMME can be utilized in representing the geometric properties of human hand acceleration.
Dental plaque, which adheres to the surfaces of dental implants and remains in the gingival crevices, can cause peri-implantitis, which is similar to periodontal disease; consequently, cleaning the dental plaque from these surfaces is very important. In recent times, in order to improve their biocompatibility, the surfaces of these implants have been roughened. This has made it very difficult to remove the dental plaque from pits introduced into the surface to roughen it using oral toothbrushes. As the impacts caused by a cavitating jet can clean metallic surfaces, the jet can remove the plaque from these implants. As expected, dental plaque varies depending on each individual's oral conditions, so the distribution in the cleaning efficiency is scattered. In this paper, we propose a method for evaluating the efficiency of cleaning dental plaque on titanium. Dental plaque was allowed to accumulate on titanium plates placed on stents in the mouths of volunteers for three days. After removing the plates from the stents, they were exposed to a cavitating jet. The area cleaned on each plate was measured by dyeing. In order to investigate the effect of the surface roughness of the plate, a mirror finished plate and a roughened plate were used. It was concluded that the cavitating jet can clean dental plaque and that the residual dental plaque RDP (%) can be expressed by RDP = 100e–at where t is the exposure time to the jet and a is a constant representing the cleaning efficiency.
Exercise is effective as a preventive modality of osteoporosis because bone formation is accelerated by mechanical loading. However, elderly patients with osteoporosis are often difficult to exercise, which brings some risks of fractures during exercise with a fall. We focused on electrically-elicited muscle contraction to mechanically stimulate bone formation without any voluntary physical activities. The osteogenic effect of this method has been reported previously, however, it is unknown yet what the stimulation regimen is desirable to maximize the osteogenic effect. To provide basic knowledge to determine effective stimulation patterns in this method, this study aimed to investigate the effect of stimulation frequency on the osteogenic capability of electrical muscle stimulation in rats. The left quadriceps of rats were stimulated electrically for 30 min per day for 3 consecutive days under anesthesia. The stimulation waveform was a series of pulse trains composed of pulses with amplitude of 2 mA, 552 μs duration, and 50% duty ratio. The cyclic muscle contractions were generated by reversing the polarity of the electrical stimulation at 2, 10, 20, 40, or 80Hz. The stimulation effects were evaluated at the levels of gene expression and bone formation using RT-PCR and bone histomorphometry, respectively. Muscle stimulation at 20 Hz elicited a significantly higher expression level of osteocalcin mRNAs than those at the other frequencies. The 20-Hz stimulation also yielded the highest bone formation rate. However, these results did not correspond to the results of mechanical stimulation factors, including total number of contractions and average and cumulative muscle contraction forces during the stimulation period, suggesting a mechanism other than a dose-dependent effect of mechanical stimulation on osteogenesis. It was concluded that 20 Hz was the most effective frequency for eliciting the osteogenic effect of electric muscle stimulation in the rat. This finding provides useful information for establishing a stimulation regimen in clinical application of this method.
We simulated the flow behavior of a single red blood cell (RBC) passing through a two-dimensional stenosed microvessel. Blood flow was computed using the lattice Boltzmann method, and the fluid-membrane interaction between the flow field and deformable RBC was incorporated using the immersed boundary method. The vessel diameter and length are 20 and 50 μm, respectively. Two semicircular stenoses were arranged on the upper and lower walls. We investigated the influence of upstream RBC position of vessel width direction and inclination angle against the main flow on RBC deformation and flow resistance when the RBC flowed through the stenosis. The simulation results indicated two flow patterns depending on the upstream position and inclination angle. When the upstream position was near the vessel wall, the average flow resistance increased due to RBC migration to the vessel center. By contrast, when the upstream position was near the vessel center and the inclination angle against the main flow was 90°, the flow resistance increased due to the large RBC deformation. These results can assist in understanding the processes of circulatory diseases with stenosis.
The objective of this study was to examine the applicability of the musculoskeletal model to the sit-to-stand (STS) motion, especially focusing on the time-varying muscle load of the Erector Spinae. The musculoskeletal model was previously developed in order to estimate the effect of mechanical unbalance induced by pregnancy, which was mainly due to the increase in weight of the uterus. An experiment was carried out in order to validate the musculoskeletal model. In the experiment, non-pregnant subjects wearing an artificial pregnancy jacket performed the STS motion at three speeds. The experimental and simulated results of the muscle load of the Erector Spinae were then compared. From the comparison for the time histories of the muscle load, it was found that the characteristic tendencies observed in the experimental data were also observed in the simulated data. This suggests sufficient capabilities of the developed musculoskeletal model to predict the time-varying muscle load during the STS motion. The average muscle load of the Erector Spinae during the STS motion in the artificially-pregnant condition became 11% higher than that in the non-pregnant condition both for the experiment and simulation. This consistency between the experiment and simulation suggests the sufficient quantitative capability of the developed musculoskeletal model to predict the muscle load. Through the validated musculoskeletal model, the muscle load of the Erector Spinae during the STS motion for the non-pregnant and pregnant conditions were compared. From the comparison between the non-pregnant, artificially-pregnant and pregnant conditions in the simulation for the same body motion, it was found that the muscle load of the artificially-pregnant condition was 16% higher than that of the non-pregnant condition, and the muscle load of the pregnant condition was 50% higher than that of the non-pregnant condition.
The position and attitude controls of flapping wing flyers are challenging because of their inherent instabilities. Insects can cope with such difficulties by finely and quickly tuning their wing kinematics. In addition, it is known that insects change their posture through the joint between thorax and abdomen in response to visual stimuli. In this study, the effect of the body flexion on the flight dynamics of a hovering hawkmoth are investigated numerically by using an in-house computational fluid dynamics (CFD) and a flexible body dynamics (FBD) solvers. For an integrated understanding of the effects of the body flexion, the curved or flexible body models, which replicate the longitudinal active and passive body flexion respectively, are developed. Our computational results indicate that the slight change of the center of mass (CoM) caused by the active body flexion alters the total aerodynamic torque, which result in the large pitch-up or pitch down of the body within a few wingbeat cycles. It is also found that, even though the rigid body pitches up in free-flight with a measured wing kinematics, the mild flexibility in the body can maintain the body attitude without any control. These results point out the importance of the CoM position on the flight dynamics and control of a flapping flight and, furthermore, the possibility of the simple but effective flight-control system with the body flexion for a bio-inspired MAV.
The authors have proposed a technique for the laser bonding of bone with bioceramics sintered with hydroxyapatite and glass powders. This study aimed to investigate the effects of glass content in the bioceramics on the bonding strength and to verify the laser bonding between the bioceramics and the bone surface covered with periosteum. Five glass content conditions were examined: 20, 50, 60, 70, and 80 wt%. The bioceramic plate was positioned onto a bovine bone specimen, and a 5 mm diameter area was irradiated with a fiber laser beam in vitro. Every bioceramic specimen was instantaneously bonded to the bone specimen. Laser irradiation was performed with 400 W laser power and 1.0 s exposure time. The highest shear strength of the bonding between the bone and bioceramics was 12.4 ± 3.8 N at 20 wt% glass content in share fracture tests. The upper projected area of the bonding substance was the largest at 20 wt%, and there was a statistically positive correlation between the bonding strength and the projected area of the bonding substance. Furthermore, it was confirmed that the bioceramics instantaneously bonded to the bone surface covered with periosteum in vitro by laser irradiation using the same irradiation condition. The bioceramics, periosteum, and bone were melted, and a bonding substance was generated to bond both materials through the periosteum, thus suggesting the feasibility of the laser bonding method for clinical applications.