Nanoscale crack initiation and propagation in carbon fiber/epoxy composites using synchrotron: 3D image data.

Crack initiation and propagation in carbon fiber-reinforced plastic (CFRP) was observed under the application of an opening load using nanoscopic synchrotron radiation X-ray computed tomography (nanoscopic SR X-CT) at a high spatial resolution of ∼50 nm. Two datasets of reconstructed and segmented images were produced in typical regions, namely in the thin and thick epoxy regions where the resin thickness between the adjacent carbon fibers was small and large, respectively. This novel study presents the first non-destructive three-dimensional (3D) visualization of resin deformation behavior around crack tips, and provides a valuable and unique insight for the future design of CFRPs.

Effect of tensile force on the mechanical behavior of actin filaments.

Actin filaments are the most abundant components of the cellular cytoskeleton, and play critical roles in various cellular functions such as migration, division and shape control. In these activities, mechanical tension causes structural changes in the double-helical structure of the actin filament, which is a key modulator of cytoskeletal reorganization. This study performed large-scale molecular dynamics (MD) and steered MD simulations to quantitatively analyze the effects of tensile force on the mechanical behavior of actin filaments.

Modeling myosin-dependent rearrangement and force generation in an actomyosin network.

Actomyosin contractility is a major force-generating mechanism that drives rearrangement of actomyosin networks; it is fundamental to cellular functions such as cellular reshaping and movement. Thus, to clarify the mechanochemical foundation of the emergence of cellular functions, understanding the relationship between actomyosin contractility and rearrangement of actomyosin networks is crucial. For this purpose, in this study, we present a new particulate-based model for simulating the motions of actin, non-muscle myosin II, and α-actinin.

Effectiveness of scaffolds with pre-seeded mesenchymal stem cells in bone regeneration--assessment of osteogenic ability of scaffolds implanted under the periosteum of the cranial bone of rats.

To date, there has been no study on the development of novel regimens based on the following tissue engineering principles: seeding and culturing mesenchymal stem cells (MSCs) on a scaffold before surgery or injecting cultured MSCs into a scaffold during surgery. The purpose of this study was to assess the in vivo osteogenic ability of scaffold/MSCs implanted beneath the periosteum of the cranial bone of rats in three different sample groups: one in which MSCs were pre-seeded and cultured on a scaffold to produce the 3-D woven fabric scaffold/MSC composite using osteo-lineage induction medium, one in which cultured MSCs produced by osteo-lineage induction in cell cultivation flasks were injected into a scaffold during surgery and a control group, in which only the 3-D woven fabric scaffold was implanted. The results indicate that pre-seeding MSCs on a scaffold leads to a higher osteogenic ability than injecting cultured MSCs into a scaffold during surgery.

Simulations of dynamics of actin filaments by remodeling them in shear flows.

A mechanochemical relationship between intracellular flow fields of actin and remodeling of actin filaments is important to the realization of cell motility. In this study, to investigate this mechanochemical relationship, we present a mathematical model describing motions of actin filament and remodeling of the filaments in shear flows. We perform simulations of the dynamics of actin filaments remodeled by polymerization, depolymerization, and severing, and investigate contributions of these remodeling processes to effective shear viscosities of the system.

Evaluation of extensional and torsional stiffness of single actin filaments by molecular dynamics analysis.

It is essential to investigate the mechanical behaviour of cytoskeletal actin filaments in order to understand their critical role as mechanical components in various cellular functional activities. These actin filaments consisting of monomeric molecules function in the thermal fluctuations. Hence, it is important to understand their mechanical behaviour on the microscopic scale by comparing the stiffness based on thermal fluctuations with the one experimentally measured on the macroscopic scale.

Trabecular bone remodelling simulation considering osteocytic response to fluid-induced shear stress.

In bone functional adaptation by remodelling, osteocytes in the lacuno-canalicular system are believed to play important roles in the mechanosensory system. Under dynamic loading, bone matrix deformation generates an interstitial fluid flow in the lacuno-canalicular system; this flow induces shear stress on the osteocytic process membrane that is known to stimulate the osteocytes. In this sense, the osteocytes behave as mechanosensors and deliver mechanical information to neighbouring cells through the intercellular communication network.

Direct 3-D morphological measurements of silicone rubber impression using micro-focus X-ray CT.

Three-dimensional computer models of dental arches play a significant role in prosthetic dentistry. The microfocus X-ray CT scanner has the advantage of capturing precise 3D shapes of deep fossa, and we propose a new method of measuring the three-dimensional morphology of a dental impression directly, which will eliminate the conversion process to dental casts. Measurement precision and accuracy were evaluated using a standard gage comprised of steel balls which simulate the dental arch.

Estimation of bone permeability considering the morphology of lacuno-canalicular porosity.

Load-induced interstitial fluid flow in lacuno-canalicular porosity is believed to play an important role in cellular activities regulating adaptive bone remodeling. To investigate interstitial fluid behavior based on poroelasticity, it is important to determine the anisotropic permeability tensor reflecting the morphological features of the lacuno-canalicular porosity as fluid channels. In this study, we presented an estimation method of trabecular permeability by describing the analytical relationship between the volume orientation (VO) fabric tensor, which represents the canalicular orientation, and the permeability tensor.

Dynamic coupling between actin network flow and turnover revealed by flow mapping in the lamella of crawling fragments.

Dynamic turnover and transport of actin filament network is essential for protrusive force generation and traction force development during cell migration. To elucidate the dynamic coupling between actin network flow and turnover, we focused on flow dynamics in the lamella of one of the simplest but elegant motility systems; crawling fragments derived from fish keratocytes. Interestingly, we show that actin network in the lamella of fragments is not stationary as earlier reported, but exhibits a flow dynamics that is strikingly similar to that reported for higher order cells, suggesting that network flow is an intrinsic property of the actin cytoskeleton that is fundamental to cell migration.

Asymmetric intercellular communication between bone cells: propagation of the calcium signaling.

Bone functional adaptation by remodeling is achieved by harmonized activities of bone cells in which osteocytes in the bone matrix are believed to play critical roles in sensing mechanical stimuli and transmitting signals to osteoclasts/osteoblasts on the bone surface in order to regulate their bone remodeling activities through the lacuno-canalicular network with many slender osteocytic processes. In this study, we investigated the intercellular communication between bone cells, particularly focusing on its directionality, through in vitro observations of the calcium signaling response to mechanical stimulus and its propagation to neighboring cells (NCs). Direct mechanical stimulus was applied to isolated bone cells from chick calvariae, osteocytes (Ocys) and bone surface cells (BSCs) mainly containing osteoblasts, and the percentage of calcium signaling propagation from the stimulated cell to NCs was analyzed.

Coarse-grained modeling and simulation of actin filament behavior based on Brownian dynamics method.

The actin filament, which is the most abundant component of the cytoskeleton, plays important roles in fundamental cellular activities such as shape determination, cell motility, and mechanosensing. In each activity, the actin filament dynamically changes its structure by polymerization, depolymerization, and severing. These phenomena occur on the scales ranging from the dynamics of actin molecules to filament structural changes with its deformation due to the various forces, for example, by the membrane and solvent.

Actomyosin contractility spatiotemporally regulates actin network dynamics in migrating cells.

Coupling interactions among mechanical and biochemical factors are important for the realization of various cellular processes that determine cell migration. Although F-actin network dynamics has been the focus of many studies, it is not yet clear how mechanical forces generated by actomyosin contractility spatiotemporally regulate this fundamental aspect of cell migration. In this study, using a combination of fluorescent speckle microscopy and particle imaging velocimetry techniques, we perturbed the actomyosin system and examined quantitatively the consequence of actomyosin contractility on F-actin network flow and deformation in the lamellipodia of actively migrating fish keratocytes.

Osteocyte calcium signaling response to bone matrix deformation.

Osteocytes embedded in calcified bone matrix have been widely believed to play important roles in mechanosensing to achieve adaptive bone remodeling in a changing mechanical environment. In vitro studies have clarified several types of mechanical stimuli such as hydrostatic pressure, fluid shear stress, and direct deformation influence osteocyte functions. However, osteocyte response to mechanical stimuli in the bone matrix has not been clearly understood.

Calcium response in single osteocytes to locally applied mechanical stimulus: differences in cell process and cell body.

It is proposed that osteocytes embedded in the bone matrix have the ability to sense deformation and/or damage to the matrix and to feed these mechanical signals back to the adaptive bone remodeling process. When osteoblasts differentiate into osteocytes during the bone formation process, they change their morphology to a stellate form with many slender processes. This characteristic cell shape may underlie the differences in mechanosensitivity between the cell processes and cell body.

Wall boundary model for primitive chain network simulations.

In condensed polymeric liquids confined in slit channels, the movement of chains is constrained by two factors: entanglement among the chains and the excluded volume between the chains and the wall. In this study, we propose a wall boundary (WB) model for the primitive chain network (PCN) model, which describes the dynamics of polymer chains in bulk based on coarse graining upon the characteristic molecular weight of the entanglement. The proposed WB model is based on the assumptions that (i) polymers are not stuck but simply reflected randomly by the wall, and (ii) subchains below the entanglement length scale behave like those in bulk even near the wall.

Computer simulation of trabecular remodeling in human proximal femur using large-scale voxel FE models: Approach to understanding Wolff's law.

Ever since Julius Wolff proposed the law of bone transformation in the 19th century, it has been widely known that the trabecular structure of cancellous bone adapts functionally to the loading environment. To understand the mechanism of Wolff's law, a three-dimensional (3D) computer simulation of trabecular structural changes due to surface remodeling was performed for a human proximal femur. A large-scale voxel finite element model was constructed to simulate the structural changes of individual trabeculae over the entire cancellous region.

Strain field in actin filament network in lamellipodia of migrating cells: implication for network reorganization.

Cell motility is spatiotemporally regulated by interactions among mechanical and biochemical factors involved in the regulation of cytoskeletal actin structure reorganization. Although the molecular mechanisms underlying cell motility have been well investigated, the contributions of mechanical factors such as strain in the network reorganization remain unclear. In this study, we have quantitatively evaluated the strain field in the actin filament network forming the lamellipodia of migrating fish keratocytes to elucidate the mechanism by which actin filament network reorganization is regulated by biomechanical factors.

Simultaneous observation of calcium signaling response and membrane deformation due to localized mechanical stimulus in single osteoblast-like cells.

Biochemical signals related to a mechanosensory mechanism by which cells sense mechanical stimuli have been gradually clarified by biological approaches such as blocking specific signaling pathways; however, mechanical signals such as deformation/strain, which is transduced into biochemical signals through this mechanism, particularly at the cellular structural component level in a single cell, have not yet been clearly understood. This in vitro study focuses on an intracellular calcium signaling response to an applied localized deformation in a single osteoblast-like MC3T3-E1 cell, and observed localized deformation of a cell membrane and the calcium ion flux from an extracellular medium. The localized deformation was applied to a cell by indenting a microsphere onto the cell membrane using a glass microneedle.

Measurement of local strain on cell membrane at initiation point of calcium signaling response to applied mechanical stimulus in osteoblastic cells.

In adaptive bone remodeling, it is believed that bone cells such as osteoblasts, osteocytes and osteoclasts can sense mechanical stimuli and modulate their remodeling activities. However, the mechanosensing mechanism by which these cells sense mechanical stimuli and transduce mechanical signals into intracellular biochemical signals is still not clearly understood. From the viewpoint of cell biomechanics, it is important to clarify the mechanical conditions under which the cellular mechanosensing mechanism is activated.

Effects of post-training lesions in the hippocampus and the parietal cortex on idiothetic information processing in the rat.

Dead reckoning can be defined as the ability to navigate using idiothetic information based on self-movement cues without using allothetic information such as environmental cues. In the present study, we investigated the effects of hippocampal and parietal cortex lesions on homing behavior using dead reckoning in rats. Experimentally naive Wistar rats were trained with a homing task in which rats were required to take a food pellet from a cup in the arena and to return home with the pellet.

Framework for optimal design of porous scaffold microstructure by computational simulation of bone regeneration.

In bone tissue engineering using a biodegradable scaffold, geometry of the porous scaffold microstructure is a key factor for controlling mechanical function of the bone-scaffold system in the regeneration process as well as after the regeneration. In this study, we propose a framework for the optimal design of the porous scaffold microstructure by three-dimensional computational simulation of bone tissue regeneration that consists of scaffold degradation and new bone formation. The rate of scaffold degradation due to hydrolysis, that leads to decrease in mechanical properties, was simply assumed to relate to the water content diffused from the surface to the bulk material.