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At least 19 recordsLinked to original sources
PubMed2006

Adaptation of cellular mechanical behavior to mechanical loading for osteoblastic cells.

Numerous cellular biochemical responses to mechanical loading are transient, indicating a cell's ability to adapt its behavior to a new mechanical environment. Since load-induced cellular deformation can initiate these biochemical responses, the overall goal of this study was to investigate the adaptation of global, or whole-cell, mechanical behavior, i.e., cellular deformability, in response to mechanical loading for osteoblastic cells. Confluent cell cultures were subjected to 1 or 2 Pa flow-induced shear stress for 2 h. Whole-cell mechanical behavior was then measured for individual cells using an atomic force microscope. Compared to cells maintained under static conditions, whole-cell stiffness was 1.36-fold (p=0.006) and 1.70-fold (p<0.001) greater for cells exposed to 1 and 2 Pa shear loading, respectively. The increase in shear stress magnitude from 1 to 2 Pa also caused a statistically significant, 1.25-fold increase in cell stiffness (p=0.02). Increases in cell stiffness were not altered in either flow group for 70 min after flow was terminated (p=0.15). Flow-induced rearrangement of the actin cytoskeleton was also maintained for at least 90 min after flow was terminated. Taken together, these findings support the hypothesis that cells become mechanically adapted to their mechanical environment via cytoskeletal modifications. Accordingly, cellular mechanical adaptation may play a key role in regulation of cellular mechanosensitivity and the related effects on tissue structure and function.

3T3 Cells↗
PubMed1984

Rate dependency, behavioral mechanisms, and behavioral pharmacology.

Behavioral pharmacology has become increasingly independent of the experimental analysis of behavior. At its beginning, behavioral pharmacology was closely related to the experimental analysis of behavior, with developments in each field aiding the other. Early attempts to systematize data in behavioral pharmacology culminated with the development of the rate-dependency concept, but as this principle was found to have more limited generality than originally was hoped, a theoretical void developed. This circumstance was followed by increased reliance on pharmacological theory as a basis for experimentation and interpretation, with an attendant decrease in emphasis on environmental variables and behavioral interpretations. Lack of interplay between behavioral pharmacology and the experimental analysis of behavior is detrimental to both disciplines because each could contribute significantly to the other. The current trend might be reversed if more research were directed at elucidating behavioral mechanisms of drug action.

Animals↗
PubMed2000

Intermolecular forces in bovine serum albumin solutions exhibiting solidlike mechanical behaviors.

Mechanical properties of bovine serum albumin (BSA) solutions were analyzed to gain information on intermolecular forces that stabilize the system under normal physiological conditions. BSA solutions showed unexpectedly large zero shear viscosity values under steady shear flows but responded like solids to sinusoidal linear strains: the storage shear moduli were always larger than the loss shear moduli in the frequency range 1-100 rad/s. These results suggest that BSA solutions are so-called colloidal crystals in which colloidal particles are ordered in an array due to strong repulsive forces among particles. However, the pair potential between BSA molecules predicted based on the conventional Derjaguin-Landau-Verwey-Overbeek theory failed to explain these remarkable mechanical properties of BSA solutions. Additional repulsive forces other than electrostatic must be introduced to explain stability of BSA aqueous dispersions.

Algorithms↗
PubMed2005

The role of computational models in the search for the mechanical behavior and damage mechanisms of articular cartilage.

Articular cartilage plays a vital role in the function of diarthrodial joints. Due to osteoarthritis degeneration of articular cartilage occurs. The initial event that triggers the pathological process of cartilage degeneration is still unknown. Cartilage damage due to osteoarthritis is believed to be mechanically induced. Hence, to investigate the initiation of osteoarthritis the stresses and strains in the cartilage must be determined. So far the most common method to accomplish that is finite element analysis. This paper provides an overview of computational descriptions developed for this purpose, and what they can be used for. Articular cartilage composition and structure are discussed in relation with degenerative changes, and how these affect mechanical properties.

Animals↗
PubMed2006

The effects of morphology, confluency, and phenotype on whole-cell mechanical behavior.

Emerging evidence indicates that cellular mechanical behavior can be altered by disease, drug treatment, and mechanical loading. To effectively investigate how disease and mechanical or biochemical treatments influence cellular mechanical behavior, it is imperative to determine the source of large inter-cell differences in whole-cell mechanical behavior within a single cell line. In this study, we used the atomic force microscope to investigate the effects of cell morphological parameters and confluency on whole-cell mechanical behavior for osteoblastic and fibroblastic cells. For nonconfluent cells, projected nucleus area, cell area, and cell aspect ratio were not correlated with mechanical behavior (p>or=0.46), as characterized by a parallel-spring recruitment model. However, measured force-deformation responses were statistically different between osteoblastic and fibroblastic cells (p<0.001) and between confluent and nonconfluent cells (p<0.001). Osteoblastic cells were 2.3-2.8 times stiffer than fibroblastic cells, and confluent cells were 1.5-1.8 times stiffer than nonconfluent cells. The results indicate that structural differences related to phenotype and confluency affect whole-cell mechanical behavior, while structural differences related to global morphology do not. This suggests that cytoskeleton structural parameters, such as filament density, filament crosslinking, and cell-cell and cell-matrix attachments, dominate inter-cell variability in whole-cell mechanical behavior.

Animals↗
PubMed2006

Effects of loading rate on the mechanical behavior of a natural rigid composite.

The effects of loading rate variations on the stress-strain behavior, failure mechanisms, fracture modes, and energy-dissipating capability of the spicules of the sponge Euplectella aspergillum have been investigated. Comparisons were made with similar measurements on a silicate glass. It was concluded that the very thin (5-10nm) organic layers that are interspersed with thicker layers of hydrated silica in the concentric ring structure of the spicules strongly influence all aspects of the mechanical behavior.

Animals↗
PubMed2001

KO's and organisation of peptidergic feeding behavior mechanisms.

Feeding behavior results from complex interactions arising between numerous neuromediators, including classical neurotransmitters and neuropeptides present in hypothalamic networks. One way to unravel these complex mechanisms is to examine animal models with a deletion of genes coding for the different neuropeptides involved in the regulation of feeding. The aim of this review is to focus on feeding and body weight regulation in mice lacking neuropeptide Y (NPY), melanocortins (POMC), corticotropin-releasing hormone, melanin-concentrating hormone, or bombesin-like peptides respectively. The phenotypes, which relate to the deletion of gene coding for the peptides, rarely include changes in body weight and food intake, indicating therefore the existence of redundant mechanisms to compensate for the loss of the peptide. The phenotype is much more marked when the gene deletion is targeted towards the functioning of the peptidergic machinery, e.g. the receptors and especially the POMC and NPY receptors, as well as one subtype of bombesin receptor (BRS-3). These knockout models are also interesting when examining the role of environmental and social factors in the determination of feeding behavior. They have granted us better knowledge of all these integrated and complex mechanisms. Moreover, they are also valuable tools for pharmacological studies when specific antagonists are lacking. From the information obtained by the study of knockouts, it is possible to determine certain targets for selective drugs that could be efficient for the pharmacological treatment of obesity. However, at the present state of our knowledge, it seems necessary to target several peptides in order to get good results with weight loss. It will also be imperative to associate these multitherapies with changes in eating and behavioral habits, in order to obtain complete effectiveness and long-lasting results.

Animals↗
PubMed2006

Measurement and characterization of whole-cell mechanical behavior.

An understanding of whole-cell mechanical behavior can provide insight into cellular responses to mechanical loading and diseases in which such responses are altered. However, this aspect of cellular mechanical behavior has received limited attention. In this study, we used the atomic force microscope (AFM) in conjunction with several mechanical characterization methods (Hertz contact theory, an exponential equation, and a parallel-spring recruitment model) to establish a mechanically rigorous method for measuring and characterizing whole-cell mechanical behavior in the deformation range 0-500 nm. Using MC3T3-E1 osteoblasts, measurement repeatability was assessed by performing multiple loading cycles on individual cells. Despite variability in measurements, repeatability of the measurement technique was statistically confirmed. The measurement technique also proved acceptable since only 5% of the total variance across all measurements was due to variations within measurements for a single cell. The parallel-spring recruitment model, a single-parameter model, accurately described the measured nonlinear force-deformation response (R2>0.99) while providing a mechanistic explanation of whole-cell mechanical behavior. Taken together, the results should improve the capabilities of the AFM to probe whole-cell mechanical behavior. In addition, the success of the parallel-spring recruitment model provides insight into the micromechanical basis of whole-cell behavior.

Animals↗
PubMed1999

On the theory of behavioral mechanics.

The Theory of Behavioral Mechanics is the behavioral analogue of Newton's laws of motion, with the rate of responding in operant conditioning corresponding to physical velocity. In an earlier work, the basic relation between rate of responding and sessions under two FI schedules and over a range of commonly used session values had been shown to be a power function. Using that basic relation, functions for behavioral acceleration, mass, and momentum are derived here. Data from other laboratories also support the applicability of a power function to VI schedules. A particular numerical value is introduced here to be the standard reference value for the behavioral force under the VI-60-s schedule. This reference allows numerical values to be calculated for the behavioral mass and momentum of individual animals. A comparison of the numerical values of the momenta of two animals can be used to evaluate their relative resistances to change, e.g., to extinction, which is itself viewed as a continuously changing behavioral force being imposed on the animal. This overall numerical approach allows behavioral force-values to be assigned to various experimental conditions such as the evaluation of the behavioral force of a medication dosage.

Animals↗
PubMed2002

Comparison of the mechanical behavior of the lumbar spine following mono- and bisegmental stabilization.

OBJECTIVE: To determine whether the mechanical behavior of the entire lumbar spine differs following mono- and bisegmental stabilization. DESIGN: The mechanical behavior of the lumbar spine was studied using the finite element method. BACKGROUND: Nonunion is somewhat more frequent after bi- than after monosegmental stabilization of the spine. Little is known about differences between the mechanical behavior associated with these procedures. METHODS: A three-dimensional nonlinear finite element model of the lumbar spine with internal spinal fixators and bone grafts was used to study mechanical behavior after mono- and bisegmental fixation with and without stabilization of the bridged vertebra. Finite element analyses were performed to determine the influence of four different graft positions, five loading conditions, and six different pretensions in the longitudinal fixator rod. The following parameters were considered: the maximum contact pressure at the interface between the bone graft and vertebral body, the force transmitted by the bone graft, and the size of the contact area between the graft and the vertebral body. RESULTS: Our model shows no clear differences between mono- and bisegmental fixation. Additional stabilization of the bridged vertebra exerts a partly adverse influence on the parameters studied. Pretension in the bridged region has a strong effect on the mechanical behavior. CONCLUSIONS: The mechanical behavior of the lumbar spine after mono- and bisegmental stabilization is similar. Thus biological factors and the surgical procedure are probably decisive in determining the fusion rate. RELEVANCE: Knowledge of the mechanical behavior after stabilization of the spine may help to improve the fusion rate. Our results suggest that the mechanical factors studied have only a minor influence on fusion rate and that other factors, such as incomplete resection of cartilage plate and poor local blood supply, are more decisive.

Biomechanical Phenomena↗
PubMed2005

The relative contributions of different skin layers to the mechanical behavior of human skin in vivo using suction experiments.

Although the mechanical behavior of the top layer of the skin, the epidermis, is an important consideration in several clinical and cosmetic applications, there are few reported studies on this layer. The in vivo mechanical behavior of the upper skin layer (here defined as epidermis and papillar dermis) was characterized using a combined experimental and modeling approach. The work was based on the hypothesis that experiments with different length scales represent the mechanical behavior of different skin layers. Suction measurements with aperture diameters of 1, 2 and 6 mm were combined with ultrasound and optical coherence tomography to study the deformation of the skin layers. The experiments were simulated for small displacements with a two-layered finite element model representing the upper layer and the reticular dermis. An identification method compared the experimental and numerical results to identify the material parameters of the model. For one subject the whole parameter estimation procedure was completed, leading to a stiffness of C(10,ul) = 0.11 kPa for the top-layer and C(10,rd) = 0.16 MPa for the reticular dermis. This unexpected, extreme stiffness ratio of the material parameters let to convergence problems of the finite element software for most of the individuals.

Adult↗
PubMed2001

The sintering and mechanical behavior of hydroxyapatite with bioglass additions.

There is increasing interest in the potential of composites of hydroxyapatite with phosphate- or silicate-based bioactive glasses, and certain of these glass additions have been found, in previous work, to aid densification and form a mechanically-reinforced, bioactive material; in particular, large improvements in flexural strength and fracture toughness were obtained through the addition of small amounts of phosphate glass. Less is known about the mechanical behavior of HA/bioglass composites, although in vivo studies by other workers have shown encouraging biological results. In this investigation, the sintering behavior, mechanical properties, and microstructure of composites of HA with up to 50 wt % glass, were analyzed. X-ray diffraction showed the phase composition of sintered composites with up to 5 wt % added bioglass to be non-stoichiometric HA with alpha-TCP or beta-TCP. Phase analysis of composites containing higher glass additions was impracticable due to peak broadening and overlap, although reaction products, at the highest glass additions and sintering temperatures, may include wollastonite-2M and beta-Na2Ca4(PO4)2SiO4. Sintered density, and mechanical properties other than fracture toughness, showed no significant improvement over HA.

Journal Article↗
PubMed1994

The mechanical behavior and morphological structure of callus in experimental callotasis.

Experimental callotasis was made in rabbit femurs. In order to compare mechanical behaviors and morphological structure of callus in callotasis, mechanical tests and histological examination were performed. Twenty Japanese white male rabbits were used. The right femurs were osteotomized at the level of the midshaft with a rotary cutter and fixed with a mini-model external fixator. After a 5-day waiting period, bone lengthening was started at the rate of 0.25 mm two times a day. Animals were divided into four groups. Group 1 and Group 2 were continual distraction group, Group 3 and Group 4 discontinued distraction group. The viscoelastic property was demonstrated in continual distraction group irrespective of distraction period, we thought the central undifferentiated connective tissue in callus was mainly responsible for the mechanical behavior. On the other hand, in discontinued distraction group, viscoelastic property shifted to elastic property corresponding to the rest period, we thought this change of mechanical behavior was histologically owing to the replacement of undifferentiated connective tissue by cartilage and the partial union of bone in callus.

Animals↗
PubMed1991

Mechanical behavior of closed lamellar membranes as a possible common mechanism for the establishment of developmental shapes.

The mechanical behavior of a closed membrane composed of two layers in contact is described as it is obtained by finding the minimum of the membrane bending energy at constant membrane area, constant difference between the areas of the two layers, and constant enclosed volume. It is shown that the membrane bending energy is a discontinuous function of the volume (v) and difference between the layer areas (delta a) defined relative to the volume and area difference of a sphere with the same membrane area, respectively. However, for different classes of shapes it is possible to obtain regions in the v/delta a diagram within which the shapes change continuously with v and delta a. These regions are shown for the egg, dumbbell and cup shape classes, respectively. The results of the shape analysis are used in the discussion of cell polarity, cytokinesis and gastrulation. Cell polarity is related to the decrease in symmetry during the transition from the radially symmetrical spherical shape to the asymmetrical shapes of the egg class. It is proposed that symmetrical cytokinesis occurs within the dumbbell class and that asymmetrical cytokinesis occurs within the egg class. Gastrulation is described as shape transformations within the class of cup shapes.

Cell Division↗
PubMed2001

Influence of the selection of the suture material on the mechanical behavior of a biomaterial to be employed in the construction of implants. Part 1: Calf pericardium.

A hydraulic stress simulator was employed to study the mechanical behavior of the calf pericardium used in the construction of cardiac valve leaflets. One hundred eighty pairs of tissue samples were subjected to tensile testing to rupture. One of the two samples from each of 144 pairs (four series of 36 pairs each) was sutured with commercially available threads made of nylon, silk, Prolene or Gore-Tex, while the other sample in each of these pairs was left unsewn. The remaining 36 pairs were employed as controls in which neither of the two samples was subjected to suturing. The sutured tissue samples showed a significant decrease in tensile strength at rupture (range: 11.81 to 26.04 MPa) when compared with unsutured samples (range: 39.38 to 87.96 MPa; p < 0.01). The application of morphological and mechanical selection criteria to maximize the homogeneity of the samples provided excellent fit with respect to the stress/strain curves. This method made it possible to carry out a predictive study of the mechanical behavior of a sutured sample, based on that observed in the corresponding unsutured fragment. The interaction of the different suture materials with the pericardial tissue was also assessed by comparing the mechanical behavior of the sutured samples with that of the control samples. At stresses of less than 0.8 MPa, samples sewn with Gore-Tex were found to show the least difference with respect to the controls, indicating that this material presented the lowest degree of interaction with the pericardium. In conclusion, the degree of the loss of resistance to tearing of the sutured samples is of no value in the selection of the optimal suture material. The selection process applied makes it possible to predict the mechanical behavior in response to suturing of a given unsewn tissue specimen by determining that of its sutured mate. The similarity between the findings in samples sewn with Gore-Tex and in the unsutured controls indicates a lesser degree of interaction between the suture material and the pericardium employed in the construction of cardiac valve leaflets.

Animals↗
PubMed1984

Tolerance to N6-(L-phenylisopropyl) adenosine. Contribution of behavioral mechanisms and cross-tolerance profile.

The contribution of behavioral mechanisms to tolerance to N6-(L-phenylisopropyl)adenosine (L-PIA) was studied, along with the degree of cross-tolerance to other drugs active in the CNS. Rats were stabilized on a fixed-ratio of a 20 lever-pressing schedule for food reward and were then assigned to three daily-treatment groups. One group (saline-behavior associated) was injected with saline 15 min before the session, another (L-PIA-behavior associated) was injected with L-PIA (0.08 mg/kg) 15 min before the session and the last (L-PIA-behavior dissociated) was injected with L-PIA (0.08 mg/kg) immediately after the session. Tolerance developed to the decreasing effects of L-PIA on response rate in both groups, L-PIA-behavior associated and L-PIA-behavior dissociated. Behavioral mechanisms were thus not important in tolerance to L-PIA. In subsequent cross-tolerance tests, L-PIA-tolerant rats were cross-tolerant to the adenosine Al receptor agonist, N6-cyclohexyladenosine. The drugs 4,5,6,7-tetrahydroisoxazolo[5,4-c]pyridin-3-ol (THIP), diazepam, pentobarbital, ketamine, clonidine, d-amphetamine and caffeine did not produce differential effects in L-PIA-tolerant and non-tolerant subjects; however, L-PIA-tolerant subjects were more sensitive to the suppressive effects of chlorpromazine on the response-rate.

Adenosine↗
PubMed2005

Effects of aging on the mechanical behavior of human dentin.

An experimental study on the mechanical behavior of human dentin and the influence of age was conducted. Beams with rectangular cross-section were sectioned from the coronal dentin of virgin extracted molars (N = 76) that were obtained from (N = 70) patients between 17 and 80 years of age. The beams were loaded in either quasi-static 4-point flexure or 4-point flexural fatigue to failure and the stiffness, strength and fatigue properties were evaluated. In characterizing the fatigue response the beams were divided into two age groups that were regarded as young (17 < or = age < or = 30, mean +/- std. dev. = 25 +/- 5 years) and old (50 < or = age < or = 80, mean +/- std. dev. = 64 +/- 9 years) dentin. Results from monotonic loading showed that both the flexural strength and strain to fracture of dentin decreased significantly with age. The fatigue life of dentin increased with a reduction in cyclic stress amplitude and the fatigue strength of young dentin was greater than that of old dentin at all cyclic stress amplitudes. The endurance strength of young dentin (at 10(7) cycles) was approximately 44 MPa, whereas the old dentin exhibited an endurance strength of approximately 23 MPa. Based on differences in the mechanical behavior and microscopic features of the fracture surfaces from the young and old specimens, aging appears to result in an increase in both the rate of damage initiation and propagation in dentin.

Adolescent↗