Growth plate cartilage shows different strain patterns in response to static versus dynamic mechanical modulation

Longitudinal growth of long bones and vertebrae occurs in growth plate cartilage. This process is partly regulated by mechanical forces, which are one of the underlying reasons for progression of growth deformities such as idiopathic adolescent scoliosis and early-onset scoliosis. This concept of mechanical modulation of bone growth is also exploited in the development of fusionless treatments of these deformities. However, the optimal loading condition for the mechanical modulation of growth plate remains to be identified. The objective of this study was to evaluate the effects of in vitro static versus dynamic modulation and of dynamic loading parameters, such as frequency and amplitude, on the mechanical responses and histomorphology of growth plate explants. Growth plate explants from distal ulnae of 4-week-old swines were extracted and randomly distributed among six experimental groups: baseline (\(n=10\)), control (\(n=10\)), static (\(n=10\)) and dynamic (\(n=3\times 10\)). For static and dynamic groups, mechanical modulation was performed in vitro using an Indexed CartiGen bioreactor. A stress relaxation test combined with confocal microscopy and digital image correlation was used to characterize the mechanical responses of each explant in terms of peak stress, equilibrium stress, equilibrium modulus of elasticity and strain pattern. Histomorphometrical measurements were performed on toluidine blue tissue sections using a semi-automatic custom-developed MATLAB toolbox. Results suggest that compared to dynamic modulation, static modulation changes the strain pattern of the tissue and thus is more detrimental for tissue biomechanics, while the histomorphological parameters are not affected by mechanical modulation. Also, under dynamic modulation, changing the frequency or amplitude does not affect the biomechanical response of the tissue. Results of this study will be useful in finding optimal and non-damaging parameters for the mechanical modulation of growth plate in fusionless treatments.     

Force platform for rats measures fore and hind forces concurrently

Animal models are commonly used to test the efficacy of impact loading regimens on bone strength. We designed an inexpensive force platform to concurrently measure the separate peak vertical impact forces produced by the fore and hindfeet of immature F-344 rats when dropped onto the platform. The force platform consisted of three load cells placed in a triangular pattern under a flat plate. Rats were dropped from heights of 30, 45 and 60 cm onto the platform so that they landed on all four feet concurrently. The peak vertical impact forces produced by the feet of the rats were measured using a sampling frequency of 100 kHz. The location of each foot at landing relative to the load cells, and the force received by each load cell were combined in a series of static equations to solve for the vertical impact forces produced by the fore and hindfeet. The forces produced by feet when rats stood on the single platform were similarly determined. The forces exerted separately by the fore and hindfeet of young rats when landing on the plate as a ratio to standing forces were then calculated. Rats when standing bore more weight on their hindfeet but landed with more weight on their forefeet, which provides rationale for the greater response to landing forces of bones in the forelimbs than those in the hindlimbs. This system provided a useful method to simultaneously measure peak vertical impact forces in fore and hindfeet in rats.     

Picosecond dynamics of tyrosine side chains in proteins.

To probe the details of small amplitude motions in proteins, a dynamical analysis of the orientation fluctuations of two tyrosine side chains in the bovine pancreatic trypsin inhibitor is presented. Detailed results are given for the time history and correlation functions obtained for the ring motion from a molecular dynamics simulation of the entire protein. It is shown that even on a picosecond time scale orientational fluctuations of +/-30 degrees from the average position occur for the tyrosine rings in the interior of the protein. It is found that the Langevin equation is applicable to the ring torsional motion, which corresponds to that of an angular harmonic oscillator with near-critical damping. Two possible microscopic models for the observed damping effects are outlined. One of these, analogous to liquid behavior, is based on kinetic theory and takes account of the collisions which occur between atoms of the protein; the other, more analogous to solid behavior, involves the coupling among a large number of harmonic oscillators. The collisional model with parameters obtained from theoretical estimates leads to good agreement with the correlation functions from the dynamic simulation. However, the dephasing of harmonic oscillations can yield similar short-time results so that a distinction between the two models is difficult. The importance of damping effects on the motions involved in conformational transitions and enzymatic reactions is discussed.     

Negative-stain electron microscopy of inside-out FtsZ rings reconstituted on artificial membrane tubules show ribbons of protofilaments

FtsZ, the primary cytoskeletal element of the Z ring, which constricts to divide bacteria, assembles into short, one-stranded filaments in vitro. These must be further assembled to make the Z ring in bacteria. Conventional electron microscopy (EM) has failed to image the Z ring or resolve its substructure. Here we describe a procedure that enabled us to image reconstructed, inside-out FtsZ rings by negative-stain EM, revealing the arrangement of filaments. We took advantage of a unique lipid that spontaneously forms 500 nm diameter tubules in solution. We optimized conditions for Z-ring assembly with fluorescence light microscopy and then prepared specimens for negative-stain EM. Reconstituted FtsZ rings, encircling the tubules, were clearly resolved. The rings appeared as ribbons of filaments packed side by side with virtually no space between neighboring filaments. The rings were separated by variable expanses of empty tubule as seen by light microscopy or EM. The width varied considerably from one ring to another, but each ring maintained a constant width around its circumference. The inside-out FtsZ rings moved back and forth along the tubules and exchanged subunits with solution, similarly to Z rings reconstituted outside or inside tubular liposomes. FtsZ from Escherichia coli and Mycobacterium tuberculosis assembled rings of similar structure, suggesting a universal structure across bacterial species. Previous models for the Z ring in bacteria have favored a structure of widely scattered filaments that are not in contact. The ribbon structure that we discovered here for reconstituted inside-out FtsZ rings provides what to our knowledge is new evidence that the Z ring in bacteria may involve lateral association of protofilaments.     

Noctuid moths show neural and behavioural responses to sounds made by some bat-marking rings

Coloured rings are often used for marking bats so that specific individuals can be recognized. We noticed that the rings of mouse-eared bats, Myotis myotis and Myotis blythii, in a combination of one plastic-split and one metallic ring on the same forearm, emitted sounds that were largely ultrasonic each time the rings met in flight. We recorded the ring sounds and the echolocation calls produced by the bats, and played them back to neural preparations of lesser yellow underwing moths, Noctua comes, while making extracellular recordings from the moths' A1 auditory receptors. The peak energy of the ring sounds occurred much closer in frequency to the moth's best auditory frequency (the frequency at which the moth has the lowest auditory threshold) than the peak energy of the calls, for both bat species, and the ring sounds were detected at a threshold 5-6 dB peSPL lower than the calls. Moths performed evasive manoeuvres to playbacks of ring sounds more frequently than they did to control (tape noise) sequences. These neural and behavioural responses imply that certain bats should not be marked with two rings on one wing, as this may make the bat more apparent to tympanate insects, and may therefore reduce its foraging success. Copyright 1999 The Association for the Study of Animal Behaviour.     

Dynamic apical surface rings in superficial layer cells of koi Cyprinus carpio scale epidermis

This study examined the novel ring‐shaped structures found in the apical surface of individual cells of the scale epidermis of koi Cyprinus carpio. These apical rings are highly dynamic structures with lifetimes ranging from a few to several minutes. While several ring forms were observed, the predominant ring morphology is circular or oval. Two distinct ring forms were identified and designated type I and type II. Type I rings have a well‐defined outer border that encircles the surface microridges. Type II rings are smooth‐surfaced, dinner‐plate‐like structures with membranous folds or compressed microridges in the centre. Type II rings appear less frequently than type I rings. Type I rings form spontaneously, arising from swollen or physically interrupted microridges but without initially perturbing the encircled microridges. After persisting for up to several minutes the ring closes in a centripetal movement to form a circular or irregular‐shaped structure, the terminal disc. The terminal disc eventually disappears, leaving behind a submembranous vesicle‐like structure, the terminal body. Type I rings can undergo multiple cycles of formation and closing. Recycling epidermal apical rings form through centrifugal expansion from the terminal disc followed by apparent contraction back to the disc structure, whereupon the cycle may repeat or cease. The findings demonstrate a novel skin surface structure in fishes and are discussed with respect to communication with the external aqueous environment.     

Flow over a ski jumper in flight: Prediction of the aerodynamic force and flight posture with higher lift-to-drag ratio

Large eddy simulations (LESs) are performed to study the flow characteristics around two flight posture models of ski jumping. These models are constructed by three-dimensionally scanning two national-team ski jumpers taking flight postures. The drag and lift forces on each component of a ski jumper and skis (head with helmet and goggle, body, arms, legs and skis) and their lift-to-drag ratios are obtained. For the two posture models, the drag forces on the body, legs and skis are larger than those on the arms and head with helmet and goggle, but the lift forces on the body and skis are larger than their drag forces, resulting in high lift-to-drag ratios on the body and skis and low lift-to-drag ratio on the legs. We construct simple geometric models, such as the circular cylinder, sphere and thin rectangular plate, predicting the drag and lift forces on each component of a ski jumper and skis, and validate them with those obtained from LES. Using these geometric models, we perform a parametric study on the position angles of flight posture for higher total lift-to-drag ratio. The flight postures obtained increase the total lift-to-drag ratios by 35% and 21% from those of two base postures, respectively. Finally, LESs are performed for the postures obtained and show the increases in the total lift-to-drag ratios by 21% and 16%, respectively, indicating the adequacy of using the simple geometric models for finding a flight posture of ski jumping having a higher lift-to-drag ratio at low cost.     

Conversion of androstenedione and androstadienedione by sterol-degrading bacteria

The composition of steroid metabolites formed during the conversion of androstenedione and androstadienedione, products of degradation of sterol side chains by soil and mutant strains of the bacterial genera Mycobacterium and Protaminobacter, was studied. Testololactone was absent from the conversion products. This favors the idea of different cleavage pathways of steroid ring D in bacteria and fungi. Very small amounts of two new 14alpha-hydroxy derivatives with cleaved B ring were isolated after conversion of androstenedione by soil strains. It was shown that a mutant Mycobacterium smegmatis strain, as well as wild strains, could perform 14alpha-hydroxylation of steroids. It is suggested that cleavage of the steroid nucleus at the side of rings D and C starts with the introduction of a 14alpha-hydroxy group followed by dehydration.     

N+注入选育白腐菌及其降解油菜秸秆木质纤维素的研究

以白腐菌WY01为出发菌,利用N＋注入技术选育出一株遗传性状稳定的漆酶高产诱变菌株WY02,经过60 d的发酵培养,其产酶量由出发菌的13.75 U/g增加到52.5 U/g,即产酶量提高了2.82倍;诱变菌株WY02对油菜秸秆中的木质素、半纤维素和纤维素的降解率分别为54.1%,39.1%,32.8%,用红外光谱法（IR）分析经诱变菌株降解后的油菜秸秆中木质素官能团的变化,用于阐明诱变菌株对油菜秸秆中木质素的生物降解机制。结果表明：油菜秸秆经白腐菌诱变菌株降解后,其木质素含量明显降低。木质素与苯环相连的C=O键、木质素侧链上CH2结构以及木质素单体（紫丁香基和愈创木基）被部分降解,木质素的苯环结构遭到一定程度的破坏。     

Inside-out Z rings--constriction with and without GTP hydrolysis

The bacterial tubulin homologue FtsZ forms a ring-like structure called the Z ring that drives cytokinesis. We showed previously that FtsZ-YFP-mts, which has a short amphipathic helix (mts) on its C terminus that inserts into the membrane, can assemble contractile Z rings in tubular liposomes without any other protein. Here we study mts-FtsZ-YFP, where the membrane tether is switched to the opposite side of the protofilament. This assembled 'inside-out' Z rings that wrapped around the outside surface of tubular liposomes. The inside-out Z rings were highly dynamic, and generated a constriction force that squeezed the tubular liposomes from outside. This is consistent with models where the constriction force is generated by curved protofilaments bending the membrane. We used this system to test how GTP hydrolysis by FtsZ is involved in Z-ring constriction. Without GTP hydrolysis, Z rings could still assemble and generate an initial constriction. However, the constriction quickly stopped, suggesting that Z rings became rigidly stabilized in the absence of GTP hydrolysis. We propose that remodelling of the Z ring, mediated by GTP hydrolysis and exchange of subunits, is necessary for the continuous constriction.     

Evidence for a relatively random array of human chromosomes on the mitotic ring

We used fluorescence in situ hybridization (FISH) to study the positions of human chromosomes on the mitotic rings of cultured human lymphocytes, MRC-5 fibroblasts, and CCD-34Lu fibroblasts. The homologous chromosomes of all three cell types had relatively random positions with respect to each other on the mitotic rings of prometaphase rosettes and anaphase cells. Also, the positions of the X and Y chromosomes, colocalized with the somatic homologues in male cells, were highly variable from one mitotic ring to another. Although random chromosomal positions were found in different pairs of CCD-34Lu and MRC-5 late-anaphases, the separations between the same homologous chromosomes in paired late-anaphase and telophase chromosomal masses were highly correlated. Thus, although some loose spatial associations of chromosomes secondary to interphase positioning may exist on the mitotic rings of some cells, a fixed order of human chromosomes and/or a rigorous separation of homologous chromosomes on the mitotic ring are not necessary for normal mitosis. Furthermore, the relative chromosomal positions on each individual metaphase plate are most likely carried through anaphase into telophase.     

Mitral annuloplasty ring flexibility preferentially reduces posterior suture forces

Annuloplasty ring repair is a common procedure for the correction of mitral valve regurgitation. Commercially available rings vary in dimensions and material properties. Annuloplasty ring suture dehiscence from the native annulus is a catastrophic yet poorly understood phenomenon that has been reported across ring types. Recognizing that sutures typically dehisce from the structurally weaker posterior annulus, our group is conducting a multi-part study in search of ring design parameters that influence forces acting on posterior annular sutures in the beating heart. Herein, we report the effect of ring rigidity on suture forces. Measurements utilized custom force sensors, attached to annuloplasty rings and implanted in normal ovine subjects via standard surgical procedure. Tested rings included the semi-rigid Physio (Edwards Lifesciences) and rigid and flexible prototypes of matching geometry. While no significant differences due to ring stiffness existed for sutures in the anterior region, posterior forces were significantly reduced with use of the flexible ring (rigid: 1.95 ± 0.96 N, semi-rigid: 1.76 ± 1.19 N, flexible: 1.04 ± 0.63 N; p < 0.001). The ratio of anterior to posterior F_C scaled positively with increasing flexibility (p < 0.001), and posterior forces took more time to reach their peak load when a flexible ring was used (p < 0.001). This suggests a more rigid ring enables more rapid/complete force equilibration around the suture network, transferring higher anterior forces to the weaker posterior tissue. For mitral annuloplasties requiring ring rigidity, we propose a ring design concept to potentially disrupt this force transfer and improve suture retention.     

Electron microscopic study of cell surface rings during cell division and morphogenesis of Arthrobacter crystallopoietes.

The whole cell ultrastructure during cell division and morphogenesis of Arthrobacter crystallopoietes was monitored using electron microscopic techniques. Glucose-grown spherical cells were inoculated into succinate-based medium. In this medium, the organism undergoes a morphogenetic cycle consisting of elongation of spheres to rods, exponential growth as rods, and fragmentation of rods to spherical cells. Raised bands or rings that encircled the cells were evident on the cell surface of both sphere- and rod-shaped cells. Many rod-shaped cells possessed two or more rings arranged adjacent to each other in a parallel orientation. At each cell division a new ring was formed on both siblings. However, as predicted by the proposed model of unidirectional cell growth and by maintaining a ring from the previous generation, unequal numbers of rings were observed on sibling cells. Only one ring was visible on most of the spherical inoculum cells, but in some cases a second ring perpendicular to the other ring was observed. Parallel rings were found on spherical cells resulting from fragmentation or reductive cell division of rods during the stationary growth phase. Thus, these spheres could be distinguished from inoculum spheres containing a single ring or perpendicular orientation of rings. The number of rings per cell and arrangement of rings on the cell surface of sibling cells after cell division, but before cell separation, are discussed with respect to cell age, cell division, and sphere-rod-sphere morphogenesis of A. crystallopoietes.     

四氧嘧啶糖尿病大鼠主动脉零应力状态的变化

目的和方法：将沿径向切开的糖尿病大鼠及对照大鼠主动脉坏分别转正圩Ｋｒｅｂｓ液中,向其中分别加入缩血管物质及舒血管物质达各种浓度;观察其角度变化。用Ｓ－Ｐ法对大鼠主动脉壁肌动蛋白进行染色。结果：四氧嘧啶糖尿病大鼠病程４周时主动脉环展开角显著大于对照（Ｐ〈０．００１）。使用药物后大鼠主动脉坏展开角与使用前相比无明显差异（Ｐ〉０．０５）。糖尿病大鼠主动脉壁肌动蛋白色较对照组明显加深、染色的光密度显著大于     

A mechanical analysis of the relationship between free oscillations of Pinus pinaster Ait. saplings and their aerial architecture

The aim of this study was to investigate the influence of aerial architecture on the dynamic characteristics of young maritime pines (Pinus pinaster Ait.) using a mechanistic approach. For this purpose, three 4-year-old saplings with prominent differences in their branching patterns were submitted to free oscillation tests. The tests were carried out with different methods and directions of mechanical loading in order to initiate the movement of each sapling. The oscillations of the different architectural elements, i.e. stem and branches of different topological order, were measured with inclinometers and strain gauges fixed to saplings. Successive pruning of the architectural elements was carried out to evaluate their relative influence on the dynamic characteristics of the trees. The aerial systems were digitized before the mechanical tests in order to use 3D visualization techniques and to make architectural analyses of the crown structure. Two distinct modes of deformation were detected during free oscillations. The natural swaying frequency ranged from 0.6-0.8 Hz for the saplings tested at the same period of the year. The frequency variations were partly explained by the morphological differences of the experimental subjects. The motions of the axes were found to depend on their topology, i.e. the movement of the axes of a given branching order was forced by the movement of their respective bearing axis. The axes of third branching order had a significant and negative effect on the damping of the natural deformation mode. Results point out the major role played by foliage, qualitatively and quantitatively, on the damping of tree motions and on coupling the motions of the crown components.     

Podosome rings generate forces that drive saltatory osteoclast migration

Podosomes are dynamic, actin-containing adhesion structures that collectively self-organize as rings. In this study, we first show by observing osteoclasts plated on bead-seeded soft substrates that podosome assemblies, such as rings, are involved in tension forces. During the expansion of a podosome ring, substrate displacement is oriented outward, suggesting that podosomal structures push the substrate away. To further elucidate the function of forces generated by podosomes, we analyze osteoclast migration. Determining the centers of mass of the whole cell (G) and of actin (P), we demonstrate that osteoclasts migrate by "jumps" and that the trajectories of G and P are strongly correlated. The velocity of the center of mass as a function of time reveals that osteoclasts rapidly catch up with podosomal structures in a periodic pattern. We conclude that actin dynamics inside the cell are not only correlated with cell migration, but drive it.     

A femoral neck fracture model in rabbits

A technique was developed to create a reproducible femoral neck fracture in vitro using 5-month-old JW/CSK series male rabbits. Force attenuation of a newly developed damping material was also evaluated using this model. Ten pairs of the femora with smaller deviations in length and weight were harvested and cleaned of soft tissue. Either a right or left of each pair of the specimens was randomly selected and put into either the control or the experimental group, both of which contained equal numbers of the right and left femora. The specimens were attached to an L-shaped plate and embedded in a resin from the proximal diaphysis to the distal end so as to maintain a consistent position of the femora. They were mounted and fixed on a pedestal slanted in the coronal plane at 20 degrees. The impact load testing was conducted using an impact mallet dropped from a height of 3 cm. The impact load was applied onto the femoral head. To the specimens in the experimental group, attenuated impact forces were loaded through the damping material, but those in the control group were subjected to forces directly transmitted without the material. All the impact testing was performed in a temperature and humidity controlled chamber. All of the femoral specimens exposed to the direct impact forces (controlled group) sustained fracture at the neck. The fracture line passed from the base of the femoral head laterally and to the calcar area just proximal to the minor trochanter medially. The location of each fracture line was almost identical among the specimens. None of the specimens that were exposed to the impact force through the damping material (experimental group) sustained fracture macroscopically and roentgenographically.     

In vitro tracheal mechanics by nuclear magnetic resonance imaging

Images of rabbit tracheal cross sections were obtained at a series of transmural pressures ranging from 22 to -95 cmH2O by use of a nuclear magnetic resonance imaging microscope. The excised, washed tracheas were immersed in a solution of phosphate-buffered saline made up in deuterium oxide (D2O, pH 7.3). The images are maps of proton density in the image slice (2.5 mm thick). All but one series of images showed a collapse process in which the trachealis muscle invaginated asymmetrically, i.e., the muscle appeared to favor one side of the cartilage ring system more than the other. The connecting tissue between the cartilage rings appeared to be more compliant than the rings themselves, thus suggesting that the tracheal lumen became corrugated at negative pressures. In the plane of a cartilage ring, the lumen appeared to remain patent at pressures as low as -95 cmH2O. However, between rings, where the tracheal wall was more compliant, the lumen appeared to be totally occluded at -53 cmH2O. Lumen areas in both the plane of the cartilage rings and in a plane between rings were measured from each series of printed images for six tracheas. These measurements, when normalized, averaged, and plotted against transmural pressure gave asymptotic logarithmic compliances (n1 in the model of Lambert et al., J. Appl. Physiol. 52: 44-56, 1982) of 1.2 +/- 0.4 and 20 +/- 7 for the interring and ring regions, respectively. These values are greater than the critical value of 0.5 (J. Appl. Physiol. 62: 2426-2435, 1987) and are thus consistent with wave speed flow limitation being possible anywhere in the trachea during forced expiration.     

Effect of inflation on trachealis muscle tone in canine tracheal segments in vitro

Isolated tracheal segments were studied in vitro to determine how inflation affects the length and tension of the contracted and relaxed trachealis muscle. Circumferential trachealis muscle lengths were measured from cross-sectional radiographs taken during stepwise inflation of intact 20-cm-long tracheal segments to an inflation pressure of 25 cmH2O. A tracheal length spanning two cartilage rings was then cut out and mounted in a tissue bath using clips attached at the points of muscle insertion into the cartilage. The ring was stretched open along the axis of the muscle, and the resulting forces of the relaxed and contracted muscle and the cartilage were measured. Muscle lengths and tensions during inflation of the trachea were determined by comparing pressure vs. length and force vs. length measurements. During inflation from 0 to 25 cmH2O, the circumferential length of the trachealis muscle contracted with 10(-5) M acetylcholine increased from 48 to 70% of its length of maximal active tension (Lmax), while the relaxed muscle increased from 80 to 93% Lmax. The length of the contracted muscle was maintained at a nearly constant proportion of its relaxed length at each pressure.     

The distribution of protozoa among soil aggregates

Abstract The distribution of 5 groups of protozoan cells among soil aggregates from an arable field soil was investigated, by incubating each aggregate (1–2 mm) in a ring on an agar plate with a prey bacterium and detecting emergent-active forms of each group from respective aggregates. The detection of each protozoan group was especially affected by scattered times of the excystment and the rapid re-encystment owing to food exhaustion. The cumulative number of protozoan-positive rings obtained through observation at short time intervals, therefore, provided us with more reliable results.
It was shown that the distribution of protozoan cells was not even but greatly conglomerative among soil aggregates.