Surface topography and intracellular organization of human cells in suspension as revealed by scanning electron microscopy

This report presents a new procedure to study the ultrastructure of human cells in suspension by means of scanning electron microscopy. Living cells were maintained in suspension within cell culture flasks located on a rotating tilting table within an incubator. These cells were injected into warm glutaraldehyde/formaldehyde fixative. After washing in buffer, fixed cells were attached to propylamine-derived glass carriers. However, saturating free aldehyde groups of fixed cells and blocking amine groups of the derived glass carriers prevented cells from attachment to these carriers. Thus, we postulated that bonds between the fixed cell-free aldehyde groups and the carrier amine groups were responsible for cell-to-carrier attachment. Fixed cells attached to the carriers were subsequently dehydrated, dried, and coated for surface topography studies. For studies of internal cell organization, these attached cells were immersed in agar or gelatin as extracellular embedments and infused with sucrose or polyvinyl-pyrrolidone as cryoprotectants. Cells then were frozen and fractured. Fractured cells were either thawed, dehydrated, critical point dried, and ion beam sputter-coated, or freeze-substituted, dried, and planar magnetron sputter-coated. Finally, cell preparations were observed in the scanning electron microscope. Due to high cell attachment yield, both approaches samples observed in the electron microscope were representative of the entire cell population.     

Friction and wear behavior of aluminum-graphite composites as a function of interface and fiber direction

The friction and wear behavior of aluminum-graphite fiber composites was examined as a function of the interfacial reaction zone. Sliding wear tests were performed on three different fiber orientations on a standard pin-on-disk tribology machine. The counterface was made of gray cast iron with a surface hardness of 92 HRB. The wear rate and friction coefficient were found to decrease exponentially with sliding time and eventually reached a steady state condition. This was attributed to the development of a lubricating transfer film on the sliding surface. The wear mechanism was investigated through the use of scanning electron microscopy analysis. A wear model was developed for specimens worn with fibers parallel to the sliding direction. This model incorporates three dominant wear mechanisms: (1) matrix removal by delamination, (2) fiber wear due to plowing and (3) fiber pull-out. The model was evaluated numerically and was found to agree with the experimental data. The model predicts that whenever fiber pull-out is a contributing mechanism in the wear, the wear rate is an exponential function of the normal load. In contrast, the wear rate of composites is proportional to the normal load in the absence of fiber pull-out.     

Diffusion as a model of formation and development of surface topography

Changes of surface topography in tribological systems are due to inelastic processes as plastic deformation, detaching of wear particles and their reintegration into the surfaces. Due to these processes, the material particles are transported either along a surface or from one tribological partner to the other. Both processes are due to random interactions between surface asperities and are stochastic processes. The stochastic mass transfer between the surfaces is interpreted and described in the paper as a random deposition, the transport along a surface as a `diffusion' processes with some effective diffusion coefficient. We consider the development of the surface topography due to the described two kinds of random processes. There exist some stationary (in statistical sense) random surface topography with a power spectrum (spectral density) typical for many real frictional surfaces. The parameters of the model can either be obtained from comparison with measured topography or extracted from simulations at a lower space scale. The proposed mass transport model further allows to determine the wear rate in the system.     

Biomechanical, morphological, and histological analysis of early failures in hip resurfacing arthroplasty

The present revival of hip resurfacing arthroplasty may be related to an increase in early failures owing to the challenging technique of the procedure. Fifty-five retrieved implants were analysed with respect to wear, cement mantle and cement penetration, fracture and head morphology, as well as standard histology. Femoral neck fractures occurred in median after 102 days. The time to failure was shorter for older women. Major deviations from the suggested cement mantle thickness and cement penetration were found. Indications for high trauma during implantation leading to early failure due to weakening of the femoral neck were also observed. Some failures had signs of pseudarthrosis beneath the implant. Four different fracture patterns with different mean survival times were identified. Observed wear was minor with the exception of that due to alignment mistakes (rim loading). The cups were not damaged by the failures. Histological results indicate that avascular necrosis is not necessarily connected with this kind of endoprosthetic surgery. Most of the failures analysed can probably be attributed to the 'learning curve' effect, which is an unsatisfactory situation.     

Confocal microscopy as a tool for the study of the intranuclear topography of chromosomes

A scanning confocal microscope was used to investigate the spatial positions of specific regions within blood cell nuclei. These centromeric regions were fluorescently labelled by in-situ hybridization to suspended nuclei with a centromere-1-specific DNA probe. The 3-D image data sets, obtained by optical sectioning of the cells, were used to determine the spatial position of the centromeric regions in the nuclei by means of specially developed software. The centromeres were found to be localized near the nuclear boundary. This spatial pattern was tested against a random distribution model by means of the Kolmogorov—Smirnov test. The difference between the two patterns was at a P < 0?01 significance level.     

Effect of surface topography on the frictional behavior at the micro/nano-scale

In this paper, the effect of surface topography on the frictional behavior is investigated at micro/nano-scale in order to better understand the influence of asperity contact angle on friction. Experiments were performed to observe the variation in the frictional force as a spherical ball slides across a grooved surface. Specimens with single and multiple grooves of tens of micrometers in width were fabricated on silicon wafers. The frictional behavior between these specimens and steel balls of different diameters were observed with a tribometer built inside a scanning electron microscope (SEM). Normal load in the range of 20 mN and sliding speed of about 1-6 μm/s were applied in the experiments. It was shown that for relative ball/groove dimension that resulted in low contact angle, the overall frictional force was less than that observed for surface without the groove. Also, in situations where there was a great change in the contact angle stick-slip behavior could be observed. This stick-slip behavior is attributed to mechanical interlocking action.In addition to the above experiments, tests were conducted using lateral force microscopy (LFM). Unlike the previous finding that LFM output is dependent on the slope alone, it was found that the signal was more sensitive to the change in slope, especially when the slope was relatively large. Overall, both micro and nano-scale topographic effect on friction was similar. These results will ultimately aid in design of surface topography for micro-systems for best tribological performance.     

角膜地形图仪中调焦函数的选取及搜索方法

选取适合角膜地形图仪的调焦函数并设计搜索方法。基于角膜地形图仪的图像拍摄要求及调焦系统原理,采用八种调焦评价函数对实验图像进行处理,对比分析不同调焦函数的单峰性、一致性、灵敏度、计算速度等指标。结果显示:除了Variance函数的单峰性较差,其他七种函数都有良好的单峰性、一致性和计算速度,而Laplacian函数灵敏度最高,有效测量范围小,适合精确调焦;NRSS函数灵敏度低,有效测量范围大,适合粗调焦。基于所选取的调焦评价函数,针对角膜地形图仪调焦系统,设计了一种基于阈值判别条件的搜索方法,确定其调焦阈值,并通过实验验证该方案的有效性。     

Surface topography of cylinder bores — the relationship between manufacture,characterization and function

Much work has been undertaken in recent years into the understanding of surface topography, although to date the relationship between manufacturing, characterization and function is little understood. Initially in this paper attempts are made to relate the three facets together and then a selection of suitable parameters which may be used for characterization in relation to a range of functional needs required of engineering surfaces are selected.The significance of appropriate characterization is demonstrated by reference to machining, initial “running-in” and subsequent wear of cylinder bores of internal combustion engines.     

Tribological behavior of graphite-containing nickel-based composite as function of temperature,load and counterface

Nickel-based graphite-containing composites were prepared by powder metallurgy method. Their mechanical properties at room temperature and friction and wear properties from room temperature to 600 °C were investigated by a pin-on-disk tribometer with alumina, silicon nitride and nickel-based alloy as counterfaces. The effects of graphite addition amount, temperature, load, sliding speed and counterface materials on the tribological properties were discussed. The micro-structure and worn surface morphologies were analyzed by scanning electron microscope (SEM) attached with energy dispersive spectroscopy (EDS). The results show that the composites are mainly consisted of nickel-based solid solution, free graphite and carbide formed during hot pressing. The friction and wear properties of composites are all improved by adding 6–12 wt.% graphite while the anti-bending and tensile strength as well as hardness decrease after adding graphite. The friction coefficients from room temperature to 600 °C decrease with the increase of load, sliding speed while the wear rates increase with the increasing temperature, sliding speed. The lower friction coefficients and wear rates are obtained when the composite rubs against nickel-based alloy containing molybdenum disulfide. Friction coefficients of graphite-containing composites from room temperature to 600 °C are about 0.4 while wear rates are in the magnitude of 10^?5 mm³/(N m). At high temperature, the graphite is not effective in lubrication due to the oxidation and the shield of ‘glaze’ layer formed by compacting back-transferred wear particles. EDS analysis of worn surface shows that the oxides of nickel and molybdenum play the main role of lubrication instead of graphite at the temperature above 400 °C.     

X‐ray CT and histological imaging of xylem vessels organization in Mimosa pudica

Mimosa pudica has three distinct specialized organs, namely, pulvinus, secondary pulvinus, and pulvinule, which are respectively controlling the movements of petioles, leaflets, and pinna in response to external stimuli. Water flow is a key factor for such movements, but detailed studies on the organization of the vascular system for water transport in these organs have not been published yet. In this study, organizations of the xylem vessels and morphological features of the pulvinus, the secondary pulvinus, and the pulvinule were experimentally investigated by X‐ray computed tomography and histological technique. Results showed that the xylem vessels were circularly distributed in the specialized motile organs and reorganized into distinct vascular bundles at the extremities. The number and the total cross‐sectional area of the xylem vessels were increased inside the specialized motile organs. Morphological characteristics obtained in this study provided new insight to understand the functions of the vascular networks in the dynamic movements of M. pudica. Microsc. Res. Tech. 76:1204–1212, 2013. © 2013 Wiley Periodicals, Inc.     

The role of TiO2 nanotube surface on osseointegration of titanium implants: Biomechanical and histological study in rats

The nanoscale surface of titanium has been studied to improve the cellular recognition of the biological microenvironment and to increase bone–implant interaction. The aim of this study was to analyze the effect of a titanium oxide (TiO₂) nanotube surface with a machined surface on osseointegration tibia implants without primary stability. This study used an experimental design, divided into two groups (n = 16): commercially pure titanium machined implants (Cp‐Ti Ma) and commercially pure titanium anodized implants (Cp‐Ti An). Titanium nanotubes were produced by anodic oxidation, and the topography of surface was analyzed using field emission scanning microscope (FE‐SEM). The implants (2.1 × 2.8 mm Ø) were surgically placed in the right tibia (defects with milling drill 2.5 × 3.2 mm Ø) of 32 Wistar male rats (250–300 g). The animals were euthanized at 7 weeks postoperatively. The maximum value of removal torque was measured (N/cm) in the right tibia half of each group (8 animals/8 tibiae); the other half of each group underwent a nondecalcified protocol, stained with Stevenel blue/Alizarin red, and the formation of bone tissue in close contact to the implant was measured. The obtained data were analyzed statistically (t test). Differences were considered statistically significant for α < 0.05. Cp‐Ti An implants were significantly higher in removal torque and peri‐implant bone healing compared with Cp‐Ti Ma implants (p < .01). Within the limitations of this study, it was observed that the surface modification of titanium by anodization (TiO₂ nanotubes) can improve osseointegration, and this may be very useful to reduce the time required for peri‐implant bone formation.     

Influence of counter surface topography on the tribological behavior of carbon-filled PPS composites in water

This study is aimed at investigating the influence of counter surfaces׳ topography on tribological behavior of several carbon-filled polyphenylene sulfide (PPS) composites in water lubricated contacts. The results of this study showed significant increase in wear rate of pure, graphite and/or multi-walled carbon nanotubes filled PPS composites with increase in mean slope of profile along the sliding direction (Δα_y). This is while SCF filled PPS composites exhibited 1–3 orders of magnitude lower wear rate with little dependence on counter surface roughness characteristics. Among the roughness parameters studied, R_pk and lay orientation played a more significant role in friction, and R_pk and Δα_y were found to correlate best with the wear rate of the composites not containing SCF in their matrices.     

New anti-actin drugs in the study of the organization and function of the actin cytoskeleton.

The high degree of structural and molecular complexity of the actin-based cytoskeleton, combined with its ability to reorganize rapidly and locally in response to stimuli, and its force-generating properties, have made it difficult to assess how the different actin structures are assembled in cells, and how they regulate cell behavior. An obvious approach to study the relationships between actin organization, dynamics, and functions is the specific perturbation of actin structures using pharmacological means. Until recently there were only a few agents available that interfered with cellular activities by binding to actin and most of our knowledge concerning the involvement of actin in basic cellular processes was based on the extensive use of the cytochalasins. In recent years we have identified an increasing number of actin-targeted marine natural products, including the latrunculins, jasplakinolides (jaspamides), swinholide A, misakinolide A, halichondramides, and pectenotoxin II, which are discussed in this article. All these marine-sponge-derived compounds are unusual macrolides and can be classified into several major families, each with its own distinct chemical structures. We describe the current state of knowledge concerning the actin-binding properties of these compounds and show that each class of drugs alters the distribution patterns of actin in a unique way, and that even within a chemical class, structurally similar compounds can have different biochemical properties and cellular effects. We also discuss the effects of these new drugs on fenestrae formation in liver endothelial cells as an example of their usefulness as powerful tools to selectively unmask actin-mediated dynamic processes.     

谈单位工程施工组织设计在施工中的作用

论述单位工程施工组织设计的内容及其在工程施工中的指导作用。所有建筑安装单位都必须认真编写施工组织设计。     

Measurement of lubricating film thickness,temperature and pressure in gear contacts with surface topography as a parameter

Thin film transducers, sputtered onto a tooth flank, are used to measure temperature, pressure and oil film thickness profiles in gear contact. The former two are resistance sensors, while the film thickness sensor functions as a capacitive transducer. Experiments were carried out with ground and hobbed gears. The measurements are repeated after the tooth flank has been polished. The differences of the measured values for the ‘rough’ and ‘smooth’ surfaces are used for comparisons between differently machined surfaces. An EHD simulation programme has been developed which calculates film thickness and contact pressure, also taking surface roughness into account.     

Cryo-electron diffraction as a tool to study local variations in the lipid organization of human stratum corneum

The human skin provides the body with a barrier against transepidermal water loss and the penetration of harmful agents (e.g. microbes) from outside. This barrier function is produced mainly by the outermost, nonviable layer of the epidermis, the stratum corneum (SC). The SC consists of terminally differentiated corneocytes surrounded by a continuous intercellular lipid domain, which contains mostly ceramides, cholesterol and free fatty acids. Small- and wide-angle X-ray diffraction studies have elucidated the lamellar and lateral lipid organizations in these domains. However, these techniques require bulk quantities of SC, as a result of which local structure information on the lipids cannot be obtained. Insights to these local lipid arrangements are important when new transdermal drug delivery systems have to be developed. Therefore, the technique of electron diffraction arose as a tool to study the lateral packing of the lipids in the intercellular domains of SC, locally. In a previous study, the suitability of electron diffraction was demonstrated using a lipid model system that resembled the lipid composition of the SC. The spacings calculated from the electron diffraction patterns were in good agreement with the spacings revealed by wide-angle X-ray diffraction. The results presented here succeed this previous study. We improved the microscope settings and developed a new preparation method to study ex vivo human SC by cryo-electron diffraction. The method is based on the conventional tape-stripping method and offers the possibility to study depth-related changes in the lipid organization of human SC. Diffraction patterns of both hexagonal and orthorhombic lipid lattices have been recorded with spacings that resembled those found in human SC by wide-angle X-ray diffraction. After lipid extraction, such diffraction patterns could no longer be detected in the samples.     

Biomechanical simulation of an amputated forearm with and without a prosthesis

In this study a computer simulation was developed for analysing the performance of a below-elbow amputated forearm, with and without a prosthesis. The upper extremity was represented in terms of two rigid bodies, the arm and the forearm. Five muscles, three elbow flexors and two elbow extensors, were included in the model. The muscle model used was the five-component model, including the contractile, parallel, series and viscous elements and the muscle mass. Dynamic and static simulations were conducted, with and without prosthesis, to study parametrically the effects of stump length, tendon distal transfer, tendon or muscle shortening and muscle physiological cross-sectional area. The performance measures which were the most affected included flexion moment of the forearm about the elbow, muscle moment, force in the joint, flexion rate and mechanical energy. The simulation presented an interesting case when the amputation site is more proximal than the anatomical insertion point of a muscle, necessitating shortening of the muscle to avoid the situation where it exerts no force. It was also found that, of the changeable parameters, the most beneficial changes in the forearm parameters for improved dynamic performance were: (a) tendon distal transfer and (b) increase of the muscle cross-sectional area, the latter achievable by means of physical training.