Direct Contact Area Research Articles

Spermatogonial stem cell organization in felid testis as revealed by Dolichos biflorus lectin.

Spermatogonial stem cells are being exploited in many species as a tool to recover fertility, but may also be used to manipulate the genetic pool. Whatever the purpose, these cells must be fully characterized and easily identifiable, and our goal was to improve this procedure in the domestic cat, used as an animal model for endangered felid species and for some human diseases/physiological processes. We have therefore screened several markers that might be used to distinguish and study the undifferentiated spermatogonia population insitu and invitro via immunohistochemistry applied to tissue sections and whole mounts of the domestic cat seminiferous tubules. Our results show that, although they label the cytoplasm and nucleus of gonocytes and spermatogonia in pre-pubertal animals, PGP9.5 and FoxO1 cannot be considered markers of undifferentiated spermatogonia in adult animals, as almost all spermatogonia, namely type A and B, express these proteins. Nonetheless, the Dolichos biflorus agglutinin (DBA lectin) was able to label the cell surface and cytoplasm of a small type A spermatogonial population in the adult animals. Analysis of the number and distribution of the DBA-labeled cells showed they were present in low number, which did not vary with epithelium seminiferous stage. Morphometric analysis revealed that DBA-labeled cells present tropism to a peculiar area of the seminiferous tubules, namely the area in direct contact with Leydig cells. Whole mounts of DBA-stained seminiferous tubules revealed the arrangement of DBA-stained cells in small clones up to eight cells. Noteworthy, the clonal cells presented variable staining intensity suggesting the existence of asymmetric distribution of O-glycosylated proteins within each clone. Our results strongly suggest that the DBA lectin is a marker of undifferentiated spermatogonia in domestic cat, and illustrate the peculiar characteristics of spermatogonial stem cell development and organization in this species.

Understanding the curvature effect of silica nanoparticles on lysozyme adsorption orientation and conformation: a mesoscopic coarse-grained simulation study.

In nanobiotechnology applications, curvature of nanoparticles has a significant effect on protein activities. In this work, lysozyme adsorption on different-sized silica nanoparticles (SNPs) was simulated at the microsecond timescale by using mesoscopic coarse-grained molecular dynamics simulations. It is found that, with the increase of nanoparticle size, which indicates a decrease of surface curvature, adsorbed lysozyme shows a narrower orientation distribution and a greater conformation change, as the electrostatic attraction dominates lysozyme adsorption, and this trend is more pronounced on larger SNPs. Interestingly, the effect induced by different SNP surface curvatures is not related to the direct contact area between lysozyme and SNPs, but to the interfacial hydration layer above the silica surface, since a smaller curvature can lead to a stronger interfacial hydration and make the distribution of interfacial water molecules more ordered. Besides, at higher ionic strength, lysozyme conformation is less affected by strongly negatively charged SNPs, especially for larger nanoparticles. This work might shed some light on how to prepare protein coronas with higher bioactivities in nanobiotechnology.

Review : Thermal contact problems at cryogenic temperature

This paper addresses technical problems of thermal contact conductance or resistance which inevitably occurs in most cryogenic engineering systems. The main focus of this paper is to examine what kind of physical factors primarily influences the thermal contact resistance and to suggest how it can be minimized. It is a good practical rule that the contact surface must have sub-micron roughness level with no oxide layer and be thinly covered by indium, gold, or Apiezon-N grease for securing sufficient direct contact area. The higher contact pressure, the lower the thermal contact resistance. The general description of this technique has been widely perceived and reasonable engineering results have been achieved in most applications. However, the detailed view of employing these techniques and their relative efficacies to reduce thermal contact resistances need to be thoroughly reviewed. We should consider specific thermal contact conditions, examine the engineering requirements, and execute each method with precautions to fulfil their maximum potentials.

An In Vitro Evaluation of Anterior, Lateral and Transforaminal Interbody Stabilization: Should Approach-Related Differences be a Consideration?

reactive tissue and osteoid. Proportion of the filling by these tissue types was variable between individuals and varied within portions of the PTN material. At 4 months, some areas of the inner pores were completely filled with bone suggesting new bone could form a complete bridge between the osteotomy sites with implant incorporated into this bony bridging. On average, 73.90% of the PTN pores were filled with bone þ fibrous tissue þ osteoid at 4-months, with two out of the four PTN devices having 100% of the pores being filled. At 4 and 6 month time points, perimeter surface area in direct contact with bone was greater for PTN compared to PEEK (23.90% vs 9.94% and 56.09% vs 27.31% at 6 months). In both 4 and 6 month time points, PTN had a single implant with bone apposition values of 72.58% and 77.48% respectively. CONCLUSIONS: Unlike PEEK, the novel PTN intervertebral fusion device tested in this study allowed for osseointegration of the implant surface adjacent to both endplates and osteoconduction within pores which has potential to improve overall spine fusion outcomes. FDA DEVICE/DRUG STATUS: Phusion Metal, PorOsteon, Inc. (Approved for this indication)

Histologic and Histometric Analysis of Bone Repair at the Site of Mandibular Body Osteotomy and at the Bone-Screw Interface After Using a Biodegradable 2.0-mm Internal Fixation System.

The aim of the study was to evaluate histologically and histometrically the bone repair at the mandibular body osteotomy and at the bone-screw interface after using a biodegradable 2.0-mm internal fixation system. Six dogs were subjected to an osteotomy in the mandibular body, which was stabilized by applying a fixation device manufactured with poly-L-DL-lactic acid (70:30). The dogs were euthanized at 2 and 18 weeks. Each screw was sectioned along its long axis, and the osteotomy sites were divided into 3 parts: the upper part was labeled the tension third (TT); the lower part, compression third (CT); and the part between the TT and CT, intermediary third (IT). Histologic analysis showed areas of direct contact between the screw surface and the parent lamellar bone at 2 weeks. At 18 weeks, 3 microscopically distinct layers at the bone-screw interface were noted. At the osteotomy sites, union between the bone fragments was observed at 18 weeks. Statistically significant differences in the newly formed bone among TT, IT, and CT (P = 0.019) were observed. In conclusion, the biomechanical environment created by the biodegradable IF system used in this study facilitated bone repair at the osteotomy site.

Study on the front contact mechanism of screen-printed multi-crystalline silicon solar cells

The two key issues of front contact of screen-printed multi-crystalline silicon have been studied. Firstly, the effects of doping profiles in the emitter on the contact-resistance have been systematically investigated. Constant source diffusion is used to explain the doped phosphorus profile in the textured emitter by simulation. Secondly, the penetration mechanism of silver into SiNx layer was studied by using SEM and EDX to reveal the microstructure of the Ag/Si contact. A model has been proposed to explain the formation of the ohmic contact. It is found that the effectiveness of the contact is determined by the direct contact area of the silver crystallites to both the emitter and the finger. For a commercial multi-crystalline silicon solar cell of 156×156mm2, the optimal contact-resistance of about 1.2mΩ is suggested, corresponding to the doping sheet resistance of around 80–90Ω/□. Multi-crystalline Si solar cells with excellent results, up to 18.51% in conversion efficiency, have been achieved. Moreover, to further understand the model, effects of the firing temperature and the thickness of SiNx layer on the contact-resistance have been investigated in the solar cells. It is proved that the formation of the silver crystallites is related to the existence of SiNx layer.

Metal migration at conductor / XLPE interface subjected to partial discharges at different electrical stresses

Metal migration effects occurring at the conductor/cross-linked polyethylene (XLPE) interface are presented in the paper. The phenomenon was studied under various electrical stresses: direct current, pulse-width modulated and sinusoidal. The comparison of aging effects on specimens subjected to the stimuli was presented. The electrical stress results in partial discharges, both around the electrode in the form of surface discharges and directly at the micro air gap interface between conductor and polymeric material. In order to isolate the impact of interface discharges, the surface effects were suppressed, eliminated and compared with results containing both forms of discharges. The electrical and thermal migration mechanism was investigated in the paper and assessment was performed by means of time to breakdown and both micro morphological and elemental analysis. Migration of the conductor atoms, where metallic particles are transferred to the insulating medium, was observed. Primarily, attention was afforded to the migration of copper and aluminum electrode atoms in two zones; one zone being the direct contact area at the interface and the second zone incorporating the area surrounding the electrode which is enhanced by surface discharges. A novel aspect relates to the investigation of the metal migration depth profile and the concentration intensity at different voltage stresses. The transport phenomena were analyzed with respect to both electrical and thermal mechanisms.

Preparation of bimetallic gold catalysts by redox reaction on oxide-supported metals for green chemistry applications

The major problem in successful preparation of bimetallic supported catalysts is the formation of an extended contact area between the monometallic phases. The selective deposition of Au on the surface of nanoparticles of a primary oxide-supported metal has been performed by a redox method that is based on the reduction of the second metal (M2) ions with hydrogen adsorbed on the surface of first metal (M1) or with M1 itself. The gold containing bimetallic catalysts with different atomic ratios and metal combinations Au–M1 (M1=Pd, Pt, Rh, Ru, and Au–RuOx) deposited on oxide supports (TiO2, SiO2 or θ-Al2O3) have been prepared by this method with special emphasis on the preparation of low-loaded gold containing bimetallic catalysts. The samples were characterized by X-ray diffraction analysis (XRD), scanning transmission electron microscopy (STEM), temperature programmed reduction (TPR) analysis, CO adsorption, X-ray photoelectron spectroscopy (XPS), Diffuse reflectance Fourier-transform IR spectroscopy of adsorbed CO (DRIFTS-CO). By varying the conditions of the preparation procedure, the direct contact area was obtained either between two metal phases (Au/M1) or between metal and a metal oxide phase (Au/M1Ox) that changed the catalytic properties of primary supported M1. The prepared bimetallic catalysts exhibited the high activity in various reactions: from the Cl-VOC oxidative degradation to the up-to-date “green” reactions aimed at the synthesis of fine chemicals from ethanol and glycerol.

Substrate Effect on the Refractive Index Sensitivity of Silver Nanoparticles

The bulk refractive index (RI) sensitivity of dispersed and immobilized silver nanoparticles of three different shapes (spheres, cubes, and plates) is investigated. We demonstrate, both experimentally and theoretically, that the influence of immobilization on the RI sensitivity is highly dependent on the shape of the nanoparticles. A strong correlation is seen between the fraction of the particle surface area in direct contact with the substrate and the decrease in RI sensitivity when the particles are immobilized on a glass substrate. The largest decrease (−36%) is seen for the most sensitive nanoparticles (plates), drastically reducing their advantage over other nanoparticle shapes. The shape-dependent substrate effect is thus an important factor to consider when designing nanoplasmonic sensors based on colloidal noble-metal nanoparticles.

Direct Radial LMHF Microvibration Induced Bone Formation and Promoted Implant Osseointegration

Mechanical loading is known to play an important role in bone remodeling. This study aimed to evaluate the effect of direct low-magnitude high-frequency (LMHF) microvibration on dental implant bone formation and osseointegration. Titanium implants were installed in rabbit tibiae. The implants in the left legs were loaded with mechanical vibration (15 μm) at 10, 20, 30, and 40 Hz (10, 20, 30, and 40 Hz groups, respectively) for 30 minutes every day. The implants on the right legs were used as a sham control and did not receive a vibration load. After 20 days, the 10, 20, and 30 Hz groups showed significantly greater newly formed bone volume, density, ratio of the bone surface area to the trabecular bone surface area, and ratio of the bone surface area in direct contact with osteoclasts versus the total bone surface area in the region of interest compared with the sham control group, especially the 20 Hz group. However, the 40 Hz group did not. In conclusion, the application of direct LMHF (10, 20, or 30 Hz) vibration on the implants promoted bone formation and osseointegration, especially at 20 Hz; however, the use of 40 Hz did not result in any significant improvement.

The jumbo cup: Curtain calls and caveats

Use of an oversized “jumbo cup” is an effective technique for revision of most failed acetabular components. The jumbo cup is prepared with hemispherical reamers and provides a large porous ingrowth surface area in direct contact with the host bone. However, since the oversized cup is larger than the native acetabulum, the hip center can be raised, which may require use of a longer femoral head to maintain soft tissue tension and leg length. The anterior edge of the cup may also protrude through the anterior wall, which could be a cause of iliopsoas tendonitis resulting in groin pain.

A study of charge transfer mechanism and optical properties of Au–CdS core–shell nanocrystals

The enhancement in band edge photoluminescence intensity and Purcell factor associated with red shift in PL features is observed in chemically prepared Au–CdS core–shell nanocrystals. The emission rate is increased by a factor 1.5 in case of Au–CdS core–shell nanocrystals compared to bare CdS nanocrystals, leading to the higher quantum yield. The magnitude of enhancement depends on the area of direct contact between Au and CdS nanocrystals, and hence on the interaction strength. These findings are understood on the basis of charge transfer and mixing of electron energy levels.

Design, Fabrication and Properties of Textured Self-Lubricated Tools in Dry Cutting

Textured self-lubricated tools were designed and fabricated. Dry cutting tests were carried out on with these self-lubricated tools and a conventional tool. The tool wear and the friction coefficient at the tool chip interface were measured. It was shown that the tool wear and the friction coefficient of the textured self-lubricated tools were reduced compared with that of the conventional tool. Two mechanisms responsible were found, the first one is explained as the formation of a lubricating film with low shear strength at the tool-chip interface, which was released from the texturing and smeared on the rake face, and served as lubricating additive during dry cutting; the other one was explained by the reduced contact length at the tool-chip interface of the textured tools, which contributes to the decrease of the direct contact area between the chip and rake face. It is suggested that the using of textured self-lubricated tools is an effective way to reduce the tool wear in dry cutting.

Binding Affinity Prediction for Protein–Ligand Complexes Based onβContacts and B Factor

Accurate determination of protein-ligand binding affinity is a fundamental problem in biochemistry useful for many applications including drug design and protein-ligand docking. A number of scoring functions have been proposed for the prediction of protein-ligand binding affinity. However, accurate prediction is still a challenging problem because poor performance is often seen in the evaluation under the leave-one-cluster-out cross-validation (LCOCV). We introduce a new scoring function named B2BScore to improve the prediction performance. B2BScore integrates two physicochemical properties for protein-ligand binding affinity prediction. One is the property of β contacts. A β contact between two atoms requires no other atoms to interrupt the atomic contact and assumes that the two atoms should have enough direct contact area. The other is the property of B factor to capture the atomic mobility in the dynamic protein-ligand binding process. Tested on the PDBBind2009 data set, B2BScore shows superior prediction performance to existing methods on independent test data as well as under the LCOCV evaluation framework. In particular, B2BScore achieves a significant LCOCV improvement across 26 protein clusters-a big increase of the averaged Pearson's correlation coefficients from 0.418 to 0.518 and a significant decrease of standard deviation of the coefficients from 0.352 to 0.196. We also identified several important and intuitive contact descriptors of protein-ligand binding through the random forest learning in B2BScore. Some of these descriptors are closely related to contacts between carbon atoms without covalent-bond oxygen/nitrogen, preferred contacts of metal ions, interfacial backbone atoms from proteins, or π rings. Some others are negative descriptors relating to those contacts with nitrogen atoms without covalent-bond hydrogens or nonpreferred contacts of metal ions. These descriptors can be directly used to guide protein-ligand docking.

Photopolymerizable phosphate acrylates as comonomers in dental adhesives with or without triclosan monomer units

Phosphate diacrylates (CO-DAP, TMP-DAP) based on castor oil or trimethylolpropane were synthesized and evaluated in dental adhesive formulations in comparison with 3-acryloyloxy-2-hydroxypropyl methacrylate phosphate (AMP-P). In an attempt to promote antibacterial activity, another photopolymerizable monomer (TCS-UMA) containing 5-chloro-2-(2,4-dichlorophenoxy)phenol moiety (triclosan) was prepared and incorporated in adhesive resins. Each of these monomers had a molecular structure confirmed by spectral methods. The photopolymerization rates for monomers (0.063–0.088s−1) were lower than those determined in the monomer combinations (0.116–0.158s−1) incorporating phosphate diacrylate (11wt.%), BisGMA (33wt.%), TEGDMA (10wt.%), UDMA (10wt.%) and HEMA (15wt.%), the degree of conversion varying between 63.4 and 74.5%. The formed copolymers showed high values for water sorption (18.65–57.02μg/mm3) and water solubility (3.51–13.38μg/mm3), and the contact angle was dependent on the presence of CO-DAP (θF1: 66.67°), TMP-DAP (θF2: 55.05°) or AMP-P (θF3: 52.90°) in the photocrosslinked specimens compared to the sample without phosphate monomer (θF4: 82.14°). The scanning electron microscopy image of the dentin–resin composite interface after applying our F1 formulation (pH: 4.1) and its light-curing for 20s supports the evidence of the formation of the hybrid layer with the tooth structure created by self-etching approach, with no gaps or cracks in the adhesive. A comparative analysis of the adhesion achieved with commercial adhesive systems (Single Bond Universal, C-Bond) rather indicates similarities than differences between them. The addition of triclosan methacrylate (1wt.%) into the formulation inhibited the bacterial growth of the Streptococcus mutans and Escherichia coli in the direct contact area due to the covalently linked antibacterial monomer.

Scapholunate ligament injury adversely alters in vivo wrist joint mechanics: An MRI‐based modeling study

We investigated the effects of scapholunate ligament injury on in vivo radiocarpal joint mechanics using image-based surface contact modeling. Magnetic resonance images of 10 injured and contralateral normal wrists were acquired at high resolution (hand relaxed) and during functional grasp. Three-dimensional surface models of the radioscaphoid and radiolunate articulations were constructed from the relaxed images, and image registration between the relaxed and grasp images provided kinematics. The displacement driven models were implemented in contact modeling software. Contact parameters were determined from interpenetration of interacting bodies and a linear contact rule. Peak and mean contact pressures, contact forces and contact areas were compared between the normal and injured wrists. Also measured were effective (direct) contact areas and intercentroid distances from the grasp images. Means of the model contact areas were within 10 mm(2) of the direct contact areas for both articulations. With injury, all contact parameters significantly increased in the radioscaphoid articulation, while only peak contact pressure and contact force significantly increased in the radiolunate articulation. Intercentroid distances also increased significantly with injury. This study provides novel in vivo contact mechanics data from scapholunate ligament injury and confirms detrimental alterations as a result of injury.

Preparation of tungsten disulfide (WS2) soft-coated nano-textured self-lubricating tool and its cutting performance

This paper proposes a new effective dry cutting tool named tungsten disulfide (WS2) soft-coated nano-textured self-lubricating tool which is fabricated by two steps. First, nano-texture is made on the tool–chip interface of rake face of uncoated YS8 (WC + TiC + Co) cemented carbide cutting inserts by femtosecond laser micromachining technology. Second, WS2 soft coating is deposited on the nano-textured tool by medium-frequency magnetron sputtering, multi-arc ion plating and ion beam assisted deposition technique. Dry turning tests on 45# quenched and tempered steel were carried out with three kinds of cutting tools: conventional YS8 tool, nano-textured tool (CFT), and WS2 soft-coated nano-textured self-lubricating tool (CFTWS). Results show that the cutting forces, cutting temperature, the friction coefficient at the tool–chip interface, and the antiadhesive effect of the nano-textured tools were significantly reduced compared with those of the conventional one. The CFTWS tool had the best cutting performance among all the tools tested under the same test conditions. Through cutting force and cutting temperature theoretical analysis and experimental results, four mechanisms responsible were found. The first one is explained as the formation of the WS2 lubricating film with low shear strength at the tool–chip interface, which was released from the surface nano textures and smeared on the rake face, and served as lubricating additive during dry cutting processes to reduce the cutting forces and cutting temperature. The second one is explained by the reduced contact length at the tool–chip interface of the nano-textured tools; the smaller direct contact area between the chip and tool rake face leads to less friction force, which can also contribute to the decrease of cutting forces and cutting temperature. The third one can be explained that because of the excellent lubricity of the WS2 lubricating film, the antiadhesive effect can be significantly improved which can reduce adhesive wear of the cutting tool and prolong the tool life. The fourth one can be explained that the advantage of CFTWS tool in cutting forces and cutting temperature is obvious in relatively high-speed and high-temperature conditions may be because of ultra-low friction coefficient, high temperature resistance, and the high oxidation resistance of WS2 soft coating which is not sensitive to high cutting temperature and high cutting speed can significantly improve the severe dry cutting environment.

Study of dynamic features of highly energetic reactions by DSC and High-Speed Temperature Scanner (HSTS)

ABSTRACTThe dynamic features of Al2O3 - polytetrafluoroethylene (PTFE) and Al - PTFE reactions in non-isothermal conditions are presented. The Differential Scanning Calorimetry (DSC) and High-Speed Temperature Scanner (HSTS) were used to characterize the Al2O3/Al – PTFE reactions at different heating rates. The study shows that the HSTS instrument can give more information about the reaction mechanism and kinetics than the conventional DSC measurements. In this work we show that high heating rates may reveal exothermic reaction between Al2O3 and PTFE that were previously unidentified. The PTFE can potentially remove the oxide layer from aluminum in the initial period of the reaction and increase the direct contact area between oxygen and aluminum, which increases the reaction velocity and improves the energy release abilities of the system.

Dissolution of explosive compounds TNT, RDX, and HMX under continuous flow conditions

2,4,6-trinitrotoluene (TNT), hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), and octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) are common contaminants around active military firing ranges. Dissolution of these compounds is usually the first step prior to their spreading in subsurface environments. Nevertheless, dissolution of individual TNT, RDX, and HMX under continuous flow conditions has not been well investigated. This study applied spectral confocal microscopy to observe and quantify the dissolution of TNT, RDX, and HMX (<100μm crystals) in micromodel channels. Dissolution models were developed to describe the changes of their radii, surface areas, volumes, and specific surface areas as a function of time. Results indicated that a model incorporating a resistance term that accounts for the surface area in direct contact with the channel surfaces (and hence, was not exposed to the flowing water) described the dissolution processes well. The model without the resistance term, however, could not capture the observed data at the late stage of TNT dissolution. The model-fitted mass transfer coefficients were in agreement with the previous reports. The study highlights the importance of including the resistance term in the dissolution model and illustrates the utility of the newly developed spectral imaging method for quantification of mass transfer of TNT, RDX, and HMX.

Fluid pressure induces osteoclast differentiation comparably to titanium particles but through a molecular pathway only partly involving TNFα

In contrast to the well-understood inflammatory pathway driven by TNFα, by which implant-derived particles induce bone resorption, little is known about the process in which loosening is generated as a result of force-induced mechanical stimulus at the bone-implant interface. Specifically, there is no knowledge as to what cells or signaling pathways couple mechanical stimuli to bone resorption in context of loosening. We hypothesized that different stimuli, i.e., fluid flow versus wear particles, act through different cytokine networks for activation and localization of osteoclasts. By using an animal model in which osteoclasts and bone resorption were induced by fluid pressure or particles, we were able to detect distinct differences in osteoclast localization and inflammatory gene expression between fluid pressure and titanium particles. Fluid pressure recruits and activates osteoclasts with bone marrow contact away from the fluid pressure exposure zone, whereas titanium particles recruit and activate osteoclasts in areas in direct contact to particles. Fluid pressure induced weaker expression of the selected inflammatory related genes, although the eventual degree of osteoclast induction was similar in both models. Using TNFαRa (4 mg/kg) (Enbrel) and dexamethasone (2 mg/kg) as specific and more general suppressors of inflammation we showed that the TNFαRa failed to generate statistically impaired osteoclast generation while dexamethasone was much more potent. These results demonstrate that fluid pressure induces osteoclasts at a different localization than titanium particles by a molecular pathway less associated with TNFα and the innate system, which open up for other pathways controlling pressure induced osteoclastogenesis.