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Force Measurements (force + measurement)
Selected AbstractsA NEW TEST APPARATUS AND METHOD FOR FRICTION FORCE MEASUREMENT IN JOURNAL BEARINGS UNDER DYNAMIC LOADING: Part IEXPERIMENTAL TECHNIQUES, Issue 5 2005A. Biyiklio No abstract is available for this article. [source] Adhesion Characteristics of PDMS Surfaces During Repeated Pull-Off Force Measurements,ADVANCED ENGINEERING MATERIALS, Issue 5 2010Elmar Kroner Abstract To mimic the adhesive effects of gecko toes, artificial surfaces have been manufactured recently using polydimethylsiloxanes (PDMS). However, the effects of repeated contacts on the adhesive properties remain largely unexplored. In this paper we report on the effect of repeated pull-off force measurements on the adhesion behavior of PDMS (polymer kit Sylgard 184, Dow Corning) tested with a borosilicate glass probe. A decrease in pull-off force with increase in number of test cycles is found until a plateau is reached. The initial value and the rate of change in pull-off force strongly depend on the sample preparation procedure, including curing time and cross-linking. It is proposed that the behavior is due to steady coverage of the probe with free oligomers. The results are crucial for developing reusable, durable, and residue-free bioinspired adhesives. [source] Towards Holonomic Control of Janus Particles in Optomagnetic TrapsADVANCED MATERIALS, Issue 47 2009Randall M. Erb A novel "dot" Janus particle is presented, which is compatible with optical traps and magnetic fields, allowing for direct control over five of the particle's degrees of freedom. With an additional constraint of the final sixth degree of freedom, this system represents the highest control ever achieved over freely suspended colloids, opening up the possibility for novel applications in intermolecular force measurement, microfluidics, and self-assembly. [source] Differential activity patterns in the masseter muscle under simulated clenching and grinding forcesJOURNAL OF ORAL REHABILITATION, Issue 8 2005H. J. SCHINDLER summary, The aim of this study was to investigate (i) whether the masseter muscle shows differential activation under experimental conditions which simulate force generation during clenching and grinding activities; and (ii) whether there are (a) preferentially active muscle regions or (b) force directions which show enhanced muscle activation. To answer these questions, the electromyographic (EMG) activity of the right masseter muscle was recorded with five intramuscular electrodes placed in two deep muscle areas and in three surface regions. Intraoral force transfer and force measurement were achieved by a central bearing pin device equipped with three strain gauges (SG). The activity distribution in the muscle was recorded in four different mandibular positions (central, left, right, anterior). In each position, maximum voluntary contraction (MVC) was exerted in vertical, posterior, anterior, medial and lateral directions. The investigated muscle regions showed different amount of EMG activity. The relative intensity of the activation, with respect to other regions, changed depending on the task. In other words, the muscle regions demonstrated heterogeneous changes of the EMG pattern for the various motor tasks. The resultant force vectors demonstrated similar amounts in all horizontal bite directions. Protrusive force directions revealed the highest relative activation of the masseter muscle. The posterior deep muscle region seemed to be the most active compartment during the different motor tasks. The results indicate a heterogeneous activation of the masseter muscle under test conditions simulating force generation during clenching and grinding. Protrusively directed bite forces were accompanied by the highest activation in the muscle, with the posterior deep region as the most active area. [source] Temporal effects of cell adhesion on mechanical characteristics of the single chondrocyteJOURNAL OF ORTHOPAEDIC RESEARCH, Issue 1 2003Wei Huang Abstract Cell adhesion to material surfaces is a fundamental phenomenon in tissue response to implanted devices, and an important consideration in tissue engineering. For example, elucidation of phenomena associated with adhesion of chondrocytes to biomaterials is critical in addressing the difficult problem of articular cartilage regeneration. The first objective of this study was to measure the mechanical adhesiveness characteristics of individual rabbit articular chondrocytes as a function of seeding time to provide further understanding of the cell adhesion process. The second objective was to quantify the force required to separate the plasma membrane from the underlying cytoskeleton as a function of seeding time. After culturing chondrocytes on glass coverslips for 1, 2, 4, 6 h, two biomechanical tests were performed on single chondrocytes: (i) mechanical adhesiveness measurement by the cytodetacher; and (ii) plasma membrane tether formation force measurement by optical tweezers. Cell mechanical adhesiveness increased from 231 ± 149 Pa at 1 h to 1085 ± 211 Pa at 6 h. The cell contact area with the substrata increased from 161 ± 52 ,m2 at 1 h to 369 ± 105 ,m2 at 6 h. The tether formation force increased from 232 ± 23 pN at 1 h to 591 ± 17 pN at 6 h. Moreover, fluorescence staining by rhodamine-phalloidin demonstrated the process of actin spreading within the cytoskeleton from 0.5 to 6 h and allowed for measurement of cell height which was found to decrease from 12.3 ± 2.9 ,m at 0.5 h to 6.2 ± 0.9 ,m at 6 h. © 2002 Orthopaedic Research Society. Published by Elsevier Science Ltd. All rights reserved. [source] INFLUENCE OF MEASUREMENT TECHNIQUE, TEST FOOD, TEETH AND MUSCLE FORCE INTERACTIONS IN MASTICATORY PERFORMANCEJOURNAL OF TEXTURE STUDIES, Issue 1 2007FLÁVIA RIQUETO GAMBARELI ABSTRACT The role of texture and flavors in mastication is evident, but it is difficult to understand the interactions among food properties, oral physiology and perception. Mastication results from rhythmic mandibular movements. The teeth and masticatory muscles together form the mechanism whereby the food particles are fragmented. Masticatory performance and efficiency are defined as the capacity to reduce natural or artificial test materials during mastication, or by counting the number of strokes required to reduce food, respectively. Foods eaten for nourishment are very different from the industrial test materials used to quantify masticatory performance, thus, divergences could arise if the chewable material can or cannot be swallowed. This study presents a synopsis of masticatory performance methods, which is also related to muscle force, number of teeth and test chewing substance diversity. PRACTICAL APPLICATIONS The attributes of food, such as appearance, flavor and texture, as well as its interaction with saliva, number of teeth and conditions of the biomechanical system, influence the chewing process. In addition, reflex control and cognition can influence food perception and breakdown in the mouth. Food acceptability and choice depend on sensory properties of the food, which are perceived during chewing and swallowing. Masticatory performance and maximal occlusal force measurement may provide essential information that could lead to an appropriate diagnosis as regards masticatory function. Masticatory efficiency and performance can be measured to determine the individual's capacity to comminute a natural or a chewable test material. A material with uniform properties that can be reliably reproduced is essential to provide an ideal test bolus for the scientific study of masticatory effectiveness. [source] Contractility of single human dermal myofibroblasts and fibroblastsCYTOSKELETON, Issue 2 2002Louise K. Wrobel Abstract Human dermal myofibroblasts, characterised by the expression of ,-smooth muscle actin, are part of the granulation tissue and implicated in the generation of contractile forces during normal wound healing and pathological contractures. We have compared the contractile properties of single human dermal fibroblasts and human dermal myofibroblasts by culturing them on flexible silicone elastomers. The flexibility of the silicone substratum permits the contractile forces exerted by the cells to be measured [Fray et al., 1998: Tissue Eng. 4:273,283], without changing their expression of ,-smooth muscle actin. The mean contractile force produced by myofibroblasts (2.2 ,N per cell) was not significantly different from that generated by fibroblasts (2.0 ,N per cell) when cultured on a substrata with a low elastomer stiffness. Forces produced by fibroblasts were unaffected by increases in elastomer stiffness, but forces measured for myofibroblasts increased to a mean value of 4.1 ,N/cell. This was associated with a higher proportion of myofibroblasts being able to produce wrinkles on elastomers of high stiffness compared to fibroblasts. We discuss the force measurements at the single cell level, for both fibroblast and myofibroblasts, in relation to the proposed role of myofibroblasts in wound healing and pathological contractures. Cell Motil. Cytoskeleton 52:82,90, 2002. © 2002 Wiley-Liss, Inc. [source] Compensation of actuator delay and dynamics for real-time hybrid structural simulationEARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 1 2008M. Ahmadizadeh Abstract Compensation of delay and dynamic response of servo-hydraulic actuators is critical for stability and accuracy of hybrid experimental and numerical simulations of seismic response of structures. In this study, current procedures for compensation of actuator delay are examined and improved procedures are proposed to minimize experimental errors. The new procedures require little or no a priori information about the behavior of the test specimen or the input excitation. First, a simple approach is introduced for rapid online estimation of system delay and actuator command gain, thus capturing the variability of system response through a simulation. Second, an extrapolation procedure for delay compensation, based on the same kinematics equations used in numerical integration procedures is examined. Simulations using the proposed procedures indicate a reduction in high-frequency noise in force measurements that can minimize the excitation of high-frequency modes. To further verify the effectiveness of the compensation procedures, the artificial energy added to a hybrid simulation as a result of actuator tracking errors is measured and used for demonstrating the improved accuracy in the simulations. Copyright © 2007 John Wiley & Sons, Ltd. [source] Adhesion Characteristics of PDMS Surfaces During Repeated Pull-Off Force Measurements,ADVANCED ENGINEERING MATERIALS, Issue 5 2010Elmar Kroner Abstract To mimic the adhesive effects of gecko toes, artificial surfaces have been manufactured recently using polydimethylsiloxanes (PDMS). However, the effects of repeated contacts on the adhesive properties remain largely unexplored. In this paper we report on the effect of repeated pull-off force measurements on the adhesion behavior of PDMS (polymer kit Sylgard 184, Dow Corning) tested with a borosilicate glass probe. A decrease in pull-off force with increase in number of test cycles is found until a plateau is reached. The initial value and the rate of change in pull-off force strongly depend on the sample preparation procedure, including curing time and cross-linking. It is proposed that the behavior is due to steady coverage of the probe with free oligomers. The results are crucial for developing reusable, durable, and residue-free bioinspired adhesives. [source] INTEGRATED STUDIES ON THE FRESHNESS OF RAINBOW TROUT (ONCORHYNCHUS MYKISS WALBAUM) POSTMORTEM DURING CHILLED AND FROZEN STORAGEJOURNAL OF FOOD BIOCHEMISTRY, Issue 3 2004CARMEL C. WILLS Rainbow trout were killed by two methods, asphyxiation and clubbing. The concentration of ATP in specimens of skeletal muscle taken immediately after death was significantly (P<0.01) higher in clubbed (4.41 ± 0.86 ,mol/g) than in asphyxiated (2.00 ± 0.69 ,mol/g) fish. The shear force (Warner-Bratzler) required to cut the muscle was higher (P<0.05) in clubbed (8.33 ± 0.61 N) than in asphyxiated (6.85 ± 0.98 N) fish. Changes in the concentration of adenine nucleotides and in shear force were measured at intervals during storage at 3C and - 30C. The K value was calculated and was found to be correlated inversely with changes in shear force, Torrymeter readings and sensory assessment. There were no significant differences in the concentrations of ATP and metabolites between muscle sites. There were no differences in shear force measurements between the locations sampled nor between muscle taken from the right and left sides of the fish. [source] Influence of neck rotation and neck lateroflexion on mandibular equilibriumJOURNAL OF ORAL REHABILITATION, Issue 5 2010H. J. SCHINDLER Summary, Neuromuscular interaction between neck and jaw muscles has been reported in several studies. However, the influence of experimentally modified posture of the neck on jaw muscle activity during isometric biting was not investigated so far. The aim of the present study was to test by the aid of simultaneous electromyographic and intraoral bite force measurements whether neck rotation and lateroflexion, in contrast to a straightforward neck position, change the isometric cocontraction patterns of masticatory muscles under identical submaximum bite forces of 50,200 N. Electric muscle activity of all masticatory muscles and changes of the reduction point (RP) of the resultant bite force vectors were examined. An anteroposterior displacement of the RPs could be observed for the rotated and lateroflexed neck position in comparison with the straightforward position. On the other hand, the results revealed no significant differences between bilateral muscle activation under the different test conditions. These findings suggest a force transmission between the neck and the masticatory system, but no essential activity changes in the masticatory muscles under short time posture modification of the neck. [source] Three-dimensional force measurements on oral implants: a methodological studyJOURNAL OF ORAL REHABILITATION, Issue 9 2000J. Duyck This paper describes a methodology that allows in vitro and in vivo quantification and qualification of forces on oral implants. Strain gauges are adapted to the outer surface of 5·5 and 7 mm standard abutments (Brånemark System®, Nobel Biocare, Sweden). The readings of the strain gauges are transformed into a numerical representation of the normal force and the bending moment around the X- and Y- axis. The hardware and the software of the 3D measuring device based on the strain gauge technology is explained and its accuracy and reliability tested. The accuracy level for axial forces and bending moments is 9.72 N and 2.5 N·cm, respectively, based on the current techniques for strain gauged abutments. As an example, an in vivo force analysis was performed in a patient with a full fixed prosthesis in the mandible. Since axial loads of 450 N and bending moments of 70 N·cm were recorded, it was concluded that the accuracy of the device falls well within the scope of our needs. Nevertheless, more in vivo research is needed before well defined conclusions can be drawn and strategies developed to improve the biomechanics of oral implants. [source] A study of sulfamerazine single crystals using atomic force microscopy, transmission light microscopy, and Raman spectroscopyJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 9 2005Xiaoping Cao Abstract Sulfamerazine (SMZ) Form I and II single crystals were prepared from aqueous dispersions of SMZ bulk samples and studied using several microscopic and spectroscopic techniques. Transmission light microscopy and Raman spectroscopy were used to observe and identify single crystals. The results indicated that Form I single crystals tended to be rectangular laths while Form II ones tended to be hexagonal laths. Surface morphology of individual single crystals was further investigated by atomic force microscopy (AFM). AFM images revealed a smooth top surface, a uniform height, and sharp edges for both forms of single crystals. Both height and phase images showed crystalline terraces with different step heights for the top surface of Form I. Surface properties of single crystals were evaluated using AFM force measurements. Experimental results indicated that the top surface of Form I single crystals was more hydrophilic than that of Form II. Theoretical calculations predicted a dominant crystal face of (020) for the Form I single crystals and (002) for the Form II ones. The correlations between calculation predictions and experimental results were discussed. © 2005 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 94:1881,1892, 2005 [source] THE STRUCTURE AND NANOMECHANICAL PROPERTIES OF THE ADHESIVE MUCILAGE THAT MEDIATES DIATOM-SUBSTRATUM ADHESION AND MOTILITY,JOURNAL OF PHYCOLOGY, Issue 6 2003Michael J. Higgins We investigated the adhesive mucilage and mechanism of cell-substratum adhesion of two benthic raphid diatoms, the marine species Craspedostauros australis E. J. Cox and the freshwater species Pinnularia viridis (Nitzsch) Ehrenberg. SEM images of P. viridis and C. australis cells revealed the presence of multistranded tethers that appear to arise along the raphe openings and extend for a considerable distance from the cell before forming a "holdfast-like" attachment with the substratum. We propose that the tethers result from the elongation/stretching of composite adhesive mucilage strands secreted from raphes during the onset of cell adhesion and reorientation. Atomic force microscopy (AFM) force measurements reveal that the adhesive strands originating from the nondriving raphe of live C. australis and P. viridis are highly extensible and accumulate to form tethers. During force measurements tethers can be chemically stained and are seen to extend between the cantilever tip and a cell during elongation and relaxation. In most cases, AFM force measurements recorded an interaction with a number of adhesive strands that are secreted from the raphe. The force curves of C. australis and P. viridis revealed a sawtooth pattern, suggesting the successive unbinding of modular domains when the adhesive strands were placed under stress. In addition, we applied the "fly-fishing" technique that allowed the cantilever, suspended a distance above the cell, to interact with single adhesive strands protruding from the raphe. These force curves revealed sawtooth patterns, although the binding forces recorded were in the range for single molecule interactions. [source] PROBING THE SURFACE OF LIVING DIATOMS WITH ATOMIC FORCE MICROSCOPY: THE NANOSTRUCTURE AND NANOMECHANICAL PROPERTIES OF THE MUCILAGE LAYER,JOURNAL OF PHYCOLOGY, Issue 4 2003Michael J. Higgins Atomic force microscopy (AFM) is used to investigate the topography and material properties of the mucilage layer of live cells of three benthic diatoms, the marine species Crasepdostauros australis E. J. Cox and Nitzschia navis-varingica Lundholm et Moestrup and the freshwater species Pinnularia viridis (Nitzsch) Ehrenberg. Contrary to previous studies, we show that this surface mucilage layer displays unique nanostructural features. In C. australis, tapping mode images revealed a soft mucilage layer encasing the silica cell wall, consisting of a smooth flat surface that was interrupted by regions with groove-like indentations, whereas force measurements revealed the adhesive binding of polymer chains. The elastic responses of these polymer chains, as they were stretched during force measurements, were successfully fitted to the worm-like chain model, indicating the stretching of mostly single macromolecules from which quantitative information was extracted. In P. viridis, tapping mode images of cells revealed a mucilage layer that had the appearance of densely packed spheres, whereas force measurements exhibited no adhesion. In N. navis-varingica, tapping mode images of the outer surface of this cell in the girdle region revealed the absence of a mucilage layer, in contrast to the other two species. In addition to these topographic and adhesion studies, the first quantitative measurement of the elastic properties of microalgal extracellular polymeric substance is presented and reveals significant spatial variation in the C. australis and P. viridis mucilage layers. This study highlights the capacity of AFM in elucidating the topography and mechanical properties of hydrated microalgal extracellular polymeric substance on a nanoscale. [source] Influences of ZnO on the Properties of SrZr0.9Y0.1O2.95 Protonic ConductorJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 5 2008Zhenzhen Peng The effects of ZnO additive on the microstructure, phase formation, and electrical conduction of yttrium-doped strontium zirconate were investigated. The sintering temperature of SrZr0.9Y0.1O2.95 can be lowered to 1350°C by addition of ZnO. The electrical conduction is found to be strongly correlated with the ZnO contents. When the ZnO content is <5 mol%, the electrical conductivity increased with an increase in the ZnO contents. Electromotive force measurements under fuel cell conditions indicated a pure ionic conduction over this range of ZnO contents. However, it had a detrimental effect on the electrical conduction when the ZnO content was more than 6 mol%. The main reason for this is discussed according to the defect chemistry and microstructure. [source] Dispersing Multi-Component and Unstable Powders in Aqueous Media Using Comb-Type Anionic Polymers§JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 6 2006Eric Laarz We have investigated the effect of polymeric dispersants on the rheological properties and consolidation behavior of concentrated cemented carbide (WC,Co) and magnesia (MgO) suspensions. The relatively novel types of comb-type anionic polymers with grafted non-ionic side chains are effective dispersants also in multi-component powder mixtures with a complex solution and surface chemistry and result in more robust suspensions at significantly higher solids loading compared with e.g., a traditional cationic polyelectrolyte. Direct force measurements on comb-type dispersants with different lengths of the grafted ethylene oxide side chains showed that the dispersants adsorb onto a MgO surface and infer a repulsion where the range scales with the length of the poly ethylene oxide side chains. The compressibility and the consolidation behavior of MgO particle networks in response to a centrifugal force field could be related to the estimated thickness of the adsorbed comb-type dispersants. [source] Multifunctional Stretchable Plasma Polymer Modified PDMS Interface for Mechanically Responsive MaterialsPLASMA PROCESSES AND POLYMERS, Issue 1 2010Alexandre Geissler Abstract New stretchable reactive surfaces are developed as platforms for the design of mechanically responsive materials. These surfaces are based on elastic PDMS elastomer substrates. Plasma polymerization leads to the attachment of reactive functionalities on the surface. We show that such functionalised PDMS surfaces exhibit pH-dependent acid-base properties due to the dicarboxylic acid groups. Both contact angle and force measurements highlight the dilution effect of the surface concentration of reactive groups induced by substrate elongation. We show, in particular, that the surfaces can be rendered antifouling by tailoring them with poly(ethylene glycol) (,=,2000) and that the antifouling strength depends upon the elongation of the substrate. [source] Joint And Muscle Forces During ClenchingPROCEEDINGS IN APPLIED MATHEMATICS & MECHANICS, Issue 1 2006Stefan Rues The masticatory system is highly redundant. Therefore, complete knowledge about the activation patterns of the chewing muscles belonging to a specific resultant bite force can only be gained either by simultaneous force- and EMG-measurement or with the help of optimization strategies. In this study, such EMG and force measurements were carried out with 10 test persons and the results compared to those computed with several objective functions. The results show an increase of the joint forces with an increase of the horizontal component of the resultant bite force. The test persons seem to favor energy minimization as control mechanism. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Versatile cloning system for construction of multimeric proteins for use in atomic force microscopyPROTEIN SCIENCE, Issue 9 2002Annette Steward Abstract This manuscript introduces a versatile system for construction of multimeric proteins to be used as substrates for atomic force microscopy. The construction makes use of a cassette system that allows modules to be cut and ligated in any combination in eight different positions. The modules can be sequenced in situ after construction. A three-module fragment can be produced that is of a size amenable to structural and biophysical analysis to check the effect of placing a protein into a multimeric construct. We show that if the parent titin modules are retained in a construct, they can act both as linkers and as an internal standard for the force measurements. Proteins that cannot be expressed solubly in an eight-module homopolymer have been expressed and subject to force measurements using this system. [source] A Model for Cochlear Implant Electrode Insertion and Force Evaluation: Results with a New Electrode Design and Insertion TechniqueTHE LARYNGOSCOPE, Issue 8 2005J Thomas Roland Jr Abstract Objectives and Hypothesis: This study has the specific aim of evaluating the insertion characteristics of a new cochlear implant electrode. Techniques for evaluation of fluoroscopic real time mechanical insertion dynamics, histologic electrode position and trauma results, hydraulic force, and mechanical insertion forces are presented. In addition, this study should serve to present a novel model for cochlear implant electrode insertion evaluations. Study Design: Prospective analysis using a series of analytical techniques. Methods: All studies are conducted in fixed cadaveric temporal bones. Real time fluoroscopic insertion evaluations, histologic evaluations for trauma and electrode position in embedded bones, hydraulic measures, and mechanical intracochlear force measurements are conducted with a current and new electrode. Results: The Contour Advance electrode provides a more reliable and less traumatic insertion when deployed with the Advance Off Stylet technique. This is largely because of a reduction in intracochlear outer wall force generation. Fluoroscopic and histologic analysis reveal a smooth insertion without reliance on cochlear outer wall contact. No hydraulic forces were detected when measured from the superior semicircular canal ampulla. Conclusion: The model used for this study provides valuable information to cochlear implant surgeons and design engineers. The Contour Advance electrode, inserted with the Advance Off Stylet technique, represents an improvement over the Contour electrode inserted with the standard insertion technique. [source] Atomic Force Microscopy as a Tool for Biomedical and Biotechnological Studies,ARTIFICIAL ORGANS, Issue 5 2003Geraldo Antônio Guerrera Cidade Abstract: This work presents different applications in progress with the aid of the atomic force microscopy (AFM) technique for biomedical and biotechnological applications, comprising both the acquisition of three-dimensional images and spectroscopic force measurements, in the following systems: first, low-density lipoprotein (LDL),glycosaminoglycans; second, lectins-polysaccharides; third, mycobacterium leprae cellular wall and Vesicular Stomatites Virus (VSV) with fibronectin laminin, and lipidic membranes; fourth, DNA,complex; and fifth, actin, as well as the development of surface functionalizing protocols and image restoration by means of mathematical techniques. [source] Collar-induced elevation of mRNA and functional activity of 5-HT1B receptor in the rabbit carotid arteryBRITISH JOURNAL OF PHARMACOLOGY, Issue 8 2000Inge S Geerts Hypersensitivity to serotonin (5-HT) develops in rabbit collared carotid arteries. Previous data demonstrated the involvement of 5-HT1 -like receptors which are not active in normal carotid arteries. This study investigated the interaction in the rabbit carotid artery between 5-HT and a moderate tone as this can uncover functional 5-HT1 -like receptors. Furthermore, the expression of messenger RNA (mRNA) and protein of 5-HT1B, 5-HT1D and 5-HT2A receptors was addressed. Silicone collars were placed around the carotid arteries of male New Zealand White rabbits for 1 week. Rings from inside (=collar) and outside (=sham) the collar were either mounted in isolated organ baths for isometric force measurements or frozen in liquid nitrogen to isolate total RNA or proteins which were subsequently analysed by respectively reverse transcriptase-polymerase chain reaction and Western blot analysis. In sham and collared rings concentration-response curves (CRC's) to 5-HT were monophasic. Only in collared segments the presence of a 5-HT2A antagonist (spiperone or ketanserin, 0.1 ,M) revealed a biphasic CRC which was even more pronounced when a moderate tone was induced by KCl pointing to functional 5-HT1 -like receptors. The rabbit carotid artery constitutively expressed 5-HT1B and 5-HT2A mRNA, not 5-HT1D mRNA. Manipulation of the carotid artery increased the 5-HT1B mRNA level. Collar placement raised it even further. The 5-HT2A mRNA level remained unchanged. All the anti-5-HT receptor antibodies tested resulted in variable, non specific patterns with multiple bands. In conclusion, collar placement elevates mRNA expression and activity of the 5-HT1B receptor in the rabbit carotid artery. British Journal of Pharmacology (2000) 131, 1723,1731; doi:10.1038/sj.bjp.0703732 [source] Cyclic Control of the Surface Properties of a Monolayer-Functionalized Electrode by the Electrochemical Generation of Hg NanoclustersCHEMISTRY - A EUROPEAN JOURNAL, Issue 33 2006Michael Riskin Abstract Hg2+ ions are bound to a 1,4-benzenedimethanethiol (BDMT) monolayer assembled on a Au electrode. Electrochemical reduction of the Hg2+,BDMT monolayer to Hg+,BDMT (at E°=0.48 V) and subsequently to Hg0,BDMT (at E°=0.2 V) proceeds with electron-transfer rate constants of 8 and 11 s,1, respectively. The Hg0 atoms cluster into aggregates that exhibit dimensions of 30 nm to 2 ,m, within a time interval of minutes. Electrochemical oxidation of the nanoclusters to Hg+ and further oxidation to Hg2+ ions proceeds with electron-transfer rate constants corresponding to 9 and 43 s,1, respectively, and the redistribution of Hg2+ on the thiolated monolayer occurs within approximately 15 s. The reduction of the Hg2+ ions to the Hg0 nanoclusters and their reverse electrochemical oxidation proceed without the dissolution of mercury species to the electrolyte, implying high affinities of Hg2+, Hg+, and Hg0 to the thiolated monolayer. The electrochemical transformation of the Hg2+ -thiolated monolayer to the Hg0 -nanocluster-functionalized monolayer is characterized by electrochemical means, surface plasmon resonance (SPR), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), atomic force microscopy (AFM), and contact-angle measurements. The Hg0 -nanocluster-modified surface reveals enhanced hydrophobicity (contact angle 76°) as compared to the Hg2+ -thiolated monolayer (contact angle 57°). The hydrophobic properties of the Hg0 -nanocluster-modified electrode are further supported by force measurements employing a hydrophobically modified AFM tip. [source] Combined AFM and Two-Focus SFCS Study of Raft-Exhibiting Model Membranes,CHEMPHYSCHEM, Issue 11 2006Salvatore Chiantia Abstract Dioleoylphosphatidylcholine/sphingomyelin/cholesterol (DOPC/SM/cholesterol) model membranes exhibit liquid,liquid phase separation and therefore provide a physical model for the putative liquid-ordered domains present in cells. Here we present a combination of atomic force microscopy (AFM) imaging, force measurements, confocal fluorescence imaging and two-focus scanning fluorescence correlation spectroscopy (two-focus SFCS) to obtain structural and dynamical information about this model membrane system. Partition coefficients and diffusion coefficients in the different phases were measured with two-focus SFCS for numerous fluorescent lipid analogues and proteins, while being directly related to the lateral organization of the membrane and its mechanical properties probed by AFM. Moreover we show how the combination of these different approaches is effective in reducing artifacts resulting from the use of a single technique. [source] The effect of maximum bite force on marginal bone loss in mandibular overdenture treatment: an in vivo studyCLINICAL ORAL IMPLANTS RESEARCH, Issue 5 2005Frits Van Kampen Abstract: The impact of bite force on the marginal bone response around implants is a subject of debate. This study focused on the effect of maximum bite force on marginal bone levels in mandibular implant overdenture treatment. In addition, the effect of the sequence of 3 different loading conditions on marginal bone loss was evaluated in vivo. The patient population consisted of a group of 18 patients. They received 2 implants in the mandible and a new denture without attachments during the period of submerged implant healing. After second stage surgery, the denture was provided with a ball, magnet or bar-clip attachment. There was a transition of attachment type after 3 and 6 months of function. The sequence in which the attachments were used was randomised. Radiographic marginal bone loss was measured after the period of submerged implant healing and after 3, 6 and 9 months of functional implant loading. Maximum bite force measurements were obtained just prior to second stage surgery with the new denture without attachment. Bite force measurements were also obtained after 3, 6 and 9 months of loading with the implant-retained overdenture. The latter 3 values were averaged. The mean bone loss during the period of submerged healing and during functional loading was 1.7 mm (0.7 mm) and 1.3 mm (0.6 mm), respectively. A relationship between maximum bite force during the period of submerged healing or during the period of functional loading on the one hand and the amount of marginal bone loss on the other could not be demonstrated. The sequence in which the different attachment types were used did not influence the observed amount of marginal bone loss. Résumé L'impact des forces d'occlusion sur la réponse de l'os marginal autour d'implants est sujet à débat. Cette étude s'est centrée sur l'effet de la force d'occlusion maximale sur les niveaux d'os marginaux dans le traitement de prothèses mandibulaires sur implants. De plus l'effet de la séquence de trois conditions de mise en charge différentes sur la perte osseuse marginale a étéévaluée in vivo. Les patients étaient au nombre de douze. Ils avaient reçu deux implants dans la mandibule et une nouvelle prothèse sans attache durant la période de guérison lorsque les implants étaient enfouis. Après la deuxième chirurgie, la prothèse amovible a été utilisée avec une boule, un aimant ou une barre comme attache. Il y avait une transition du type d'attache après trois et six mois de mise en fonction. La séquence suivant laquelle les attaches étaient utilisées était effectuée au hasard. La perte osseuse marginale radiographique a été mesurée après la période de guérison des implants enfouis et après trois, six et neuf mois de mise en fonction. Les mesures de force d'occlusion maximale ont été obtenues juste avant la deuxième chirurgie avec la nouvelle prothèse sans attache. Les mesures de forces d'occlusion ont également été obtenues après trois, six et neuf mois de mise en charge lorsque les implants retenaient la prothèse. Les trois dernières valeurs ont été mélangées. Les pertes osseuses moyennes durant la période de guérison avec les implants enfouis et durant la charge de mise en fonction étaient respectivement de 1,7±0,7 mm et de 1,3±0,6 mm. Une relation entre la force d'occlusion maximale durant la période de guérison avec les implants enfouis ou durant la période de mise en charge fonctionnelle d'une part et la quantité de perte osseuse marginale d'autre part n'a pas pûêtre démontrée. La séquence dans laquelle les différents types d'attache ont été utilisés n'influençaient pas la quantité observée de perte osseuse marginale. Zusammenfassung Der Einfluss der Kaukraft auf die Reaktion des marginalen Knochens um Implantate wir immer wieder diskutiert. Diese Studie konzentrierte sich auf den Einfluss der maximalen Kaukraft auf das marginale Knochenniveau bei Unterkieferimplantaten und Hybridprothesen. Zusätzlich untersuchte man in vivo den Einfluss von drei Phasen mit unterschiedlichen Belastungstypen auf den marginalen Knochenverlust. Es handelte sich um eine Gruppe von 18 Probanden. Alle erhielten zwei Implantate im Unterkiefer und eine neue Prothese, während der submukösen Einheilphase der Implantate noch ohne Retentionselemente. Nach der chirurgischen Freilegung der Implantate fixierte man die Prothesen mit einem Kugelanker, einem Magneten oder einem Steg. Der Wechsel zum nächsten Retentionstyp erfolgte jeweils nach 3 bis 6 Monaten normaler Funktion der Prothesen. Die Abfolge, in welcher man die Retentionselemente einsetzte, wurde zufällig ausgewählt. Den radiologischen marginalen Knochenverlust mass man nach der submukösen Einheilphase der Implantate, sowie nach 3, 6 und 9 Monate einer funktionellen Implantatbelastung. Die maximale Kaukraft wurde genau vor der chirurgischen Freilegung der Implantate mit der neuen Prothese und ohne Attachments gemessen. Zusätzliche Messungen der Kaukraft erfolgten 3, 6 und 9 Monate nach funktioneller Belastung der implantatgetragenen Hybridprothesen. Die letzten drei Werte wurden gemittelt. Der mittlere Knochenverlust während der submukösen Einheilphase betrug 1.7 mm (0.7 mm) und während der funktionellen Belastung 1.3 mm (0.6 mm). Eine Beziehung zwischen der maximalen Kaukraft während der submukösen Einheilung oder während der funktionellen Belastung auf der einen Seite und dem marginalen Knochenverlust auf der anderen Seite konnte nicht gezeigt werden. Die Abfolge, in der die verschiedenen Retentionstypen verwendet wurden, beeinflusste das Ausmass des beobachteten marginalen Knochenverlustes nicht. Resumen El impacto de la fuerza de mordida sobre la respuesta del hueso marginal alrededor de los implantes es motivo de debate. Este estudio está enfocado sobre el efecto de la fuerza de máxima mordida en los niveles de hueso marginal en el tratamiento de sobredentadura mandibular implantosoportada. Además, se evaluó el efecto de la secuencia de 3 condiciones diferentes de carga sobre la pérdida de hueso marginal in vivo. La población de4 pacientes consistió en un grupo de 18 pacientes. Estos recibieron 2 implantes en la mandíbula y una nueva dentadura sin anclajes durante el periodo de cicatrización sumergida de los implantes. Tras la cirugía de segunda fase se suministró una dentadura con anclajes de bola, imanes o barra. Se realizó un cambio en el sistema de anclaje tras 3 y 6 meses en función. La secuencia en la que se emplearon los anclajes fue aleatoria. Se midió la pérdida de hueso marginal radiográfica tras un periodo de cicatrización sumergida y tras 3, 6 y 9 meses de carga funcional de los implantes con la sobredentadura implantosoportada. Los últimos 3 valores se promediaron. La pérdida de hueso media durante el periodo de cicatrización sumergida y durante la carga funcional fue de 1.7 mm (0.7 mm) y 1.3 mm (0.6 mm) respectivamente. No se pudo demostrar una relación entre la fuerza de máxima mordida durante el periodo de cicatrización sumergida o durante el periodo de carga funcional por un lado y la cantidad de pérdida de hueso marginal por otro. La secuencia en la que se emplearon los diferentes tipos de anclajes no influyó en la cantidad de la cantidad de pérdida de hueso marginal observado. [source] | ||||||||||||||||||||||