Elongation Force Research Articles

Electrospun amino-functionalized PDMS as a novel SPME sorbent for the speciation of inorganic and organometallic arsenic species

Sol–gel based amine-functionalized SPME fibers (PDMS-weak anion exchanger) were prepared and used for direct mode extraction of dimethylarsinic acid (DMA), monomethylarsonic acid (MMA), and arsenate (As(V)) from aqueous solutions followed by HPLC-ICPMS determination. Two different methods of coating were employed: (i) electrospinning and (ii) dip coating. Electrospinning was used for the first time for preparation of sol–gel based SPME fibers and was found to be superior in terms of extracted amount of arsenicals, coating homogeneity, accessibility of amine groups on the surface, and preparation time for a single fiber. Various parameters such as solution pH, extraction time, agitation speed, extraction temperature, and ionic strength were studied. Optimum extraction conditions were determined as pH of 5.0, extraction time of 30 min, agitation speed of 700 rpm, and extraction temperature of 20 °C. Extraction ability of the novel coating decreased by the addition of NaCl as a consequence of the competition between anionic arsenic species and chloride ions for active sites of the weak anion exchanger. This novel sol–gel coating prepared by electrospinning was found to be promising for SPME applications. Vibrational spectroscopy revealed the alignment of PDMS chains by elongational force under electrospinning process. The chain alignment accordingly orients the pendant amino functional groups perpendicular to the fiber surface, which may develop the free active functional groups available to the medium and lead to the enhancement of the extraction performance. Moreover, the proposed coating strategy through electrospinning might be able to break new ground for various applications in analytical chemistry as well as other disciplines.

Importance of Direct Metal−π Coupling in Electronic Transport Through Conjugated Single-Molecule Junctions

We study the effects of molecular structure on the electronic transport and mechanical stability of single-molecule junctions formed with Au point contacts. Two types of linear conjugated molecular wires are compared: those functionalized with methylsulfide or amine aurophilic groups at (1) both or (2) only one of its phenyl termini. Using scanning tunneling and atomic force microscope break-junction techniques, the conductance of mono- and difunctionalized molecular wires and its dependence on junction elongation and rupture forces were studied. Charge transport through monofunctionalized wires is observed when the molecular bridge is coupled through a S-Au donor-acceptor bond on one end and a relatively weak Au-π interaction on the other end. For monofunctionalized molecular wires, junctions can be mechanically stabilized by installing a second aurophilic group at the meta position that, however, does not in itself contribute to a new conduction pathway. These results reveal the important interplay between electronic coupling through metal-π interactions and quantum mechanical effects introduced by chemical substitution on the conjugated system. This study affords a strategy to deterministically tune the electrical and mechanical properties through molecular wires.

Activation of A1 Domain Adhesiveness in von Willebrand Factor by Elongational Force

Abstract SCI-16Multiple mechanisms may contribute to activation of von Willebrand factor (vWF) adhesiveness by elongational flow at sites of hemostasis, including enhancement of A1 domain exposure within vWF concatamers and conformational change within the A1 domain or its complex with GPIbα. A receptor and ligand in a single molecule (ReaLiSM) containing the A1 domain, a flexible linker, and GPIbα fused in a single polypeptide and suspended between beads using DNA handles was interrogated with a laser trap. Two pathways for unbinding representing flexed and extended states were previously reported, with the flexed, more stable state predominantly at forces above 10 pN. vWD type 2B mutations in the A1 domain selectively stabilize the extended, high affinity state, whereas platelet-type vWD mutations in GPIbα stabilize both states. With ReaLiSM, we can also measure the kinetics and force-dependence of receptor-ligand binding. Remarkably, we also see two on-rates for receptor-ligand binding, with the faster on-rate predominating above 10 pN and the slower on-rate predominating below 10 pN. vWD type 2B mutations in the A1 domain selectively increased the fast on-rate, whereas platelet-type mutations in GPIbα increased both on-rates. Our results support force-dependent conformational change as one of the mechanisms that activates vWF in hemostasis. Disclosures:No relevant conflicts of interest to declare.

Nanocomposites of polyamide 6/residual monomer with organic-modified montmorillonite and their nanofibers produced by electrospinning

Nanocomposites of an organic-modified montmorillonite (MMT) and polyamide 6 (PA6) with a residual monomer were produced by melt mixing in a torque rheometer. By wide angle X-rays diffraction (WAXD), intercalated/exfoliated structures were observed in the PA6/MMT nanocomposites with 3 and 5 wt. (%) of MMT; on the other hand, when 7 wt. (%) of MMT was added, a nanocomposite with exfoliated structures was obtained due to the predominant linking reactions between the residual monomer and the nanoclays organic surfactant. Solutions of these PA6/MMT nanocomposites at 15, 17 and 20 wt. (%) in formic acid were prepared. The 3 and 5 wt. (%) nanocomposites were successfully electrospun; however, electrospinning of the 7 wt. (%) nanocomposite was not possible. WAXD, scanning and transmission electron microscopy results showed that the 3 and 5 wt. (%) nanofibers with average diameter between 80-250 nm had exfoliated structures. These results indicate that the high elongational forces developed during the electrospinning process changed the initial intercalated/exfoliated structure of the nanocomposites to an exfoliated one.

Developing Skin Analogues for a Robotic Octopus

In order to fabricate a biomimetic skin for an octopus inspired robot, a new process was developed based on mechanical properties measured from real octopus skin. Various knitted nylon textiles were tested and the one of 10-denier nylon was chosen as reinforcement. A combination of Ecoflex 0030 and 0010 silicone rubbers was used as matrix of the composite to obtain the right stiffness for the skin-analogue system. The open mould fabrication process developed allows air bubble to escape easily and the artificial skin produced was thin and waterproof. Material properties of the biomimetic skin were characterised using static tensile and instrumented scissors cutting tests. The Young's moduli of the artificial skin are 0.08 MPa and 0.13 MPa in the longitudinal and transverse directions, which are much lower than those of the octopus skin. The strength and fracture toughness of the artificial skin, on the other hand are higher than those of real octopus skins. Conically-shaped skin prototypes to be used to cover the robotic arm unit were manufactured and tested. The biomimetic skin prototype was stiff enough to maintain it conical shape when filled with water. The driving force for elongation was reduced significantly compared with previous prototypes.

Dynamical behavior in hemilarynx experiments with the false vocal folds attached

Previously, changes in vibrational parameters were reported as a function of varying glottal conditions in hemilarynx experiments (Dollinger and Berry, J Acoust Soc Am, 130(4):2440). Now, dynamical changes will be reported with the false vocal folds still attached, and the results will be contrasted with the results of the previous study. For two different larynges in which the false vocal folds remained intact during sustained phonation, vibrational output was statistically analyzed as a function of glottal airflow, adduction forces, and elongation forces. Global parameters were computed, including empirical eigenfunctions, fundamental frequency, subglottal pressure, and sound intensity level. Similarly, local parameters were analysed at individual locations, including displacements, velocities and accelerations. The recordings were obtained using a digital high-speed camera. Increased airflow resulted in significant statistical changes in all parameter values except the empirical eigenfunctions. For inc...

A Role for Metaphase Spindle Elongation Forces in Correction of Merotelic Kinetochore Attachments

During mitosis, equal segregation of chromosomes depends on proper kinetochore-microtubule attachments. Merotelic kinetochore orientation, in which a single kinetochore binds microtubules from both spindle poles [1], is a major cause of chromosome instability [2], which is commonly observed in solid tumors [3, 4]. Using the fission yeast Schizosaccharomyces pombe, we show that a proper force balance between kinesin motors on interpolar spindle microtubules is critical for correcting merotelic attachments. Inhibition of the plus-end-directed spindle elongation motors kinesin-5 (Cut7) and kinesin-6 (Klp9) reduces spindle length, tension at kinetochores, and the frequency of merotelic attachments. In contrast, merotely is increased by deletion of the minus-end-directed kinesin-14 (Klp2) or overexpression of Klp9. Also, Cdk1 regulates spindle elongation forces to promote merotelic correction by phosphorylating and inhibiting Klp9. The role of spindle elongation motors in merotelic correction is conserved, because partial inhibition of the human kinesin-5 homolog Eg5 using the drug monastrol reduces spindle length and lagging chromosome frequency in both normal (RPE-1) and tumor (CaCo-2) cells. These findings reveal unexpected links between spindle forces and correction of merotelic attachments and show that pharmacological manipulation of spindle elongation forces might be used to reduce chromosome instability in cancer cells.

Interfacial microstructure and mechanical properties of Cu/Al clad sheet fabricated by asymmetrical roll bonding and annealing

Abstract The interfacial microstructure and mechanical properties of Cu/Al clad sheet fabricated by asymmetrical roll bonding and annealing were studied by scanning electron microscope equipped with energy dispersive X-ray detector, micro-hardness, tension and peeling test. The stress state of deformation zone was analyzed qualitatively to express the advantage of asymmetrical roll bonding. The results show that the asymmetrical roll bonding with larger mismatch speed ratio causes severe shear plastic deformation of component metals, and provides a good interface for atoms diffusion during annealing. The interfacial microstructure is improved and interfacial layer thickness increases. The roll bonding with larger speed ratio improves the ultimate tensile strength, elongation and peeling force of clad sheet, and reduces the micro-hardness of interfacial zone.

Biology and physics of von Willebrand factor concatamers.

Structural specialisations enable von Willebrand factor (VWF) to assemble during biosynthesis into helical tubules in Weibel-Palade bodies (WPB). Specialisations include a pH-regulated dimeric bouquet formed by the C-terminal half of VWF and helical assembly guided by the N-terminal half that templates inter-dimer disulphide bridges. Orderly assembly and storage of ultra-long concatamers in helical tubules, without crosslinking of neighboring tubules, enables unfurling during secretion without entanglement. Length regulation occurs post-secretion, by hydrodynamic force-regulated unfolding of the VWF A2 domain, and its cleavage by the plasma protease ADAMTS13 (a disintegrin and metalloprotease with a thrombospondin type 1 motif, member 13). VWF is longest at its site of secretion, where its haemostatic function is most important. Moreover, elongational hydrodynamic forces on VWF are strongest just where needed, when bound to the vessel wall, or in elongational flow in the circulation at sites of vessel rupture or vasoconstriction in haemostasis. Elongational forces regulate haemostasis by activating binding of the A1 domain to platelet GPIbα, and over longer time periods, regulate VWF length by unfolding of the A2 domain for cleavage by ADAMTS13. Recent structures of A2 and single molecule measurements of A2 unfolding and cleavage by ADAMTS13 illuminate the mechanisms of VWF length regulation. Single molecule studies on the A1-GPIb receptor-ligand bond demonstrate a specialised flex-bond that enhances resistance to the strong hydrodynamic forces experienced at sites of haemorrhage.

Adsorbing polymers subject to an elongational force: the effect of pulling direction

We investigate partially directed walk models of polymers adsorbed at a surface under the influence of an applied force. The force can be applied at various angles (from perpendicular to parallel to the surface) and the critical force–temperature curves are strongly angle-dependent. We observe some interesting differences between the two- and three-dimensional cases associated with the degeneracy of the ground state in three dimensions.

Structure−Property Correlations in Hybrid Polymer−Nanoparticle Electrospun Fibers and Plasmonic Control over their Dichroic Behavior

Electrospinning constitutes a simple and versatile approach of fabricating polymer heterostructures composed of nanofibers. A preferred alignment of polymer crystallites stems from complex shear elongational forces and generates a strong intrinsic optical anisotropy in typical electrospun fibers of semicrystalline polymers. While it can prove useful for certain devices, this intrinsic anisotropy can be extremely detrimental for other key applications such as high-performance polymer-based lighting and solar-energy harvesting platforms. We report a dramatic reduction in the intrinsic dichroism of electrospun poly(ethylene oxide) fibers resulting from the incorporation of inorganic nanoparticles in the polymer matrix. This effect is shown to originate from a controllable randomization of the orientational ordering of the crystalline domains in the hybrid nanofibers and not merely from a reduction in crystallinity. This improved understanding of the crystalline structure-optical property correlation then leads to a better control over the intrinsic anisotropy of electrospun fibers using localized surface-plasmon enhancement effects around metallic nanoparticles.

Directed walk models of adsorbing semi-flexible polymers subject to an elongational force

We consider several directed path models of semi-flexible polymers. In each model we associate an energy parameter for every pair of adjacent collinear steps, allowing for a model of a polymer with tunable stiffness. We introduce weightings for vertices or edges in a distinguished plane to model the interaction of a semi-flexible polymer with an impenetrable surface. We also investigate the desorption of such a polymer under the influence of an elongational force and study the order of the associated phase transitions. Using a simple low-temperature theory, we approximate and study the ground state behaviour of the models.

Studies on the fold-ability of coated paperboard (I): Influence of latex on fold-ability during creasing/folding coated paperboard

Papers consist more than 50% of the packaging material. Cartons which have been used for high quality hygiene packaging such as confections and cosmetics are made from coated paperboard. Carton-making process consists of printing on coated paperboard, creasing and then folding it. A frequently occurred trouble in a carton-making process is cracking along a creasing rule during creasing by high mechanical pressure. In order to reduce cracking and improve fold-ability of coated paperboard, this study elucidated the factors affecting cracking in a coated layer which absorbs most of elongation force applied on the surface layer of coated paperboard. Coated paperboard produced with latex having low Tg and small particle size showed good printability, flexible coated layer and consequently reduced cracking due to its good film formability. When the coated paperboard was folded in machine direction, the fold-ability was poor because of fiber orientation.

Investigation of Abutment Displacement of a Full Height Integral Bridges in Dense Granule Backfill

Problem statement: In this study, the behavior of abutment wall in full height frame integral abutment bridges was investigated. It was seen that the effect of backfill soil resistance on behavior of abutment wall movement is mostly neglected in previous studies. In this research, the final bridge superstructure displacement under temperature-induced forces was formulated. In addition, according to the final bridge displacement, the earth pressure that acts as a resistant force on the bridge abutment using the new equation from British design manual for roads and bridges, BA 42/96 was used. Besides, in the construction of integral bridges, the deck and girders are mostly encased into abutment wall, which makes these bridge components as fixed elements. This fix connectivity makes the top abutment wall move along with the bridge deck. Moreover, the abutment wall in integral bridges is made of reinforced concrete and thus, it could be assumed as a rigid mass that has a linear deformation behavior. Approach: To implement a new method to calculate the amount of abutment wall movement at different elevations in full height frame abutment integral bridges, considering the parameters such as temperature changes, bridge deck elongation and the backfill soil resistance. First, internal forces of the bridge abutment were formulated. They were all presented as functions of bridge deck final displacement. Second, different methods to calculate the soil lateral pressure were used. Third, the numerical modeling was applied and the corresponding results due to the bridge deck elongation were extracted. Fourth, the results obtained from phases two and three were compared to obtain some conclusion. Results: The results derived in this study, consisted of four data sets. First, the existing forces such as the bridge deck elongation force, the backfill soil resistance etc. were formulated according to the bridge final displacement. Then after, the static principals revealed the amount of deck final elongation. For the second set, different correlations such as British Standard, Massachusetts manual and etc. which had considered the effect of deck final displacement in their formulas were presented and with regard to the first part, the backfill reactions were obtained. For the third set, by combining the results from set one and two, different values for the deck final displacement were derived. For the next step, according to the fix connectivity of the abutment and the bridge deck, the abutment top elevation displacement was set equal to the deck final displacement. For the bottom elevation, because of the rigidity of the wall and the rotational behavior about its foundation, the displacement was set zero. Therefore, by assuming linear deformation behavior of rigid masses, the abutment deformation profile for different elevations was concluded. For the last set, the bridge computer model was built using SAP2000 and the corresponding results were collected. Conclusion: It was seen that, generally, except for some certain cases, all the used correlations in this study were in a close agreement either with each other or with the Finite Element data. British Standard method had the closest results to the finite element data and thus preferably it is recommended while the others not denied.

Application of atomic force microscopy in bacterial research

The atomic force microscope (AFM) has evolved from an imaging device into a multifunctional and powerful toolkit for probing the nanostructures and surface components on the exterior of bacterial cells. Currently, the area of application spans a broad range of interesting fields from materials sciences, in which AFM has been used to deposit patterns of thiol-functionalized molecules onto gold substrates, to biological sciences, in which AFM has been employed to study the undesirable bacterial adhesion to implants and catheters or the essential bacterial adhesion to contaminated soil or aquifers. The unique attribute of AFM is the ability to image bacterial surface features, to measure interaction forces of functionalized probes with these features, and to manipulate these features, for example, by measuring elongation forces under physiological conditions and at high lateral resolution (<1 A). The first imaging studies showed the morphology of various biomolecules followed by rapid progress in visualizing whole bacterial cells. The AFM technique gradually developed into a lab-on-a-tip allowing more quantitative analysis of bacterial samples in aqueous liquids and non-contact modes. Recently, force spectroscopy modes, such as chemical force microscopy, single-cell force spectroscopy, and single-molecule force spectroscopy, have been used to map the spatial arrangement of chemical groups and electrical charges on bacterial surfaces, to measure cell-cell interactions, and to stretch biomolecules. In this review, we present the fascinating options offered by the rapid advances in AFM with emphasizes on bacterial research and provide a background for the exciting research articles to follow.

Emergent morphogenesis: Elastic mechanics of a self-deforming tissue

Multicellular organisms are generated by coordinated cell movements during morphogenesis. Convergent extension is a key tissue movement that organizes mesoderm, ectoderm, and endoderm in vertebrate embryos. The goals of researchers studying convergent extension, and morphogenesis in general, include understanding the molecular pathways that control cell identity, establish fields of cell types, and regulate cell behaviors. Cell identity, the size and boundaries of tissues, and the behaviors exhibited by those cells shape the developing embryo; however, there is a fundamental gap between understanding the molecular pathways that control processes within single cells and understanding how cells work together to assemble multicellular structures. Theoretical and experimental biomechanics of embryonic tissues are increasingly being used to bridge that gap. The efforts to map molecular pathways and the mechanical processes underlying morphogenesis are crucial to understanding: (1) the source of birth defects, (2) the formation of tumors and progression of cancer, and (3) basic principles of tissue engineering. In this paper, we first review the process of tissue convergent extension of the vertebrate axis and then review models used to study the self-organizing movements from a mechanical perspective. We conclude by presenting a relatively simple “wedge-model” that exhibits key emergent properties of convergent extension such as the coupling between tissue stiffness, cell intercalation forces, and tissue elongation forces.

Effect of thrombin and bradykinin on endothelial cell mechanical properties monitored through membrane deformation

The endothelium is closely implicated in the control and maintenance of the vascular homeostasis. The functions of endothelial cells are highly regulated by several agonists of G protein-coupled receptors (GPCR), which can mediate signals involved in morphological remodeling. Here, we evaluated the mechanical properties of human umbilical vein endothelial cells (HUVEC) in responses to two physiological agonists namely thrombin and bradykinin. We used the atomic force microscopy (AFM) technique to study changes in cell membrane stiffness and interaction between the actin cytoskeleton and the cell membrane. HUVEC stimulated with thrombin (10 nM) and bradykinin (1 microM) showed a temporal increase in their membrane stiffness from 5.0 +/- 0.1 kPa (control) to 8.2 +/- 0.4 kPa (thrombin) and 7.3 +/- 0.5 kPa (bradykinin) and in membrane tethers elongation forces from 43.9 +/- 0.9 pN (control) to 49.5 +/- 0.8 pN (thrombin) and 53.1 +/- 0.8 pN (bradykinin). These results were consistent with the reorganization of the actin cytoskeleton observed in fluorescence microscopy. This study demonstrates that these agonists induce important modifications of the cell membrane properties that can be directly linked to the reorganization and the interaction of the actin cytoskeleton near the apical side of the membrane. These changes in the mechanical properties of endothelial cells provide relevant informations in the biological and pathophysiological behaviors of endothelial cells.

Bulk free‐radical polymerization of styrene on a spinning disc reactor

AbstractThe bulk free‐radical polymerization of styrene was carried out on a spinning disc reactor (SDR) with prepolymer feeds previously prepared in a stirred batch reactor at 70°C. The SDR significantly enhanced the reaction rate when the conversion of the prepolymer feed was about 50%. There was an optimal disc rotation speed, that is, 1500 rpm, at which the conversion enhancement was maximized. Increasing the disc rotation speed up to 1500 rpm increased the conversion, but a further increase beyond this speed caused the conversion enhancement to decrease. This behavior could be attributed to the dual effect of the disc speed (controlling both the residence time and the effective radial mixing of the reaction media) on the disc. On the other hand, the multipass disc feeding mode was used as an approach to increase the residence time and evolution of the conversion of the reacting mixture in the SDR. Surprisingly, a maximum conversion change of about 40% was achieved for a prepolymer feed of 50% after three passes across the rotating disc. Furthermore, the effect of multipass disc feeding on the molecular characteristics of the SDR products was investigated. In comparison with the results obtained at a feed conversion of 30%, the weight‐average molecular weight, the z‐average molecular weight, and the polydispersity index of the three‐pass SDR products prepared with a 50% feed conversion at a rotation speed of 1500 rpm were lower than those of the one‐pass products. This behavior could be attributed to probable chain scission of long polymer chains as a result of the high shear and elongation forces that arose on the disc surface. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Mesendoderm cells induce oriented cell division and invagination in the marine shrimp Sicyonia ingentis

The mesendoderm (ME) cells are the two most vegetal blastomeres in the early developing embryo of the marine shrimp Sicyonia ingentis. These two cells enter mitotic arrest for three cycles after the 5th cell cycle (32-cell stage) and ingress into the blastocoel at the 6th cycle (62-cell stage). Circumjacent to the ingressing ME cells are nine presumptive naupliar mesoderm (PNM) cells that exhibit a predictable pattern of spindle orientation into the blastopore, followed by invagination. We examined the role of ME cells and PNM cells in gastrulation using blastomere recombinations and confocal microscopy. Removal of ME progenitors prevented gastrulation. Removal of any other blastomeres, including PNM progenitors, did not interfere with normal invagination. Altered spindle orientations occurred in blastomeres that had direct contact with one of the ME cells; one spindle pole localized to the cytoplasmic region closest to ME cell contact. In recombined embryos, this resulted in an extension of the region of ME-embryo contact. Our results show that ME cells direct the spindle orientations of their adjacent cells and are consistent with a mechanism of oriented cell division being a responsible force for archenteron elongation.

Modelling the adsorption of a polymer subject to an elongational force by directed walk models

We discuss several different directed walk models of a homopolymer adsorbing at a surface when the polymer is subject to an elongational force which hinders the adsorption. These models have the advantage that, within the generating function approach, they can often be solved exactly and that in the stretching regime they give a fair representation of the configurational properties of the polymer. By using combinatorial arguments we analyse how the critical temperature for adsorption depends on the magnitude of the applied force and show that the order of the adsorption transition changes from continuous to first order when a force is applied. We discuss which are the minimal ingredients to add into the model in order to obtain a reentrant phase diagram similar to the one observed in models of DNA mechanical denaturation. Another advantage in using directed walk models is that they can be generalized to study, to some extent, the adsorption transition of random copolymers. Indeed, despite the fact that the quenched model cannot be solved exactly we show that a partial knowledge of the full random problem can be obtained by resorting to an approximation in which the quenched average is approximated by a partial annealing procedure, the so-called Morita approximation.