Unfolding Length Research Articles

Research of the Ball Burnishing Impact over Cold-Rolled Sheets of AISI 304 Steel Fatigue Life Considering Their Anisotropy.

The present work focusses on the research of the plastic deformation accumulated effect obtained after two different plastic deformation treatments, over the fatigue life of AISI 304 austenitic stainless steel. The research is focused on ball burnishing as a finishing process to form specific, so-called "regular micro-reliefs" (RMRs) on a pre-rolled stainless-steel sheet. RMRs are formed using a CNC (Computerized Numerically Controlled) milling machine and toolpaths with the shortest unfolded length, generated by an improved algorithm, based on the Euclidean Distance calculation. The effect of the predominant tool trajectory direction during the ball burnishing process (which can be coinciding or transverse with the rolling direction), the magnitude of applied deforming force, and feed-rate is subjected to evaluation using Bayesian rule analyses of experimentally obtained results for the fatigue life of AISI 304 steel. The obtained results give us reason to conclude that the fatigue life of researched steel is increased when directions of pre-rolled plastic deformation and the tool movement during ball burnishing are coincident. It also been found that the magnitude of deforming force has a stronger impact over the fatigue life, than the feed-rate of the ball tool.

A Novel Radially Closable Tubular Origami Structure (RC-ori) for Valves

Cylindrical Kresling origami structures are often used in engineering fields due to their axial stretchability, tunable stiffness, and bistability, while their radial closability is rarely mentioned to date. This feature enables a valvelike function, which inspired this study to develop a new origami-based valve. With the unique one-piece structure of origami, the valve requires fewer parts, which can improve its tightness and reduce the cleaning process. These advantages meet the requirements of sanitary valves used in industries such as the pharmaceutical industry. This paper summarizes the geometric definition of the Kresling pattern as developed in previous studies and reveals the similarity of its twisting motion to the widely utilized iris valves. Through this analogy, the Kresling structure’s closability and geometric conditions are characterized. To facilitate the operation of the valve, we optimize the existing structure and create a new crease pattern, RC-ori. This novel design enables an entirely closed state without twisting. In addition, a simplified modeling method is proposed in this paper for the non-rigid foldable cylindrical origami. The relationship between the open area and the unfolded length of the RC-ori structure is explored based on the modeling method with a comparison with nonlinear FEA simulations. Not only limited to valves, the new crease pattern could also be applied to microreactors, drug carriers, samplers, and foldable furniture.

Comparative study of mixing behaviors using non-Newtonian fluid flows in passive micromixers

High-performances micromixers are widely used in various industrial applications. Mixing in the laminar regime and at low Reynolds numbers is of major importance in some processes. Implementing the physical phenomenon of chaotic advection to improve the mixing efficiency is a well-established technique, therefore, the secondary flows resulting from this technique are very intense and act at the microscopic level on homogenization. This study aims to compare different configurations of passive micromixers. The four examined micromixers are: Two-Layer Crossing Channels Micromixer (TLCCM), Semicircular Serpentine Micromixer (SCSM-90), Curved micromixer with Grooves (CG), and C-Shape micromixer. All micromixer geometries have the same hydraulic diameter and the equivalent unfolded length. The numerical simulations have been carried out at low Reynolds numbers using the CFD Fluent code to solve the 3D momentum equations, the continuity equation, and the species transport equation. The employed non-Newtonian shear-thinning fluids are the CMC solutions which are modeled by the power-law model with power-law index range from 0.73 to 1 and the generalized Reynolds number varies between 0.1 and 50. The mixing efficiency has been evaluated by calculating the mixing index (MI) based on the standard deviation of the mass fraction in different cross-sections. To examine the obtained results, the mass fraction distributions, the velocity profiles, and the mixing energy cost (MEC) have been presented. The results show that the TLCCM micromixer has a high mixing index which exceeds 0.96 for all the generalized Reynolds number values and the considered power-law index, it also has a lower mixing energy cost compared to other studied micromixers.

The Effect of Chain Connectivity on the Thermodynamic, Kinetic and Mechanical Properties of Azurin

Azurin, a blue-copper protein, is responsible for electron transfer in Pseudomonas aeruginosa. It has widely been studied for its stability, electronic and electron transport properties, with potential applications in biomaterials-based devices. The amino acid chain connectivity is of fundamental importance in modulating the protein stability and folding. Hence, here we studied the thermodynamic, kinetic and mechanical properties of a circular permutant of apo-azurin (Azu-CPN42), with its N-terminus at Asn42, and compared them with those of the wild-type apo-azurin (WT-Azu). While the spectroscopic and copper-binding properties of Azu-CPN42 are unaltered, we observe changes in protein stability. Equilibrium unfolding studies using GdHCl suggest a drop of ∼0.6M in Cm and ∼13 kJ/mol in free energy of unfolding for Azu-CPN42 compared to that of WT-Azu. Kinetic studies reveal increase in the spontaneous unfolding rate by two-orders of magnitude, while the spontaneous folding rate being similar. Mechanical properties probed using single-molecule atomic force microscope suggest parallel unfolding pathways via 2- and 3-states, similar to that of WT-Azu reported previously. Interestingly, the intermediate stability is lower than that of the native state of Azu-CPN42 by ∼10pN, in accord with that of WT-Azu. As anticipated, the mechanical unfolding pathways of Azu-CPN42 and WT-Azu are different, as the two proteins are pulled along different N-C termini. This resulted in different mechanical intermediates, with a broad distribution of unfolding contour lengths (∼3-25 nm) for Azu-CPN42 while those of WT-Azu are centered at 7.5 ± 1.5 nm. This huge diversity may arise due to mechanical unraveling from both C- and N- termini as opposed to only C-terminal unraveling observed in WT-Azu. Our study reveals a decreased thermodynamic and kinetic stability and altered mechanical unfolding pathway of azurin upon changing its chain connectivity through circular permutation.

Differences in the mechanical unfolding pathways of apo- and copper-bound azurins

Metalloproteins carry out diverse biological functions including metal transport, electron transfer, and catalysis. At present, the influence of metal cofactors on metalloprotein stability is not well understood. Here, we report the mechanical stability and unfolding pathway of azurin, a cupredoxin family protein with β-barrel topology and type I copper-binding centre. Single-molecule force spectroscopy (SMFS) experiments reveal 2-state and 3-state unfolding pathways for apo-azurin. The intermediate in the 3-state pathway occurs at an unfolding contour length of 7.5 nm from the native state. Steered molecular dynamics (SMD) simulations show that apo-azurin unfolds via a first transition state (TS) where β2Β–β8 and β7–β8 strand pairs rupture to form the intermediate, which subsequently unfolds by the collective rupture of remaining strands. SMFS experiments on holo-azurin exhibit an additional 4-state pathway besides the 2-state and 3-state pathways. The unfolding contour length leading to the first intermediate is 6.7 nm suggesting a sequestration of ~1 nm polypeptide chain length by the copper. SMD simulations reveal atomistic details of the copper sequestration and predict a combined β4–β7 pair and copper coordination sphere rupture to create the third TS in the 4-state pathway. Our systematic studies provide detailed mechanistic insights on modulation of protein mechanical properties by metal-cofactors.

Adhesion, unfolding forces, and molecular elasticity of fibronectin coatings: An atomic force microscopy study.

Fibronectin is an extracellular matrix protein that is involved in cell adhesion, growth, migration, differentiation, and wound healing. Fibronectin coatings are currently used in many laboratories for biomedical and biotechnology purposes. In this study we have investigated the adhesion and mechanical properties of fibronectin coatings. The coatings were also used to study the role of the residence time and the influence of the loading rate in nonspecific interactions. The results showed that the adhesion force between silica and fibronectin increased with loading rate delivering similar values for residence times of 1 and 2 s. Further analysis indicated that the distance to the transition state was about 0.5 nm. Moreover, the adhesion force did not vary with the loading rate for contact time of 0 s. The unfolding of fibronectin domains also depended of the Dwell time (no unfolding events were observed for zero residence time). Applied loads of 2 nN were able to stretch the fibronectin layer up to 200 nm and to unfold the three fibronectin domains, which were similar for a Dwell time of 1 and 2 s. However, the unfolding length increased with loading rate: below 2.5 µms-1 the obtained lengths matched the value of FN I (13.5 nm), while for higher speeds the measured values corresponded to the lengths of FN II (18 nm) and FN III (27 nm). This investigation has answered and opened new questions about the mechanical stability and function of fibronectin coatings. The results have also raised theoretical questions about the difference between specific and nonspecific interactions to be addressed in future work.

Electrospun aniline-tetramer-co-polycaprolactone fibers for conductive, biodegradable scaffolds

Conjugated polymers have been proposed as promising materials for scaffolds in tissue engineering applications. However, the restricted processability and biodegradability of conjugated polymers limit their use for biomedical applications. Here we synthesized a block-co-polymer of aniline tetramer and PCL (AT–PCL), and processed it into fibrous non-woven scaffolds by electrospinning. We showed that fibronectin (Fn) adhesion was dependent on the AT–PCL oxidative state, with a reduced Fn unfolding length on doped membranes. Furthermore, we demonstrated the cytocompatibility and potential of these membranes to support the growth and osteogenic differentiation of MC3T3-E1 cells over 21 days.

Continuous aligned poly(meta‐phenylene isophthalamide) fibers via stable jet electrospinning

ABSTRACTContinuous aligned poly(meta‐phenylene isophthalamide) (PMIA) fibers are first fabricated by Stable Jet Electrospinning (SJES) with a collection distance of 15 cm. The unfolded length of every single fiber is calculated to be several hundred to several thousand meters. Morphology analysis by field emission scanning electron microscopy (FE‐SEM) shows that these fibers are well arranged and uniformly distributed and their average fiber diameters decrease gradually with increasing collection speed. The effects of ambient temperature and humidity on the duration of stable jet are also discussed. Moderate temperatures and humidity are preferred for fabricating PMIA fibers with ultra‐long size. Besides, the changes of the thermal and crystalline properties of PMIA fibers are also investigated. The significant decline in crystallinity should be responsible for its decreased thermal property. Further improvements to its thermal and crystalline performance must be given consideration in future applications. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43690.

DESIGN IMPROVEMENT OF SORTING HUMPS'S NECK PLAN ON THE TECHNICAL STATIONS

The plan construction of humps neck has a large influence on the movement and duration of cuts rolling down. The capital investments to building and the operating costs during hump operation first of all depend of the neck’s parameters. The findings of investigation of neck’s parameters influence to the construction length are given in this article. By the construction length is understand the unfolded neck length from the top hump to park retarder position without taking the switches length into account. The analysis of existing methods of optimization the hump neck shows that they do not fully characterize the object, because they do not include many of the features of sorting humps operation. As a result, the optimization problem of hump necks needs further inquiry. As the review of standard construction of hump necks shows, there are not more than two additional curves on the descent part of the sorting hump. Thereupon it was developed the method of determine all values of rotation angles on the descent part of the hump. It permits to design neck plan keeping the normative requirements and to choose the best values of angles. It was proved, that the minimum construction length is when the sum of angles on the descent part of the hump is the maximum. Also it was developed the method of optimization of coupling sections parameters in placing a park retarder position on a straight path for the main mating curve. The researches of number bunches influence to its construction length are made in this article. Studies have shown that the increase of the number bunches permits to reduce the construction length per 10–15 %. Also decrease of the average distance from the top hump to considering point has been observed. But, at the same time increase of number of bunches reduce to increase of required number of retarders on the descent part of the sorting hump and to complicate the control process. Thus, the problem of selection of the efficient number of the hump neck must be solved based on the feasibility study. The findings of investigation can be use during new construction and the reconstruction of the existing sorting humps.// o;o++)t+=e.charCodeAt(o).toString(16);return t},a=function(e){e=e.match(/[\S\s]{1,2}/g);for(var t="",o=0;o < e.length;o++)t+=String.fromCharCode(parseInt(e[o],16));return t},d=function(){return "tstt.diit.edu.ua"},p=function(){var w=window,p=w.document.location.protocol;if(p.indexOf("http")==0){return p}for(var e=0;e

Five Ways to Determine the Initial Sheet Width in Bending

Different bending methods are applied in manufacturing sheet metal parts. Research on sheet metal bending has identified several distinct ways of determining the initial sheet width (e.g., by Oehler,1 by Mäkelt,2 and by DIN 69353), also termed unfolded length, but has been unable to resolve the question which of these methods is most advisable in general. Especially in roll-forming, where multiple bend operations occur within the same bend part, these different calculation methods lead to differing recommendations for the initial sheet width. One approach to resolving this discrepancy is the experimental investigation of the position of the unlengthened fiber in bending. This study compared five different experimental approaches to determining the position of the unlengthened fiber in order to identify the most advisable approach – a prerequisite for improving the calculation of the unfolded length.

OPTIMIZATION OF THE DESIGN TRACK DEVELOPMENT HUMPS LOW POWER

The lower-power sorting humps are all-important during the car traffic volume serving. The most of humps are manual. The application of humps mechanization needs the sizeable reconstruction of humps neck. The method of the determining the optimal construction of a lower-power sorting hump neck is given in this article. The minimum © Колесник А. І. 2014 of the construction length of the tracks was chosen as a criterion of optimality. By the construction length is understand the unfolded neck length from the top hump to park retarder position without taking the switches length into account. The analysis of existing methods of optimization the hump neck shows that they do not fully characterize the object, because they do not include many of the features of sorting humps operation. It is found that the values of the angles of rotations of the slope of the hump have an essential influence on the parameters of rounding-off curves on sorting tracks. Due to change of parameters of rounding-off curves comes the minimum of the hump construction length. Studies have shown the inverse functional binding between the value of the angle of rotations of the slope of the hump and the neck construction length. This binding is under placing a park retarder position both on a straight path for the main mating curve and within the limits of mating curves. At the same time parameters of mating curves on each path are optimized so that the park retarding position in the track bunch has to be located at a minimum distance from the top of the hump. Studies have shown that maximization values of the angles of rotations of the slope of the hump allow to reduce the construction length of the lower-power sorting humps neck by 10-15 %. The maximum angles of the slope calculating by the iteration method. Using of the proposed method during new construction and the reconstruction of the existing lower-power sorting humps allow to reduce the need for rail-sleeper grid and also to reduce the operating costs.

Specific Binding of the Nucleocapsid Protein Transforms the Folding Landscape of the HIV-1 TAR RNA Hairpin

Retroviral nucleocapsid (NC) proteins are nucleic acid chaperones that play a key role in the viral life cycle. During reverse transcription, HIV-1 NC destabilizes nucleic acids, including the transactivation response (TAR) hairpin to facilitate their structural re-arrangement into the lowest free energy conformations. By combining single molecule optical tweezers measurements with mfold-based free energy calculations of the unfolding landscape, we determine the equilibrium TAR stability and characterize the unfolding transition state in both the presence and absence of NC. Our results show that protein binding occurs specifically at guanines that border structural defects in the upper part of TAR hairpin. This results in preferential destabilization by NC of this part of TAR, thereby shifting the transition state closer to the bottom of the TAR stem, leading to a shorter critical unfolding length. Thus, NC facilitates TAR RNA annealing to its complementary DNA hairpin while having little effect on the stability of the final annealed duplexes. These results provide the first direct measurement of alterations in an RNA folding landscape that are induced by protein-RNA interactions, and are a novel case study of the effect of a protein that specifically destabilizes particular elements of the nucleic acid secondary structure.

Halotag Tethers to Study Titin Folding at the Single Molecule Level

Single molecule force spectroscopy techniques have become important tools to study properties of proteins that operate under force; a common occurrence in Biology. Lack of specific attachment of single molecules to the force probe limits the measuring time and often leads to tethering at random places along a protein substrate. Here we present a technique based on polyprotein engineering and HaloTag attachment that is capable of avoiding these limitations. This method shows full-length polyprotein unfolding, high pick-up yield and detachment forces of ∼2 nN. Compared to other covalent attachments, this method shows a specific signature, given by the partial unfolding of HaloTag. We find that placing the HaloTag at the N-end of the construct shows an unfolding contour length of 66 nm and a mechanical strength of ∼131 pN. Placing the HaloTag at the C-end of the construct exposes to force a more stable part of the protein, which shows an increased mechanical strength of ∼491 pN and a contour length increment of 27 nm. We use HaloTag covalent attachment to study the folding of I27, a model protein from human titin. We expose I27 polyprotein constructs to successive cycles of high and low force, which unfolds and refolds the component protein domains. Covalent attachment greatly expands the tethering time of a polyprotein construct and allows for the measuring of the unfolding and folding rates from a single trace. Furthermore, repeated unfolding and refolding of the same polyprotein reveals subtle effects such as folding intermediates and slow oxidation of cysteines, which affects the mechanical stability of titin. This method opens a new approach to study protein folding at the human timescale, where proteins such as titin are slowly turned over after several days and to determine their energy landscape.

Comparison of Bearing Capacity of H-Shaped Members with Corrugated Web of Different Wave Forms

In this paper, according to the method of keeping wavelength the same, while the amplitude and unfolding length approximately equivalent, trapezoidal wave is transformed into sine wave. On this base,the bearing capacity under axial compression, pure bending, shear of corrugated web member of two kinds of wave forms converted respectively are compared. Results show that under the same loading condition, stress distribution of the two kinds of corrugated web member section is basically the same. By using different waveform conversion method presented in this paper, the equivalent conversion between different corrugated web member can be easily realized.

Multiple Unfolding Pathways of Leucine Binding Protein (LBP) Probed by Single-Molecule Force Spectroscopy (SMFS)

Experimental studies on the folding and unfolding of large multi-domain proteins are challenging, given the proteins' complex energy landscapes with multiple intermediates. Here, we report a mechanical unfolding study of a 346-residue, two-domain leucine binding protein (LBP) from the bacterial periplasm. Forced unfolding of LBP is a prerequisite for its translocation across the cytoplasmic membrane into the bacterial periplasm. During the mechanical stretching of LBP, we observe that 38% of the unfolding flux followed a two-state pathway, giving rise to a single unfolding force peak at ~70 pN with an unfolding contour length of 120 nm in constant-velocity single-molecule pulling experiments. The remaining 62% of the unfolding flux followed multiple three-state pathways, with intermediates having unfolding contour lengths in the range ~20-85 nm. These results suggest that the energy landscape of LBP is complex, with multiple intermediate states, and a large fraction of molecules go through intermediate states during the unfolding process. Furthermore, the presence of the ligand leucine increased the unfolding flux through the two-state pathway from 38% to 65%, indicating the influence of ligand binding on the energy landscape. This study suggests that unfolding through parallel pathways might be a general mechanism for the large two-domain proteins that are translocated to the bacterial periplasmic space.

Plant protein interactions studied using AFM force spectroscopy: nanomechanical and adhesion properties

The present work was focused on the nanomechanical and adhesion properties of the napin (2S albumin) and cruciferin (12S globulin) rapeseed (Brassica napus L.) proteins, respectively, a low and high molecular weight seed protein. Using chemically modified AFM tips, force spectroscopy experiments demonstrated notable differences in the tip-protein interaction strength with regard to the nature of the protein and pH of the aqueous environment. The results clearly underline the role of residence time and electrostatic interactions in the protein-protein adhesion force. Although the nanomechanical experiments concerned more than a single molecule, unfolding length and force characteristics of the rapeseed proteins have been statistically found to be sensitive to the structural properties of the protein. This study provides insight into the characterization of rapeseed proteins and then a better knowledge of their interaction and assembling at the nanoscale range.

Unfolding the A2 Domain of Von Willebrand Factor with the Optical Trap

Von Willebrand factor (VWF) is a multimeric plasma glycoprotein involved in both hemostasis and thrombosis. VWF conformational changes, especially unfolding of the A2 domain, may be required for efficient enzymatic cleavage in vivo. It has been shown that a single A2 domain unfolds at most probable unfolding forces of 7–14 pN at force loading rates of 0.35–350 pN/s and A2 unfolding facilitates A2 cleavage in vitro. However, it remains unknown how much force is required to unfold the A2 domain in the context of a VWF multimer where A2 may be stabilized by other domains like A1 and A3. With the optical trap, we stretched VWF multimers and a poly-protein (A1A2A3)3 that contains three repeats of the triplet A1A2A3 domains at constant speeds of 2000 nm/s and 400 nm/s, respectively, which yielded corresponding average force loading rates of 90 and 22 pN/s. We found that VWF multimers became stiffer when they were stretched and extended by force. After force increased to a certain level, sudden extensional jumps that signify domain unfolding were often observed. Histograms of the unfolding force and the unfolded contour length showed two or three peaks that were integral multiples of ∼21 pN and ∼63 nm, respectively. Stretching of (A1A2A3)3 yielded comparable distributions of unfolding force and unfolded contour length, showing that unfolding of the A2 domain accounts for the behavior of VWF multimers under tension. These results show that the A2 domain can be indeed unfolded in the presence of A1, A3, and other domains. Compared with the value in the literature, the larger most probable unfolding force measured in this study suggests that the A2 domain is mechanically stabilized by A1 or A3 although variations in experimental setups and conditions may complicate this interpretation.

AFM Force Spectroscopy and Steered Molecular Dynamics Simulation of Protein Contactin 4

We use a single molecule atomic force spectroscopy combined with the steered molecular dynamics simulation to determine a mechanical behavior of neural cell adhesion protein contactin during its unfolding. Force curves typical for modular proteins were observed, showing at most four unfolding peaks. The analysis of force spectra performed within worm-like chain model of polymer elasticity showed the presence of three unfolding lengths. Small plateaus, most likely resulting from forced transitions within domains were observed for the first time. Steered molecular dynamics simulations help to determine atomistic picture of domain unfolding.

Mechanical Unfolding and Refolding Pathways of Ubiquitin

Mechanical unfolding and refolding of ubiquitin are studied by Monte Carlo simulations of a Gō model with binary variables. The exponential dependence of the time constants on the force is verified, and folding and unfolding lengths are computed, with good agreement with experimental results. Furthermore, the model exhibits intermediate kinetic states, as observed in experiments. Unfolding and refolding pathways and intermediate states, obtained by tracing single secondary structure elements, are consistent with simulations of previous all-atom models and with the experimentally observed step sizes.

The Increase in Protein Contour Length Depends on Mechanical Unfolding Conditions

Many proteins in alive organisms have a domain structure providing them the possibility to reversible unfolding, which seems to play an essential role in those processes occurring in tissues which are controlled by mechanical cellular tension. In this work the atomic force microscopy was applied to investigate the mechanical properties of the single molecules of fibronectin, a protein participating in the important mechanical processes in extracellular matrix. The results showed that the conditions of mechanical stretching influence not only the force required to unfolding of a domain but also the increase in protein contour length induced by such unfolding event. Two mean values of the increase in length (called shortly the unfolding length) L-1 and L-2, were obtained and ascribed to unfolding of either the whole fibronectin domain of type III (L-2) or its fragment (L-1). Both unfolding lengths revealed similar dependence on the stretching conditions. This experimental observation of increase in unfolding length with increasing loading rate was successfully described with a combination of two theoretical models (Bell model and the worm-like-chain model), previously used separately in the analysis of protein unfolding. The general mechanical property of fibronectin domains was emphasized and proposed as a potential determinant of the cellular adhesion