Influence Of Shear Forces Research Articles

Dynamic Covalent Boronic-Acid-Functionalized Alginate/PVA Hydrogels for pH and Shear-Responsive Drug Delivery.

Herein, we investigated hydrogels composed of boronic-acid-functionalized alginate and blended with polyvinyl alcohol (PVA) of different molecular weights to control the release of metoclopramide hydrochloride as a function of pH and shear stress. The functionalization of alginate introduced dynamic covalent bonding and pH-responsive properties that can modulate network connectivity. The study investigated the viscoelastic properties of the hydrogels, their drug release profiles, and their responsiveness to changes in pH and shear forces. The results showed that a higher PVA molecular weight and alkaline pH conditions increased hydrogel viscosity and stiffness due to a more stable and interconnected network structure than acidic pH. Metoclopramide release revealed that the hydrogels exhibited pH-responsive drug release behavior. The drug was more readily released under acidic conditions due to the instability of sp2-hybridized boronate ester bonds. The influence of shear forces on the release of metoclopramide was also investigated at shear rates of 1, 10, and 100 s-1, revealing their effect on matrix stiffening. Research shows that AlgBA/PVA hydrogels have unique properties, such as dynamic covalent bonding, that make them sensitive to external mechanical forces. This sensitivity makes them ideal for applications where physiological conditions trigger drug release.

Photostimuli Reach a Selective Intermediate in a Microflow: One‐Shot Transformation from a Supramolecular Co‐Polymer to a Micro‐Disk Structure

AbstractIn supramolecular chemistry, photostimulants are generally combined with a static solution under thermodynamic equilibrium with no time progression. After reaching the thermodynamic state, self‐assembly events contain various species–a mixture of component molecules, intermediate species, and completed assemblies–which light reaches uniformly. In this study, snapshot control of supramolecular polymerization was first combined with pinpoint photoirradiation using a microflow system. Employing the azobenzene derivative trans‐C3NO as a monomer, a snapshot moment of supramolecular polymerization along a microflow channel was selectively irradiated with UV light at 365 nm in a space‐resolved manner, so that the monomers, intermediates (oligomers), or extended supramolecular polymers were selectively exposed to light stimuli. We found that a pinpoint photostimulus to each snapshot moment had a pronounced effect on the kinetic pathway by tuning the timing at which the snapshot moment of cis‐C3NO was generated. Upon irradiation in the upstream region, in the very early stages before initiating polymerization, supramolecular polymerization was suppressed by generating a less reactive cis‐C3NO monomer. However, photoirradiation does not affect the supramolecular polymers in the downstream region because of their stiff nature. Remarkably, when irradiating the middle stream region involving a soft‐natured intermediate species, supramolecular copolymerization occurred through in situ conversion from trans‐ and cis‐C3NO inside the primitive supramolecular polymer. Loose monomer stacking in the primitive aggregate endows it with mechanoresponsiveness. Under the influence of shear force in a Hagen–Poiseuille flow, the resultant supramolecular copolymers containing geometrically different cis‐isomers were rolled up and transformed into a micrometer‐sized disk‐like structure. During the in situ supramolecular copolymerization and transformation to the disk structure, a liquid–liquid interface generated in the laminar flow acted as a template to fix the orientation of the monomers and supramolecular polymers, leading to the uniform disk formation. Furthermore, monomers’ orientation in the aligned supramolecular polymers are fixed on the interface, on which light is always irradiated in an anisotropic manner. This results in both complexity at the molecular level and long‐range structural order such as regular rolling up at the micrometer range over the molecular scale. By incorporating the photostimulus system, microflow extends its potential for supramolecular chemistry.

Different rheological behaviors of reinforced poly(methylvinylsiloxane) by mesoporous and spherical silica microparticles

To elucidate the mechanism underlying the high performance of mesoporous silica aerogel microparticle (SAG) in reinforcing polymers, the hydrodynamic effect and reinforcement effect of SAG microparticle in Poly-methylvinylsiloxane (PMVS) were investigated. For comparison, regular spherical silica particles (SS) with a comparable particle size and smooth surface were also incorporated into the study as a contrasting filler. It was found that SAG tended to form aggregates with high aspect ratio (shape factor f values between 16-20) and highly branched backbone structures (x = 1.95). However, these aggregates are more loosely packed (df = 1.7) and easily break into smaller flocs under the influence of shear forces. The load-bearing mechanism of the spatial network formed by these aggregates as nodes was akin to physical gels controlled by bond-bending forces (BBFs), with a scaling exponent of G*r with φe-φc of ν = 3.84, close to the theoretical value of the BBFs model. In contrast, the SS particles formed more compact aggregates (f value approximately 1.6) in PMVS, with load-bearing characteristics of the spatial network formed by them closer to chemical gels controlled by central forces (CFs). The scaling exponent of G*r with φe-φc for SS/PMVS was found to be ν = 2.15, close to the theoretical value of the CFs model.

Experimental study and simulation analysis of the fracture mechanism in AFRP milling

The finite element model of aramid fiber reinforced polymer (AFRP) was established using the finite element analysis software, and milling simulation analysis was carried out. The influence of cutting speed and tool diameter on cutting force was obtained. Based on the motion law of the milling cutter, a fiber cutting mechanical model was established, and the influence of shear force and transverse pressure on the quality of the fiber section was analyzed. The milling experiment on AFRP specimens was carried out, and the milling appearance and cutting force variation of cutting speeds at 18.850–31.415 m/min and tool diameters of 1 –5 mm were studied. The results show that the diameter of a 5 mm milling cutter has a neater cutting fiber section and fewer burrs than the diameter of a 1 mm milling cutter, but inadequate sharpness can easily cause serious entrance burrs. Due to the influence of the feed motion, the milling tool feeding direction (X direction) is 42.456% higher than the Y direction cutting force, which can easily cause tool fracture. Increasing cutting speed can reduce cutting force to a certain extent and improve cutting quality. Therefore, choosing a large-diameter milling cutter with a large rake angle or relief angle for high-speed cutting can effectively improve the quality of the AFRP milling entrance and section.

Influence of shear force on ex vivo expansion of hematopoietic model cells in a stirred tank bioreactor

To evaluate shear stress influence on ex vivo expansion of hematopoietic cell lineages for clinical application, in this study, human pro-monocytic cell (namely U937 cell line) was selected as a hematopoietic stem cell (HSC) model and cultured in suspension mode at two different agitation rates (50, 100 rpm) in the stirred bioreactor. At the agitation rate of 50 rpm, the cells achieved higher expansion folds (27.4 fold) with minimal morphological changes as well as apoptotic cell death, while at 100 rpm the expansion fold decreased after 5-day of culture in suspension culture in comparison with static culture and reached 24.5 fold at the end of the culture. The results of glucose consumption and lactate production were also in agreement with the data of fold expansion and indicated the preference of culture in the stirred bioreactor when agitated at 50 rpm. This study indicated the stirred bioreactor system with an agitation rate of 50 rpm and surface aeration may be used as a potential dynamic culture system for clinical applications of hematopoietic cell lineage. The current experiments shed data related to the effect of shear stress on human U937 cells, as a hematopoietic cell model, to set a protocol for expansion of HSCs for biomedical applications.

Nanocracks in nature and industry.

Nanocracks in nature and industry.

Effect of shear force on the rotational performance of straight mortise-tenon joints

Straight mortise-tenon joints resist combined shear and bending action, and their rotational performance significantly influences the seismic performance of traditional timber structures in Asian countries. However, current theoretical study on the rotational performance of such joints was based on pure bending action and neglected the influence of shear force. This paper detailed explained the effect of shear force on the load-resisting mechanism of straight mortise-tenon joints. A theoretical analysis method on the moment-rotation relationship of these joints with consideration of shear force was developed and compared to that based on pure bending action. The proposed theoretical method was verified by using experimental results. Parametric study was further conducted, key factor was identified to evaluate the effect of shear force on the rotational performance of joints, and the applicability of theoretical analysis methods with or without consideration of shear force was given. The research indicated that under combined shear and bending, the rotational performance of straight mortise-tenon joints was mainly influenced by the ratio of the net frame span, sn, to the tenon depth dt. With the decreasing of sn/dt, shear force increasingly reduced the rotational stiffness and moment-carrying capacity of the joints. When sn/dt < 10, the influence of shear force should be considered and the moment-rotation curve of the joints should be calculated by using the theoretical analysis method considering shear and bending action. When sn/dt ≥ 10, the influence of shear force can be neglected and the moment-rotation curve of the joints can be calculated only considering bending.

Influence of Fillers on the Viscosity Properties of One-Pack Polyurethane Sealants

The paper investigates the effect of fillers on the viscosity properties of one-pack polyurethane sealants. It is noted that with the introduction of such mineral fillers as Mikarb, Midol, MTD2 chalk and aluminum hydroxide, the dynamic viscosity of the composition increases uniformly, while when filled with chemically precipitated Calofort SV chalk and MT-GShM talc, an abnormally sharp increase in viscosity is observed. Such an increase in viscosity for Calofort SV is explained by a highly developed surface, in contrast to other fillers. Talc is characterized by a plate-like shape of particles, which leads to a complex orientation of talc particles in the composition and shear difficulties.It was found that a sealant filled with chemically precipitated chalk has more than 100 pts. wt.(parts by weight), per 100 pts. wt. of the prepolymer under the influence of shear forces (at a constant shear rate) during the first 10 minutes of exposure, a sharp decrease in viscosity is observed, which is characteristic of thixotropic compositions, reaching a constant value after 5-10 minutes. After 10 minutes, the thixotropy of the sealant is restored. Talc does not impart thixotropic properties to the sealant composition.

Impact of shear forces on variable cross section shaft stiffness

Influence of shear forces is presented in this paper for static analysis of a shaft with variable cross-section. A stiffness matrix method is used to evaluate displacement and reaction forces on the shaft in regard to the slope deflection equations. The Timoshenko beam theory is addressed according to the shear coefficient and the shear correction factor. Bending moments are calculated.

Systematic Approach to Optimize Injection Molding and Microstructural Analysis of Fiber Reinforced Resins for Anisotropic Mechanical Characterization

Fiber reinforced resin materials are increasingly being used in aviation, automotive, mass transportation and healthcare industries. Engineers are keen to explore new design concepts with such materials, since these materials promises to offer high strength to weight ratio, elimination of secondary operations and ease in process ability to form complex shaped parts through injection molding. The mechanical properties of molded parts made from such materials depends on the orientation of the reinforcing fibers. Such orientation occurs in fiber-reinforced plastics, since the fibers in the plastic melt during processing, will orient in different directions under the influence of shear forces that are driven by flow pattern. This paper provides details on systematic and abusive injection molding of test specimens and characterizing anisotropic mechanical data that can be used for fiber orientation predictions in computer aided engineering programs. Systematic molding as compared to abusive molding, identifies optimum molding parameters that reduces part–to-part variation during injection molding, thereby reduces part rejections. It provides optimum part performance during application and the process settings are repeatable and reproducible. The intention of this paper is to share widely such a method to make this process less of a skill or art. The mechanical properties covered here are elastic, shear modulus and poisson ratio. Scanning electron microscopy (SEM) analysis revealed that most of the fibers are aligned in melt flow direction for systematic molded plaques, leading to higher stiffness and strength characteristics as compared to transverse to melt flow.

Effect of Coarse Aggregate Columns on Angle of Friction in Fine Sandy Soil

Abstract: the study adopted samples from Tigris river shoulders ,which has been subjected to such collapses and cracks. After testing and investigation it was found the soil is formed from river deposits , which can be classified as fine sand soil . It is known that many of the collapses that occurs in the sides of rivers are due to the influence of shear forces . A different of diameters coarse aggregates columns and aggregates sizes used in this study are tested by direct shear test.&#x0D; The main objective of this research to increase the coefficient of friction between the soil particles in the test specimen by adding the coarse aggregate columns to the fine sand soil, In this regard the least void ratio was found as a beneficial index that relates with critical state of friction angle independent on soil gradation. The relations between critical state or high friction angles of the mixture with lower void ratio were determined as a function of addition pressure. The relationships could be useful to determination the strength parameters of (sand gravel mixtures).

Determination of the crack initiation stress, elastic modulus and ultimate crack length in TPBT concrete beams based on shear deformation theory

Shear deformation theory was adopted in this research to analyse the crack initiation stress occurred in the three-point bending test (TPBT) on concrete beams. For TPBT concrete beams with different spans, the influence of shear force on the maximum stress and mid-span deflection was analysed. The relationship of the crack initiation stress, the modulus of rupture and splitting tensile strength was also studied. It was found that the crack initiation stress was about 90 percent of the modulus of rupture provided by the ASTM, British and European codes, and it was 1.125 times of the splitting tensile strength. Experimental study on notched concrete beams was also undertaken to validate the analytical results. For notched concrete beams in TPBT, calculations of elastic modulus and ultimate crack length are presented.

Novel Stenotic Microchannels to Study Thrombus Formation in Shear Gradients: Influence of Shear Forces and Human Platelet-Related Factors.

Thrombus formation in hemostasis or thrombotic disease is initiated by the rapid adhesion, activation, and aggregation of circulating platelets in flowing blood. At arterial or pathological shear rates, for example due to vascular stenosis or circulatory support devices, platelets may be exposed to highly pulsatile blood flow, while even under constant flow platelets are exposed to pulsation due to thrombus growth or changes in vessel geometry. The aim of this study is to investigate platelet thrombus formation dynamics within flow conditions consisting of either constant or variable shear. Human platelets in anticoagulated whole blood were exposed ex vivo to collagen type I-coated microchannels subjected to constant shear in straight channels or variable shear gradients using different stenosis geometries (50%, 70%, and 90% by area). Base wall shears between 1800 and 6600 s−1, and peak wall shears of 3700 to 29,000 s−1 within stenoses were investigated, representing arterial-pathological shear conditions. Computational flow-field simulations and stenosis platelet thrombi total volume, average volume, and surface coverage were analysed. Interestingly, shear gradients dramatically changed platelet thrombi formation compared to constant base shear alone. Such shear gradients extended the range of shear at which thrombi were formed, that is, platelets became hyperthrombotic within shear gradients. Furthermore, individual healthy donors displayed quantifiable differences in extent/formation of thrombi within shear gradients, with implications for future development and testing of antiplatelet agents. In conclusion, here, we demonstrate a specific contribution of blood flow shear gradients to thrombus formation, and provide a novel platform for platelet functional testing under shear conditions.

Numerical investigations of bone remodelling around the mouse mandibular molar primordia

The formation of the alveolar bone, which houses the dental primordia, and later the roots of tooth, may serve as a model to approach general questions of alveolar bone formation. In this respect, this study aimed to investigate the potential interactions between the alveolar bone formation and tooth eruption by using finite element (FE) methods, and to figure out whether the expanding tooth systems induce shear stresses that lead to alveolar bone formation. 3D geometric surface models were generated from the 3D histological data of the heads of mice (C57 Bl/6J) ranging from stages embryonic (E) to postnatal (P) stages E15 to P20 using the reconstruction software 3-Matic. Bone, dentin, enamel and dental follicle around the primordia were generated and converted into 3D FE models. Models were imported into the FE software package MSC.Marc/Mentat. As material parameters of embryonic dentine, pulp, enamel, dental follicle, and bony structures basically are unknown, these were varied from 1% to 100% of the corresponding known material parameters for humans and a sensitivity analysis was performed. Surface loads were applied to the outside surface of dental follicle ranging from 0.1 to 5.0N/mm2. The validity of the model was analysed by comparing the activity pattern of the alveolar bone as determined in the histological study with the loading pattern from the numerical analysis. The results show that when varying the surface loads, the distribution of shear stresses remained same, and while varying the material properties of the hard tissues, the location of highest shear stresses remained stable. Comparison of the histologically determined growth regions with the distribution of shear stresses computed in the numerical model showed a very close agreement. The results provide a strong proof to support Blechschmidt’s hypothesis that the bone in general is created under the influence of shear forces.

A Bayesian approach to modelling the impact of hydrodynamic shear stress on biofilm deformation.

We investigate the feasibility of using a surrogate-based method to emulate the deformation and detachment behaviour of a biofilm in response to hydrodynamic shear stress. The influence of shear force, growth rate and viscoelastic parameters on the patterns of growth, structure and resulting shape of microbial biofilms was examined. We develop a statistical modelling approach to this problem, using combination of Bayesian Poisson regression and dynamic linear models for the emulation. We observe that the hydrodynamic shear force affects biofilm deformation in line with some literature. Sensitivity results also showed that the expected number of shear events, shear flow, yield coefficient for heterotrophic bacteria and extracellular polymeric substance (EPS) stiffness per unit EPS mass are the four principal mechanisms governing the bacteria detachment in this study. The sensitivity of the model parameters is temporally dynamic, emphasising the significance of conducting the sensitivity analysis across multiple time points. The surrogate models are shown to perform well, and produced ≈ 480 fold increase in computational efficiency. We conclude that a surrogate-based approach is effective, and resulting biofilm structure is determined primarily by a balance between bacteria growth, viscoelastic parameters and applied shear stress.

Research on Shear Lag Effect of T-shaped Short-leg Shear Wall

Longitudinal displacement of cross section of T-shaped shortlegshear wall was simplified to three parts: shear lag warpingdisplacement, plane section bending displacement and axialdisplacement. Shear lag warping deformation was assumed ascubic parabola distribution along flange, and based on minimumpotential energy principle, differential equations were deduced;with boundary conditions, a calculation theory for shear lageffect was established. With two T-shaped short-leg shear wallmodels, vertical stresses of flanges were obtained by calculationtheory and finite element calculation respectively, and comparisonbetween theoretical analysis results and numerical calculationresults was made. At last, parameter analysis was carriedout, and the influence of shear force, shear span ratio andheight-thickness ratio on shear lag coefficient was obtained.Research shows that numerical calculation results are in goodagreement with theoretical analysis results, and each parameterhas different influence on shear lag coefficient.

Influence of shear forces on the aggregation and sedimentation behavior of cerium dioxide (CeO2) nanoparticles under different hydrochemical conditions

This study contributed to a better understanding of the behavior of nanoparticles (NPs) in dynamic water. First, the aggregation behavior of CeO2 NPs at different pH values in various salt solutions was examined to determine the appropriate hydrochemical conditions for hydrodynamics study. Second, the aggregation behavior of CeO2 NPs under different shear forces was investigated at pH 4 and ionic strength 0 in various salt solutions to find out whether shear forces could influence the stability of the nanoparticles and if yes, how. Also, five-stage sedimentation tests were conducted to understand the influence of shear stress on the vertical distribution of CeO2 NPs in natural waters. The aggregation test showed that the shear force could increase the collision efficiency between NPs during aggregation and cause a relatively large mass of NPs to remain in suspension. Consequently, the nanoparticles had a greater possibility of continued aggregation. The sedimentation test under static conditions indicated that a large mass of NPs (>1000 nm) sink to the bottom layer, leaving only small aggregates dispersed in the upper or middle layer of the solution. However, later sedimentation studies under stirring conditions demonstrated that shear forces can disrupt this stratification phenomenon. These results suggest that shear forces can influence the spatial distribution of NPs in natural waters, which might lead to different toxicities of CeO2 NPs to aquatic organisms distributed in the different water layers. This study contributes to a better understanding of nanomaterial toxicology and provides a way for further research.

Mechanical reliability of solder joints in PCBs assembled in surface mount technology

Purpose – The purpose of this paper is to determine the dependence of mechanical strength of solder joints on printed circuit boards from the soldering process parameters and operating conditions of the electronic device. Design/methodology/approach – The research was performed using the Taguchi method of planning of experiments. Evaluation of the quality of solder joints was made on the basis of microscopic observations, X-ray analysis and measurements of shear force of solder joints. Findings – The carried out research has shown the influence of the individual parameters of the soldering process on the mechanical strength of solder joints and the mechanism of damage of solder joints under the influence of shear force. Originality/value – The authors present results of their research using advanced techniques of experimental design and analysis of results. In this study, original approach was used to simulate the operational conditions of electronic devices including thermal imaging technology.

Controlled molecular reorientation enables strong cellulose fibers regenerated from ionic liquid solutions

Cellulose is difficult to solubilize and undergoes thermal decomposition prior to melting. In recent years ionic liquids have been evaluated as solvents of cellulose. In the regeneration process the non-solvent governs the resulting material's crystallinity. Water adsorbs to amorphous cellulose, acts as plasticizer and lowers the Tg, hence the degree of crystallinity will affect the potential strain induced reorientation. We prepared regenerated cellulose fibers form ionic liquid using different non-solvents. The influence of shear forces upon cellulose chain alignment during extrusion was simulated in silica based upon rheological measurements. The regenerated fibers had different physical, morphological and mechanical properties. Molecular re-orientation in fibers induced by mechanical strain, at humidities above the Tg, resulted in much improved mechanical properties with the Young's modulus reaching 23.4 ± 0.8 GPa and the stress at break 504.6 ± 51.9 MPa, which is comparable to commercially available cellulose fibers.

Influence of shear force on floc properties and residual aluminum in humic acid treatment by nano-Al13

The impacts of various shear forces on floc sizes and structures in humic acid coagulations by polyaluminum chloride (PACl) and nano-Al13 were comparatively studied in this paper. The dynamic floc size was monitored by use of a laser diffraction particle sizing device. The floc structure was evaluated in terms of fractal dimension, analyzed by small-angle laser light scattering (SALLS). The effect of increased shear rate on residual Al of the coagulation effluents was then analyzed on the basis of different floc characteristics generated under various shear conditions. The results showed that floc size decreased with the increasing shear rate for both Al13 and PACl. Besides, floc strength and re-formation ability were also weakened by the enhanced shear force. Al13 resulted in small, strong and better recoverable flocs than PACl and moreover, in the shear range of 100–300 revolution per minute (rpm) (G=40.7–178.3s−1), the characteristics of HA-Al13 flocs displayed smaller scale changes than those of HA-PACl flocs. The results of residual Al measurements proved that with shear increased, the residual Al increased continuously but Al13 presented less sensitivity to the varying shear forces. PACl contributed higher residual Al than Al13 under the same shear condition.