Local Shear Forces Research Articles

Soft Monolithic Shielded Sensors to Measure Shear and Normal Forces for Local Slip Detection

AbstractSoft force sensors enable closed loop control or autonomous operation of compliant robot systems. A stretchable force sensing surface containing an array of independent sensor units is reported. This design allows for the measurement of local shear and normal forces at multiple locations, independently, providing real‐time, multi‐axis force information at each unit. The sensor array is based on capacitive strain sensing, using liquid metal electrodes and air microchannel for high sensitivity. Electromechanical interference between adjacent sensor units is addressed and eliminated through design optimization and the use of compliant electrical shield layers. A 1D sensor array is applied to gripping tasks, where the independent sensor readings enable detecting local and partial slipping. This study illustrates how the device can be used to explore the dynamics of local forces during the stages of pick up, slip, and release.

Tuneable hydrogel patterns in pillarless microfluidic devices.

Organ-on-chip (OOC) technology has recently emerged as a powerful tool to mimic physiological or pathophysiological conditions through cell culture in microfluidic devices. One of its main goals is bypassing animal testing and encouraging more personalized medicine. The recent incorporation of hydrogels as 3D scaffolds into microfluidic devices has changed biomedical research since they provide a biomimetic extracellular matrix to recreate tissue architectures. However, this technology presents some drawbacks such as the necessity for physical structures as pillars to confine these hydrogels, as well as the difficulty in reaching different shapes and patterns to create convoluted gradients or more realistic biological structures. In addition, pillars can also interfere with the fluid flow, altering the local shear forces and, therefore, modifying the mechanical environment in the OOC model. In this work, we present a methodology based on a plasma surface treatment that allows building cell culture chambers with abutment-free patterns capable of producing precise shear stress distributions. Therefore, pillarless devices with arbitrary geometries are needed to obtain more versatile, reliable, and biomimetic experimental models. Through computational simulation studies, these shear stress changes are demonstrated in different designed and fabricated geometries. To prove the versatility of this new technique, a blood-brain barrier model has been recreated, achieving an uninterrupted endothelial barrier that emulates part of the neurovascular network of the brain. Finally, we developed a new technology that could avoid the limitations mentioned above, allowing the development of biomimetic OOC models with complex and adaptable geometries, with cell-to-cell contact if required, and where fluid flow and shear stress conditions could be controlled.

Bending theory of composite pressure vessels: A closed-form analytical approach

Composite pressure vessels are strategic for the present and future of the aerospace, transportation, and energy industries. These shell structures are utilized to store and transport liquids and gases and are principally composed of a cylindrical shell and two elliptical heads. The current rules for the structural design of composite pressure vessels make use of the membrane theory that excludes the bending of the structure. Nevertheless, the cylindrical shell and the elliptical heads present different curvature radii. These changes generate a localized bending deformation that determines an increase in the stress state as an effect of a local bending moment and shear force distributions that arise in the geometric transition zone. The stresses related to the bending effects die out rapidly, moving away from the junction plane, but they are sensibly higher than the membrane stress and, therefore, cannot be neglected in the mechanical assessment. Here, a closed-form analytical solution for the bending theory of composite shells is proposed. It can assist in the design of composite pressure vessels and drive the design towards reliable configurations for structural integrity. Using the Donnell–Mustari–Vlasov theory for thin-walled composite shells, the governing fourth-order differential equation is deduced and solved to obtain the displacements and stresses acting in the junction. The analytical results are successfully compared with those of reference finite element models for validation; their accuracy is proved considering different thicknesses, lay-ups, and flattening factors of the vessel

Bilateral L5 pedicle fracture with L5-S1 spondylolisthesis after single-level L4-5 posterior lumbar interbody fusion: illustrative case.

Single-level posterior lumbar interbody fusion (PLIF) or transforaminal lumbar interbody fusion (TLIF) is a commonly performed surgical procedure for L4-5 isthmic spondylolisthesis. Postoperative L5 pedicle fracture with rapidly progressive spondylolisthesis at L5-S1 segment after L4-5 PLIF/TLIF is quite rare, and the etiology remains unclear. This report describes this rare complication and proposes a possible etiology focusing on the lumbosacral sagittal imbalance characterized by an anteriorly shifted lumbar loading axis. The authors report a case complicated by L5 bilateral pedicle fractures and rapidly progressive spondylolisthesis at the L5-S1 segment very early after a single-level PLIF for L4-5 isthmic spondylolisthesis. Meyerding grade III anterolisthesis was observed at L5-S1 segment by 3 months after the initial surgery. Additional surgery was performed, and the fixation was extended to L4-ilium. Fracture healing was observed at 6 months postoperatively. This complication may have been caused by abnormal local shear forces on the posterior neural arch of L5 vertebra and L5-S1 intervertebral disc, which were triggered by the fusion surgery for L4 shear-type spondylolisthesis. L4 sagittal vertical axis is considered a reasonable parameter representing lumbosacral sagittal imbalance with an anteriorly shifted loading axis and may be a candidate for the predictive parameters of this rare complication.

Research on the Mechanism of the Passive Reinforcement of Structural Surface Shear Strength by Bolts under Structural Surface Dislocation

In order to study the local deformation of an anchor bolt and the improvement in the shear strength of a structural surface under the misalignment of an anchorage structure surface, FLAC3D software was used to simulate granite, sandstone, and coal specimens with anchorage angles of 90° to analyze the damage of the anchoring agent and the changes in the local axial and shear forces of the anchor bolts with the misalignment of the structural surface. The results show that the anchor bolt near the structural surface had significant local characteristics with the misalignment of the structural surface; that is, the length of the local deformation area of the bolt was approximately equal to the length of the damaged area of the anchoring agent, and the stress on the anchor bolt was in a coupled tensile–shear stress state when the bolt reached the yield state. For the fully grouted bolts, it was this significant local feature that made the shear strength of the structural surface increase rapidly under a small shear displacement so that the structural surface reached a stable state. The improvement in the shear strength of the anchoring structural surface was caused by the misalignment of the structural surface. This is referred to as the passive improvement of the shear strength of the anchoring structural surface, which is the mechanism of the bonding section anchor to control the shear displacement of the structural surface and realize the stability of the rock mass.

The Chevron Effect: Reserve Strength of Existing Chevron Frames

Recently an analysis model has been developed to address the large shear forces (the so-called “chevron effect”) that can develop in the connection regions of chevron-braced frames. These shear forces (and the corresponding moments) are the result of the application of the brace forces at the beam flange, eccentric to the beam centerline. Prior to the presentation of these methods, such forces were not generally considered in design, without apparent incident. Sabelli and Saxey presented an alternative model that determines substantially higher resistance in these connections. Both models resolve the shear and moment within the connection region such that forces outside that region are consistent with those determined using a centerline model. Greater resistance can be determined if the flexural strength of braces and the beam outside the connection region are used to resist a portion of the chevron moment. This paper presents a complete plastic-mechanism strength of the chevron frame with yielding of the beam web due to the local shear forces. This complete plastic mechanism strength can confirm the adequacy of existing designs that did not consider the chevron effect.

Local Shearing Force Measurement during Frictional Sliding Using Fluorogenic Mechanophores.

When two macroscopic objects touch, the real contact typically consists of multiple surface asperities that are deformed under the pressure that holds the objects together. Application of a shear force makes the objects slide along each other, breaking the initial contacts. To investigate how the microscopic shear force at the asperity level evolves during the transition from static to dynamic friction, we apply a fluorogenic mechanophore to visualize and quantify the local interfacial shear force. When a contact is broken, the shear force is released and the molecules return to their dark state, allowing us to dynamically observe the evolution of the shear force at the sliding contacts. We find that the macroscopic coefficient of friction describes the microscopic friction well, and that slip propagates from the edge toward the center of the macroscopic contact area before sliding occurs. This allows for a local understanding of how surfaces start to slide.

Low-intensity pulsed ultrasound/nanomechanical force generators enhance osteogenesis of BMSCs through microfilaments and TRPM7

BackgroundLow-intensity pulsed ultrasound (LIPUS) has been reported to accelerate fracture healing, but the mechanism is unclear and its efficacy needs to be further optimized. Ultrasound in combination with functionalized microbubbles has been shown to induce local shear forces and controllable mechanical stress in cells, amplifying the mechanical effects of LIPUS. Nanoscale lipid bubbles (nanobubbles) have high stability and good biosafety. However, the effect of LIPUS combined with functionalized nanobubbles on osteogenesis has rarely been studied.ResultsIn this study, we report cyclic arginine-glycine-aspartic acid-modified nanobubbles (cRGD-NBs), with a particle size of ~ 500 nm, able to actively target bone marrow mesenchymal stem cells (BMSCs) via integrin receptors. cRGD-NBs can act as nanomechanical force generators on the cell membrane, and further enhance the BMSCs osteogenesis and bone formation promoted by LIPUS. The polymerization of actin microfilaments and the mechanosensitive transient receptor potential melastatin 7 (TRPM7) ion channel play important roles in BMSCs osteogenesis promoted by LIPUS/cRGD-NBs. Moreover, the mutual regulation of TRPM7 and actin microfilaments promote the effect of LIPUS/cRGD-NBs. The extracellular Ca2 + influx, controlled partly by TRPM7, could participated in the effect of LIPUS/cRGD-NBs on BMSCs.ConclusionsThe nanomechanical force generators cRGD-NBs could promote osteogenesis of BMSCs and bone formation induced by LIPUS, through regulation TRPM7, actin cytoskeleton, and intracellular calcium oscillations. This study provides new directions for optimizing the efficacy of LIPUS for fracture healing, and a theoretical basis for the further application and development of LIPUS in clinical practice.

Design for Local Web Shear at Brace Connections: An Adaptation of the Uniform Force Method

Recent literature has examined local shear forces in beams in chevron braced frames (Fortney and Thornton, 2015). Subsequently, design methods based on optimal stress distributions to address these shears were developed (Sabelli and Arber, 2017; Sabelli and Saxey, 2021). This paper extends those design methods to gusset connections at columns, utilizing the adaptability of the Uniform Force Method to facilitate design to reduce required member shear strength. The design model presented reduces the required member shear strength required, as compared to the conventional application of the Uniform Force Method. The model allows for redistribution of force from the beam interface to the column interface using a “bypass method,” as well as utilizing the gusset plate as part of a moment connection using the “haunch method.” Finite element analyses are used to confirm the adequacy of a design employing these methods.

Three-Axis Capacitive Sensor Arrays for Local and Global Shear Force Detection

We report the real time characterization and measurement results of a new tri-axial capacitive sensing array. Each unit cell of the Kapton based sensor has an overlapping electrode geometry that allows for the measurement of normal and shear force magnitudes, and the estimation of the 2D and 3D angle of the shear force. The use of a patterned Ecoflex dielectric layer further improves the shear force response and the tunability of the sensor. A custom readout circuit was developed to selectively read the differential capacitances in the sensor array. The local (unit cell) and global (array) force response of the sensor was characterized using a tilt stage, allowing us to determine both the normal and the shear response at different angles in the range of 0-20N. The results show that the Unit Cell response is uniform in the linear range of 0-10N for normal forces (4.6fF/N for all four differential capacitances) and shows good sensitivity for shear forces (1.4 fF/N difference between the right and left differential capacitances at the minimum) and low cross talk. Similar results were seen when a global force was applied across the sensor array. 2D and 3D models were developed to extrapolate the shear force angle from the capacitance data. We also characterized the flexible patterned dielectric layer to understand the effect of its structural dimensions on the effective relative permittivity and developed an analytical model to easily calculate the effective relative permittivity, which showed excellent correlation with the experimentally obtained results. [2020-0382]

Design for Local Member Shear at Brace and Diagonal-Member Connections: Full-Height and Chevron Gussets

Large local member shear forces develop in beams in chevron-braced frames due to the delivery of brace forces to beam flanges, which are at a distance from the beam centerline (Fortney and Thornton, 2015, 2017; Hadad and Fortney, 2020). Using the “lower bound theorem” (Thornton, 1984), Sabelli and Arber (2017) developed design methods to address this local member shear by optimizing the internal stress distribution and thus maximizing the resistance utilized in design. This paper further develops those design methods for chevron beams and extends them to gusset connections at columns.

Synergistic Effect Based on Enhanced Local Shear Forces in PVDF/TiO2/CNT Ternary Composites

High-performance polymer composites fabricated by the addition of hybrid fillers have been attracting great attention from the industry and researchers due to their synergistic effect and relativel...

Time dependent stress relaxation and recovery in mechanically strained 3D microtissues.

Characterizing the time-dependent mechanical properties of cells is not only necessary to determine how they deform but also to understand how external forces trigger biochemical-signaling cascades to govern their behavior. At present, mechanical properties are largely assessed by applying local shear or compressive forces on single cells grown in isolation on non-physiological 2D surfaces. In comparison, we developed the microfabricated vacuum actuated stretcher to measure tensile loading of 3D multicellular “microtissue” cultures. Using this approach, we here assessed the time-dependent stress relaxation and recovery responses of microtissues and quantified the spatial viscoelastic deformation following step length changes. Unlike previous results, stress relaxation and recovery in microtissues measured over a range of step amplitudes and pharmacological treatments followed an augmented stretched exponential behavior describing a broad distribution of inter-related timescales. Furthermore, despite the variety of experimental conditions, all responses led to a single linear relationship between the residual elastic stress and the degree of stress relaxation, suggesting that these mechanical properties are coupled through interactions between structural elements and the association of cells with their matrix. Finally, although stress relaxation could be quantitatively and spatially linked to recovery, they differed greatly in their dynamics; while stress recovery acted as a linear process, relaxation time constants changed with an inverse power law with the step size. This assessment of microtissues offers insights into how the collective behavior of cells in a 3D collagen matrix generates the dynamic mechanical properties of tissues, which is necessary to understand how cells deform and sense mechanical forces in vivo.

Probing MSC and Tumor Cell Secretome Locally via Dynamic Sampling Platform (DSP)

Background & Aim Within any cell culture, especially on the larger scale of commercial bioreactors, there is considerable heterogeneity that directly impacts the final cell product. This variation results in part from the local shear forces experienced by cells as well as the biochemical microenvironment, e.g., metabolic products and secreted protein factors that can act in a paracrine fashion to modify nearby cells. The ability to measure these critical quality attribute (CQA) biomarkers with high spatial and temporal resolution is foundational to the development of real-time quality monitoring for cell manufacturing. Standard analytical methods quantify neither the local heterogeneity nor the transient nature of cell growth. The Dynamic Sampling Platform (DSP, figure 1) overcomes both barriers by enabling local sampling of the secretome for rapid, high fidelity, and label free CQA identification via inline electrospray ionization mass spectrometry (ESI-MS). Real-time monitoring of the microenvironment with DSP will help predict cell health, viability, and potency, thus enabling the Chemistry, Manufacturing and Controls (CMC) standards for the scale-up and scale-out of cell-based therapies. Methods, Results & Conclusion DSP with ESI-MS sensing enables continuous collection, treatment, and direct infusion of ultra-small samples taken directly from cell culture bioreactors for ESI-MS detection of the cell secretome. DSP-nanoESI-MS is comprised of three elements: 1) a non-invasive sampling interface, which has demonstrated the ability to continuously sample from 2D cell cultures aseptically; 2) a microfabricated mass exchanger for sample treatment which simultaneously removes compounds detrimental to MS analysis, e.g., inorganic salts, and introduces compounds that enhance MS sensitivity; and 3) a spray port for direct infusion nanoESI-MS analysis resulting in identification/fingerprinting of biomolecules in cell cultures. DSP has been applied to multiple live cell cultures to identify differences in the secretome associated with cell state. Analysis of wild type versus interferon gamma primed mesenchymal stromal cells (MSCs) as well as OS-17 and 143-B tumor cell types reveal an enriched ESI-MS signature associated with the different cell types. Localized sampling by DSP is shown to be critical in order to capture higher concentration biomarkers near the cell membrane vs bulk samples that are masked by excessive abundance of biochemical background within the media. The Dynamic Sampling Platform (DSP) samples directly from a cell culture with high spatial resolution to capture critical quality attribute (CQA) biomolecules which indicate the instantaneous cell state and growth trajectory. Rapid, inline sample treatment using the microfabricated mass exchanger removes contaminants, such as inorganic salts, and infuses chemicals that enhance the sensitivity of ESI-MS analysis. Larger CQA biomarkers are selectively retained in the sample channel by the size selective nanomembrane, while smaller contaminants and enhancers transfer across the membrane freely. Real-time electrospray ionization mass spectrometry (ESI-MS) provides detection and identification of broad range of CQA biomolecules with no a priori knowledge of chemical composition.

Residual displacement and residual strain measurement for steel frame under seismic load by integrated dot centroid tracking method

The applicability of the image-based method for residual displacement and strain measurement in a structure which is damaged by seismic load was experimentally investigated. A specimen of steel frame was constructed and was subjected to seismic excitation in one direction. Residual displacement and strain field in a beam-to-column connection which suffered from seismic load was measured by Integrated Dot Centroid Tracking (IDCT) method which is one of the image-based methods. A statistical processing result showed the measurement was achieved with a smaller resolution than residual displacement under a minimum seismic load case. The residual displacement due to local tensile and shear force explained with the deformed triangular mesh which made by the centroids of dots. As a comparison with other measurement methods, an elongation between two centroids of dots on beam and column was compared using a displacement transducer installed inside the beam. The measurement result by the displacement transducer validated compared with a calculated displacement waveform using acceleration. As the number of measurements is increased, both measurement results showed a tendency to increase. Differences of residual displacement by two types measuring method was within 15–20%. The series of experiment in this study revealed the applicability of measurement for real structure using IDCT method.

Skyrmions in anisotropic magnetic fields: strain and defect driven dynamics

ABSTRACTMagnetic skyrmions are particle-like, topologically protected magnetization entities that are promising candidates for information carriers in racetrack-memory schemes. The transport of skyrmions in a shift-register-like fashion is crucial for their embodiment in practical devices. Recently, we demonstrated experimentally that chiral skyrmions in Cu2OSeO3 can be effectively manipulated by a magnetic field gradient, leading to a collective rotation of the skyrmion lattice with well-defined dynamics in a radial field gradient. Here, we employ a skyrmion particle model to numerically study the effects of resultant shear forces on the structure of the skyrmion lattice. We demonstrate that anisotropic peak broadening in experimentally observed diffraction patterns can be attributed to extended linear regions in the magnetic field profile. We show that topological (5-7) defects emerge to protect the six-fold symmetry of the lattice under the application of local shear forces, further enhancing the stability of proposed magnetic field driven devices.

Quasi-1D TiS3 Nanoribbons: Mechanical Exfoliation and Thickness-Dependent Raman Spectroscopy.

Quasi-one-dimensional (quasi-1D) materials enjoy growing interest due to their unusual physical properties and promise for miniature electronic devices. However, the mechanical exfoliation of quasi-1D materials into thin flakes and nanoribbons received considerably less attention from researchers than the exfoliation of conventional layered crystals. In this study, we investigated the micromechanical exfoliation of representative quasi-1D crystals, TiS3 whiskers, and demonstrate that they typically split into narrow nanoribbons with very smooth, straight edges and clear signatures of 1D TiS3 chains. Theoretical calculations show that the energies required for breaking weak interactions between the two-dimensional (2D) layers and between 1D chains within the layers are comparable and, in turn, are considerably lower than those required for breaking the covalent bonds within the chains. We also emulated macroscopic exfoliation experiments on the nanoscale by applying a local shear force to TiS3 crystals in different crystallographic directions using a tip of an atomic force microscopy (AFM) probe. In the AFM experiments, it was possible to slide the 2D TiS3 layers relative to each other as well as to remove selected 1D chains from the layers. We systematically studied the exfoliated TiS3 crystals by Raman spectroscopy and identified the Raman peaks whose spectral positions were most dependent on the crystals' thickness. These results could be used to distinguish between TiS3 crystals with thickness ranging from one to about seven monolayers. The conclusions established in this study for the exfoliated TiS3 crystals can be extended to a variety of transition metal trichalcogenide materials as well as other quasi-1D crystals. The possibility of exfoliation of TiS3 into narrow (few-nm wide) crystals with smooth edges could be important for the future realization of miniature device channels with reduced edge scattering of charge carriers.

Numerical accuracy comparison of two boundary conditions commonly used to approximate shear stress distributions in tissue engineering scaffolds cultured under flow perfusion.

Flow-induced shear stresses have been found to be a stimulatory factor in pre-osteoblastic cells seeded in 3D porous scaffolds and cultured under continuous flow perfusion. However, due to the complex internal structure of the scaffolds, whole scaffold calculations of the local shear forces are computationally intensive. Instead, representative volume elements (RVEs), which are obtained by extracting smaller portions of the scaffold, are commonly used in literature without a numerical accuracy standard. Hence, the goal of this study is to examine how closely the whole scaffold simulations are approximated by the two types of boundary conditions used to enable the RVEs: "wall boundary condition" (WBC) and "periodic boundary condition" (PBC). To that end, lattice Boltzmann method fluid dynamics simulations were used to model the surface shear stresses in 3D scaffold reconstructions, obtained from high-resolution microcomputed tomography images. It was found that despite the RVEs being sufficiently larger than 6 times the scaffold pore size (which is the only accuracy guideline found in literature), the stresses were still significantly under-predicted by both types of boundary conditions: between 20% and 80% average error, depending on the scaffold's porosity. Moreover, it was found that the error grew with higher porosity. This is likely due to the small pores dominating the flow field, and thereby negating the effects of the unrealistic boundary conditions, when the scaffold porosity is small. Finally, it was found that the PBC was always more accurate and computationally efficient than the WBC. Therefore, it is the recommended type of RVE.

Histo-cytochemistry and scanning electron microscopy for studying spatial and temporal extraction of metabolites induced by ultrasound. Towards chain detexturation mechanism

There are more than 1300 articles in scientific literature dealing with positive impacts of Ultrasound-Assisted Extraction (UAE) such as reduction of extraction time, diminution of solvent and energy used, enhancement in yield and even selectivity, intensification of diffusion, and eliminating wastes. This present study aims to understand what are the mechanism(s) behind these positive impacts which will help to design a decision tool for UAE of natural products. Different microscopic observations (Scanning Electron Microscopy (SEM), Environmental Scanning Electron Microscopy (e-SEM), Cyto-histochemistry) have been used for spacial and temporal localization of metabolites in rosemary leaves, which is one of the most studied and most important plant for its antioxidant metabolites used in food industry, during conventional and ultrasound extraction. The study permits to highlight that ultrasound impacted rosemary leaves not by a single or different mechanisms in function of ultrasound power, as described by previous studies, but by a chain detexturation mechanism in a special order: local erosion, shear forces, sonoporation, fragmentation, capillary effect, and detexturation. These detexturation impacts followed a special order during ultrasound treatment leading at the end to the total detexturation of rosemary leaves. These mechanisms and detexturation impacts were identified in glandular trichomes, non-glandular-trichomes and the layer adaxial and abaxial cuticle. Modelling metabolites diffusion phenomenon during conventional and ultrasound extraction with the second Fick’s law allowed the estimation of diffusivities and solvent penetration into the inner tissues and in meantime to accelerate the release of valuable metabolites.

A video imaging method for time-dependent measurements of molecular mass transfer and biofilm dynamics in microchannels

ABSTRACTThe biomass accumulation and movement of biofilms in a microchannel is monitored by optical microscopy. First, the average optical density of the biofilm is monitored in time as a measure of biofilm thickness and structural heterogeneity. These results are used as inputs to calculate changing flow velocities due to resulting excluded volume. Next the displacement velocity of moving biofilm segments was recorded in different places in the microchannel. Quantitative analysis by a particle tracking routine showed differences in displacement velocity near and far from the microchannel corner, which is believed to be related to the local shear forces which vary depending on the height of the biofilm segment and its position in the microchannel. The effect of changing biofilm thickness and different hydrodynamic environments in the microchannel are then discussed in terms of their effects on molecular loading rates. Finally, a demonstration of a flow-templated growth approach as a means to homogenize the growth environment.