Strain Mapping Research Articles

Microscale strain concentrations in tissue-engineered osteochondral implants are dictated by local compositional thresholds and architecture

Tissue-engineered osteochondral implants manufactured from condensed mesenchymal stem cell bodies have shown promise for treating focal cartilage defects. Notably, such manufacturing techniques have shown to successfully recapture the bulk mechanical properties of native cartilage. However, the relationships among the architectural features, local composition, and micromechanical environment within tissue-engineered cartilage from cell-based aggregates remain unclear. Understanding such relationships is crucial for identifying critical parameters that can predict in vivo performance. Therefore, this study investigated the relationship among architectural features, composition, and micromechanical behavior of tissue-engineered osteochondral implants. We utilized fast-confocal microscopy combined with a strain mapping technique to analyze the micromechanical behavior under quasi-static loading, as well as Fourier Transform Infrared Spectroscopy to analyze the local compositions. More specifically, we investigated the architectural features and compositional distributions generated from tissue maturation, along with macro- and micro-level strain distributions. Our results showed that under compression, cell-based aggregates underwent deformation followed by body movement, generating high local strain around the boundaries, where local aggrecan concentration was low and local collagen concentration was high. By analyzing the micromechanics and composition at the single aggregate length scale, we identified a strong threshold relationship between local strain and compositions. Namely at the aggrecan concentration below 0.015 arbitrary unit (A.U.) and the collagen concentration above 0.15 A.U., the constructs experienced greater than threefold increase in compressive strain. Overall, this study suggests that local compositional features are the primary driver of the local mechanical environment in tissue-engineered cartilage constructs, providing insight into potential quality control parameters for manufacturing tissue-engineered constructs.

Rejuvenation engineering in metallic glasses by complementary stress and structure modulation

Residual stress engineering is widely used in the design of new advanced lightweight materials. For metallic glasses, attention has been given to structural changes and rejuvenation processes. High-energy scanning X-ray diffraction strain mapping reveals large elastic fluctuations in notched metallic glasses after deformation under triaxial compression. Microindentation hardness mapping hints at a competing hardening–softening mechanism after compression and reveals the complementary effects of stress and structure modulation. Transmission electron microscopy proves that structure modulation and elastic heterogeneity distribution under room temperature deformation are related to shear band formation. Molecular dynamics simulations provide an atomistic understanding of the confined deformation mechanism in notched metallic glasses and the related fluctuations in the elastic and plastic strains. Thus, future focus should be given to stress modulation and elastic heterogeneity, which, together with structure modulation, may allow the design of metallic glasses with enhanced ductility and strain-hardening ability.

Myocardial mechanics and cardiac biomarkers in adults with severe anorexia nervosa.

Anorexia nervosa (AN) is associated with left ventricular (LV) atrophy and unexplained sudden death. Myocardial mechanics have not been well studied in adults with AN. Whether LV mass or illness duration, markers of AN severity, correlate with abnormal strain imaging is unknown. We performed a prospective study among patients hospitalized with severe AN (n = 29) [body mass index (BMI) < 14.5 kg/m2] and sex/age-matched controls (n = 16) (BMI > 18.5 kg/m2). LV ejection fraction (LVEF) was calculated via modified-biplane method and LV mass was derived using the truncated ellipsoid formula. Apical 2-, 3-, and 4-chamber images were used to generate regional strain mapping and global longitudinal strain (GLS). N-terminal brain natriuretic peptide (NT-proBNP) levels were measured and linear regression was used to determine independent predictors of strain. Mean LVEF did not differ (65% ± 6.0 vs. 62% ± 4.4, p = 0.06), but LV mass was substantially reduced (61.6 ± 16.8 vs. 97.6 ± 19.1 g, p < .0001). GLS was similar (-20.6 ± 3.8 vs. -20.9 ± 2.8, p = 0.82), however, the basal strain was worse (-18.7 ± 4.8 vs. -21.9 ± 4.1, p = 0.03). Lower LV mass was associated with worsening GLS (r = -0.40, p = 0.003), but not among controls (p = 0.89). Median (IQR) NT-proBNP (pg/ml) was higher in patients with AN [141 (59-257) vs. 35.5 (21-56.5) p = 0.0007]. Both increasing NT-proBNP and illness duration were associated with worsening strain patterns in AN (both p = .001). While LVEF and GLS did not differ, regional strain variation was noted among patients with AN. Elevated NT-proBNP may reflect increased wall tension from LV atrophy. Whether strain heterogeneity can identify patients with AN, at risk for sudden death, requires further study.

AN OPTIMIZATION FRAMEWORK TO ENABLE THE MEASUREMENT OF STRAIN IN LIGAMENTS USING ULTRASOUND

AbstractObjectivesUltrasound speckle tracking is a safe and non-invasive diagnostic tool to measure soft tissue deformation and strain. In orthopaedics, it could have broad application to measure how injury or surgery affects muscle, tendon or ligament biomechanics. However, its application requires custom tuning of the speckle-tracking algorithm then validation against gold-standard reference data. Implementing an experiment to acquire these data takes months and is expensive, and therefore prohibits use for new applications. Here, we present an alternative optimisation approach that automatically finds suitable machine and algorithmic settings without requiring gold-standard reference data.MethodsThe optimisation routine consisted of two steps. First, convergence of the displacement field was tested to exclude the settings that would not track the underlying tissue motion (e.g. frame rates that were too low). Second, repeatability was maximised through a surrogate optimisation scheme. All settings that could influence the strain calculation were included, ranging from acquisition settings to post-processing smoothing and filtering settings, totalling &gt;1,000,000 combinations of settings. The optimisation criterion minimised the normalised standard deviation between strain maps of repeat measures. The optimisation approach was validated for the medial collateral ligament (MCL) with quasi-static testing on porcine joints (n=3), and dynamic testing on a cadaveric human knee (n=1, female, aged 49). Porcine joints were fully dissected except for the MCL and loaded in a material-testing machine (0 to 3% strain at 0.2 Hz), which was captured using both ultrasound (&gt;14 repeats per specimen) and optical digital image correlation (DIC). For the human cadaveric knee (undissected), 3 repeat ultrasound acquisitions were taken at 18 different anterior/posterior positions over the MCL while the knee was extended/flexed between 0° and 90° in a knee extension rig. Simultaneous optical tracking recorded the position of the ultrasound transducer, knee kinematics and the MCL attachments (which were digitised under direct visualisation post testing). Half of the data collected was used for optimisation of the speckle tracking algorithms for the porcine and human MCLs separately, with the remaining unseen data used as a validation test set.ResultsFor the porcine MCLs, ultrasound strains closely matched DIC strains (R2 &gt; 0.98, RMSE &lt; 0.59%) (Figure 1A). For the human MCL (Figure 1B), ultrasound strains matched the strains estimated from the optically tracked displacements of the MCL attachments. Furthermore, strains developed during flexion were highly correlated with AP position (R = 0.94) with strains decreasing the further posterior the transducer was on the ligament. This is in line with previously reported length change values for the posterior, intermediate and anterior bundles of the MCL.ConclusionsUltrasound speckle tracking algorithms can be adapted for new applications without ground-truth data by using an optimisation approach that verifies displacement field convergence then minimises variance between repeat measurements. This optimisation routine was insensitive to anatomical variation and loading conditions, working for both porcine and human MCLs, and for quasi-static and dynamic loading. This will facilitate research into changes in musculoskeletal tissue motion due to abnormalities or pathologies.Declaration of Interest(a) fully declare any financial or other potential conflict of interest

Examination of NCSL (near-coincidence site lattice) structures formed during β2 (Ni3-xTe2) precipitation in diffusion-bonded PbTe-Ni interfaces – A TEM study

Establishing dependable interconnects within thermoelectric (TE) modules is of utmost significance in ensuring the longevity and functionality of these solid-state devices. PbTe-based devices are used in mid-temperature range applications, with Ni being the most preferred interconnect. The available literature has focused primarily on optimizing the joining parameters. However, fine microstructural features have not been reported that can affect the local semiconducting and mechanical properties. This research paper presents novel findings regarding the formation of previously undiscovered fine (Ni3-xTe2) β2 precipitates resembling Widmanstätten morphology within the PbTe matrix during joining processes. PbTe and Ni discs are diffusion bonded at 600 °C for various holding times. The precipitation is studied through advanced analytical TEM/STEM techniques. The current study leads to two noteworthy observations: 1) specific orientation relationships were discovered between the two phases: [001] PbTe ‖ [001] β2, (020) PbTe ‖ (210) β2 and growth directions were along 〈100〉 in PbTe matrix phase. 2) Formation of near-coincidence site lattice (NCSL) structures occurring periodically at the growing fronts of these precipitates. Atomic scale lattice strain mapping indicates a cyclic state of compression and tension at these interfaces. These findings shed light on local composition changes and strain fields within the PbTe matrix during fine β2 precipitation, which has the potential to impact interface reliability.

Exploiting Mechanics-Based Priors for Lateral Displacement Estimation in Ultrasound Elastography.

Tracking the displacement between the pre- and post-deformed radio-frequency (RF) frames is a pivotal step of ultrasound elastography, which depicts tissue mechanical properties to identify pathologies. Due to ultrasound's poor ability to capture information pertaining to the lateral direction, the existing displacement estimation techniques fail to generate an accurate lateral displacement or strain map. The attempts made in the literature to mitigate this well-known issue suffer from one of the following limitations: 1) Sampling size is substantially increased, rendering the method computationally and memory expensive. 2) The lateral displacement estimation entirely depends on the axial one, ignoring data fidelity and creating large errors. This paper proposes exploiting the effective Poisson's ratio (EPR)-based mechanical correspondence between the axial and lateral strains along with the RF data fidelity and displacement continuity to improve the lateral displacement and strain estimation accuracies. We call our techniques MechSOUL (Mechanically-constrained Second-Order Ultrasound eLastography) and L1 -MechSOUL ( L1 -norm-based MechSOUL), which optimize L2 - and L1 -norm-based penalty functions, respectively. Extensive validation experiments with simulated, phantom, and in vivo datasets demonstrate that MechSOUL and L1 -MechSOUL's lateral strain and EPR estimation abilities are substantially superior to those of the recently-published elastography techniques. We have published the MATLAB codes of MechSOUL and L1 -MechSOUL at https://code.sonography.ai.

Orientation-dependent extreme shear strain in single-crystalline silicon - from elasticity to fracture

Measuring strain accurately at small length scales poses a significant challenge, making it difficult to obtain precise elastic properties of small materials. This becomes particularly pronounced for test geometries beyond micro-pillars and for materials with high elastic limits and high Peierls stresses. This study investigates the elastic strain limits and strain distribution in micro double shear tests conducted on single-crystalline silicon with different crystallographic orientations. In situ scanning electron microscopy images were used to obtain full-field strain maps using digital image correlation. This local strain analysis approach revealed that the shear zones of the test geometry are not solely under pure shear conditions, but also experience superimposed bending. The local strain analysis approach increases the precision of measured elastic properties to ±15% of the literature value compared to deviations of 75-80% using the traditional global strain analysis approach. This study highlights the limitations of the global strain analysis approach in complex specimen geometries and demonstrates the effectiveness of digital image correlation in accurately determining elastic strain at the small length scale. Furthermore, both the low defect density in the samples as well as the small length scales allow for the exploration of orientation dependent strength levels close to the theoretical limit.

Fine-Tuning a Deconvolution Algorithm to Restore Displacement and Strain Maps Obtained with LSA

Fine-Tuning a Deconvolution Algorithm to Restore Displacement and Strain Maps Obtained with LSA

Imaging Light-Induced Migration of Dislocations in Halide Perovskites with 3D Nanoscale Strain Mapping.

In recent years, halide perovskite materials have been used to make high-performance solar cells and light-emitting devices. However, material defects still limit device performance and stability. Here, synchrotron-based Bragg coherent diffraction imaging is used to visualize nanoscale strain fields, such as those local to defects, in halide perovskite microcrystals. Significant strain heterogeneity within MAPbBr3 (MA = CH3 NH3 + ) crystals is foundin spite of their high optoelectronic quality, and both 〈100〉 and 〈110〉 edge dislocations are identified through analysis of their local strain fields. By imaging these defects and strain fields in situ under continuous illumination, dramatic light-induced dislocation migration across hundreds of nanometers is uncovered. Further, by selectively studying crystals that are damaged by the X-ray beam, large dislocation densities and increased nanoscale strains are correlated with material degradation and substantially altered optoelectronic properties assessed using photoluminescence microscopy measurements. These results demonstrate the dynamic nature of extended defects and strain in halide perovskites, which will have important consequences for device performance and operational stability.

A novel machine learning-based approach for nonlinear analysis and in-situ assessment of masonry

Predicting the local and global mechanical response of masonry structures or estimating their in-situ properties are critical and challenging for the design or assessment of these structures. This article presents a fast prediction/assessment model, developed using a conditional generative adversarial neural network (cGAN) to address this challenge. For the first time, the model shows to be capable of establishing a relationship between masonry microstructural features and full-field local/global mechanical response, and vice-versa, overpassing the path dependency of the non-linear mechanical problems. The strain maps and reaction forces of masonry panels are predicted at any load level from images of masonry panels, which embedded information regarding the materials properties and loading scenarios only in colours, without having any prior knowledge of the material properties and constitutive laws and without the need to access these fields in previous loading levels. Also, it is shown that the mechanical properties of masonry constituents can be predicted from full-field strain maps and loading scenarios using the developed model. This promises to become a revolutionary metamodel for the expensive finite element simulations of masonry or to support in-situ/laboratory experimental testing in the identification of masonry material properties.

Comparative proteomics reveals the antibiotic resistance and virulence of Cronobacter isolated from powdered infant formula and its processing environment

Cronobacter species are opportunistic foodborne pathogens that can cause neonatal meningitis, sepsis, and necrotizing enterocolitis. In this genus, certain level strains have high mortality to infant (Cronobacter sakazakii and Cronobacter malonaticus) and antibiotic tolerance. Cronobacter has strong environmental tolerance (acid resistance, high temperature resistance, UV resistance, antibiotic resistance, etc.) and can survive in a variety of environments. It has been isolated in various production environments and products in several countries. However, the relationships between Cronobacter antibiotic tolerance and virulence remain unclear, especially at the molecular level. In this study, 96 strains of Cronobacter were isolated from powdered infant formula and its processing environment and screened for antibiotic tolerance, and proteomic maps of the representative strains of Cronobacter with antibiotic tolerance were generated by analyzing proteomics data using multiple techniques to identify protein that are implicated in Cronobacter virulence and antibiotic resistance. The increase in antibiotic tolerance of Cronobacter had a certain increase in the production of enterotoxin and hemolysin. Only triple tolerated Cronobacter sakazakii decreased the utilization of sialic acid. A total of 16,131 intracellular proteins were detected in eight representative strains, and different proteomes were present in strains with different antibiotic tolerance, including 56 virulence-related proteins. Multiple virulence proteins regulated by unknown genes were also found in the eight isolated representative strains.

Coupled effect of SOC and SOH on tensile behaviors of lithium-ion battery electrodes

The mechanical properties of the electrodes, such as failure stress and failure strain, are critical to the electrochemical properties as well as the internal short-circuit modes of lithium-ion batteries (LIBs). These properties can be altered by different states of charge (SOC) and state of health (SOH). However, there is a lack of understanding of the coupled effect of SOC and SOH on mechanical properties of electrodes. To address this, uniaxial tensile tests combined with microstructure observation are conducted to investigate the effects of SOC, SOH, and strain rate on the mechanical properties. The results show that the effects of SOC and SOH on the anode are non-monotonic, while the failure stress of the cathode decreases slightly with increasing SOC and SOH. Two competing mechanisms (Li+ intercalation and cycle aging) are proposed to explain the non-monotonic response of anode. Additionally, the coupled effect of SOC and strain rate of anode is also discussed. Finally, the yield stress and failure strain maps of electrodes with various SOC and SOH are drawn to enrich the material basic database. The work provides valuable insights into the evolution of mechanical response of electrodes in different electrochemical states.

Seismic Performance of Ordinary and Damage-tolerant Concrete Beam-column Joints under Reversed Cyclic Loading

The adoption of the capacity design principle in modern codes of practice allows for multi-storey frame structures to exhibit ductile behaviour in a major earthquake without collapsing. Whilst the risk of shear failure in regions of large inelastic deformation can be largely reduced, the detailing requirements in capacity design often leads to reinforcement congestion that adds difficulty during the construction process, due to the high amount of transverse reinforcement required to provide shear resistance and confinement. The work presented in this paper forms a part of a wider research programme that aims to simplify the detailing requirements of transverse reinforcement in the joint and plastic hinge regions of moment-resisting frame structures. To this end, damage-tolerant concrete known as engineered cementitious composite (ECC) was used to substitute concrete in these critical regions. In this article, the results of reversed cyclic tests on two half-scale exterior beam-column joints, constructed with ordinary concrete and ECC, are presented. Key features of the response such as the reversed cyclic hysteresis loops, stiffness degradation and cumulative energy dissipation are discussed, along with crack development under reversed cyclic loading in the form of digital strain maps.

Neutron imaging software tools at the Oak Ridge National Laboratory

Over the past decade, Oak Ridge National Laboratory developed neutron capabilities at both the High Flux Isotope Reactor and the Spallation Neutron Source. A broad scientific portfolio has flourished at both facilities such that a new facility named VENUS is currently under construction at the Spallation Neutron Source. With a large range of applications, comes a broad range of user expertise regarding data processing, analysis, and visualization. Our team has developed and implemented a suite of tools to respond to all user needs. These tools span from data reduction, normalization, general tools such as organization of data folders, pre-processing of data, etc., to strain mapping, neutron grating interferometry, and advanced reconstruction algorithms for computed tomography. This manuscript provides an overview of some of the aforementioned tools.

Synchrotron X-ray diffraction and radiography - Lattice strain characterization in thin-walled carbon fibre channel structures subjected to buckling

Carbon fibre composites are widely used in low specific stiffness and high strength structures such as airframes. Compressive loading of these assemblies can lead to buckling and localised deformation around defects and imperfections that can hinder performance and lead to overengineering via excessive safety factors. Synchrotron X-Ray Diffraction (SXRD) has recently been shown to be capable of performing lattice strain mapping within carbon fibre composites at the microscale, a previously unprecedented resolution. In this study SXRD and radiography was performed on carbon fibre composite columns produced via two different methods (standard lamination and half square) at a range of different load states: unbuckled, one-third of the buckling load and post buckling. The results provide quantitative insights into the impact of these different production methods on lattice strain and fibre orientation, as well as the influence these factors have on reducing buckling load (by up to 22%). As well as being the first use of SXRD on industrially representative full-size carbon fibre samples, these insights provide invaluable detail into the factors which limit performance and the origins of column failure; crucial factors required to optimise structural design, production and loading capability.

Neutron Bragg edge tomography characterisation of residual strain in a laser-welded Eurofer97 joint

Nuclear fusion is a potential source of electricity which can address the environmental problems posed by fossil fuels. Eurofer97 steel is a primary structural material for breeding blanket and divertor components in fusion Tokamaks. Assembling and maintaining the structural integrity of these in-vessel components requires remote joint techniques, such as laser welding, although it induces immersive residual stress. The interaction of the residual strain and the heterogeneous microstructure degrades the mechanical performance of fusion components. However, an inspection of bulk residual strain distribution is still challenging. This study presents the residual strain distribution in the bulk of the weldment using volumetric tomographic reconstruction. A neutron Bragg edge imaging technique is used to obtain 2D angular projections. The 3D volumetric strain map is reconstructed from 2D residual strain projections using the filtered back projection technique. It is found that the laser welding technique generates a uniform residual strain field in the through-thickness direction. The results also demonstrate the potential of reconstructing volumetric residual strain distribution in bulk materials using fewer projections to reduce data redundancy and acquisition time for the neutron Bragg edge imaging technique.

Relation between sampling, sensitivity and precision in strain mapping using the Geometric Phase Analysis method in Scanning Transmission Electron Microscopy

The sensitivity and the precision of the Geometric Phase Analysis (GPA) method for strain characterization is a topic widely discussed in the literature and is usually difficult to quantify. Indeed, the GPA precision is intricately linked to the resolution of the strain maps defined when masking the periodic reflections in Fourier space. In this study an additional parameter, sampling, is proposed to be analyzed regarding the precision of GPA by developing the concept of a phase noise in the GPA equations. Both experimentally and theoretically, the following article demonstrates how the precision, and the sensitivity of the GPA method is improved when using a larger pixel spacing to record an electron micrograph in Scanning Transmission Electron Microscopy (STEM). The counterintuitive concept of increasing the field of view to improve the GPA precision results is an extension of the application of strain characterization methods in STEM towards low deformation levels.

(Invited) Advanced Carbon Nanotube Fluorescence Spectrometry for Novel Applications

Instrumental advances in near-IR fluorescence spectroscopy are enabling new types of measurements involving single-wall carbon nanotubes (SWCNTs). Two unique systems will be described. The first is a two-dimensional fluorescence-detected circular dichroism (FDCD) spectrometer. In this, SWCNT samples are excited by a spectrally selected supercontinuum laser beam that is switched between left- and right-circular polarization in an electro-optic modulator. Near-infrared sample fluorescence emitted in the backward direction is captured and directed to a scanning monochromator with a cooled InGaAs single-channel detector. After amplification and high precision digitization, the modulated signal component is extracted by computer-based phase sensitive detection. The system can measure a sample’s E22 circular dichroism in four spectral modes: 1) conventional FDCD, with scanned visible excitation wavelength and spectrally integrated (zero-order grating) emission detection; 2) Emission-specific FDCD, with scanned visible excitation wavelengths and selected emission wavelength; 3) Emission-scanned FDCD, with selected visible excitation wavelength and scanned emission wavelengths; 4) Excitation-Emission FDCD, with excitation and emission wavelengths both scanned to give two-dimensional data sets. This instrument can spectroscopically resolve enantiomer signals from a single (n,m) species in a racemic SWCNT sample.In a parallel project, developments in SWCNT fluorescence spectrometry are advancing nanotube-based strain measurement technology toward commercialization. Because SWCNT emission wavelengths vary systematically with axial strain, nanotubes in a thin coating on a specimen can serve as optically interrogated strain gauges. We apply this effect to measure strain maps through hyperspectral imaging of SWCNT fluorescence. A rotated band pass filter is used to capture a set of images in multiple spectral slices, from which a custom computer program deduces strain at each of ~105 image pixels and compiles strain maps. We will describe how this apparatus has evolved from a lab prototype into a compact portable system that can make measurements in industrial settings.

(Invited) Understanding Strain and Deformation in 2D Materials Via 4D-STEM and Cryo-EM

Strain and deformations play a critical role in the mechanical, electrical, and chemical properties of two-dimensional (2D) materials due to their atomic thinness. This presentation will discuss using the state-of-the-art transmission electron microscopy (TEM) techniques to study the strain and deformations in 2D materials. First, the speaker will introduce the study of strain relaxation in epitaxial lateral heterojunctions of 2D transition metal dichalcogenides (TMD) using nano-beam four-dimensional scanning TEM (4D-STEM)1. By developing an unsupervised learning approach, we were able to accelerate and automate the method for more general users2. In addition, the speaker will also present the direct visualization of the floppiness of 2D DNA origami using cryo-EM. The work uncovers flexible arms in 2D cross tiles, as well as clusters and stacks, which may potentially affect the assembly of DNA origami3. Han, Y. et al. Strain Mapping of Two-Dimensional Heterostructures with Subpicometer Precision. Nano Letters 18, 3746–3751 (2018).Shi, C. et al. Uncovering material deformations via machine learning combined with four-dimensional scanning transmission electron microscopy. Npj Comput Mater 8, 114 (2022).Ni, H. et al. Direct visualization of floppy two-dimensional DNA origami using cryogenic electron microscopy. Iscience 25, 104373 (2022).

Experimental investigation of single and butt-welded GFRP filament winding tubes bending behavior based on conventional and Digital Image Correlation method

Composite joints have become increasingly popular in pipeline assembly, replacing conventional fasteners. However, butt-welded joint composite techniques still need further structural study. This paper aims to study the flexural mechanical performance of the above mentioned composite joint method. Four-point bending tests were conducted on both unassembled (single) and two butt-welded tube types (based on NFT and DIN standard methods). In this context, the 2D digital image correlation (DIC) technique was applied during these tests to analyze the damage scenario based on full-field strain mapping. To further visualize the microscopic damage modes, X-ray tomography observations were conducted on both single and butt-welded specimens. The experimental results show that single tubes have the highest mechanical properties, with quasi-elastic behavior until the occurrence of fracture. The NFT butt-welded composite tubes present the maximum flexural stiffness and strength compared with the DIN tubes. It has also been shown that the strain distribution depends on the specimen configuration. The DIC analysis results show that the damage scenario is divided into two events: the onset of fracture and then the fracture propagation. These results were confirmed through microscopic inspections.