Brian K. Bay

Digital volume correlation (DVC) provides full-field three-dimensional measurements of internal deformation, but its accuracy and effective spatial resolution depend on image-processing and analysis choices. Here, we use fibrous, cartilaginous and mineralised tissues within a rat intervertebral disc (IVD) as a controlled multi-material case study, combining virtual compression with experimentally loaded synchrotron computed tomography images. We systematically evaluate phase retrieval and image filtering, bit-depth conversion, point-cloud design, subvolume size and strain-field smoothing. Stronger phase retrieval reduced correlation residuals while increasing displacement and strain errors, showing that residual minimisation alone can select poorer parameters. Image filtering sensitivity was greatest in fibrous tissue, which had the smallest characteristic image feature size, whereas inappropriate intensity mapping during 16-bit to 8-bit conversion preferentially degraded low-contrast cartilage. Increasing subvolume size, point spacing or strain-window size improved measurement robustness but progressively smoothed local strain heterogeneity. We demonstrate that the spatial resolution of strain measurement must be matched across tissue types in order to compare strain magnitude; in the IVD, matching DVC spatial resolution changed the apparent ratio of compressive strain among fibrous, cartilaginous and mineralised tissues from 3.1:1.9:1 to 14:7.7:1. These findings establish a sequential, deformation-based optimisation framework in which image characteristics guide processing, known deformations validate accuracy and strain fields are compared at matched measurement scales. The framework supports more reproducible and mechanically interpretable DVC analyses in heterogeneous biological and engineered materials.

An ideal prosthetic nucleus pulposus would combine flexibility with resistance to extrusion through annular defects. Prior unconfined compression and confined extrusion experiments have shown promising results with a hybrid composed of open-cell flexible polymer foam saturated with hydrogel. This study is a finite element parametric analysis to investigate mechanisms underlying the experimental results. In unconfined compression, decreasing the foam stiffness or increasing hydrogel permeability decreased the overall hybrid material stiffness as expected. However, in the confined extrusion configuration, decreasing the foam stiffness instead increased the hybrid stiffness due to densification of the foam as it was forced into the defect by the hydrogel. This localized densification mechanism provided by low stiffness foams suggests a useful, self-healing process in the presence of a defect, such as an annular tear.

Fibrous materials—ranging from connective tissues to engineered composites—are vital to many biological and man-made systems, optimised to withstand complex in-operando or in-vivo loading. The spine’s intervertebral disc’s (IVD) load-bearing capacity depends on a hierarchical extracellular matrix, where plywood-like lamellae of collagen fibres in the annulus fibrosus contain nanometre-scale fibrils built from staggered triple-helical monomers. How intact IVDs couple fibril-scale mechanics to fibre-scale organisation under load remains unresolved. Here we introduce TomoSAXS , a full-field 3D small-angle X-ray scattering tomography that maps fibril-to-fibre mechanics across an intact tissue. We show that intrafibrillar molecular pre-strain (D-period stagger) is lamellar textured and tightly correlated with microscale fibre strain. Pre-strain is inversely related to fibril strain and its variability, consistent with load-sharing through molecular unwinding. Radial strain bridges and high-curvature zones at the annulus fibrosus–nucleus pulposus interfaces emerge as critical regulators of local mechanics. These findings reveal concerted fibril–fibre interactions that sustain mechanical equilibrium in the IVD, preserving elasticity and shape. More broadly, TomoSAXS establishes a platform to visualise nano- to micro-scale matrix mechanics across biological and synthetic fibrous materials, with applications in ageing and disease, therapeutic evaluation, and the design of bio-based and bioinspired materials.

The function of all musculoskeletal joints depends on hierarchical structures spanning the molecular to whole joint scales. Investigating biomechanics across length scales requires correlative multiscale experimental methods. This study applies multimodal in situ synchrotron imaging techniques to spinal joints – focussing on the vertebral endplates – to explore relationships between structure and mechanical strain across spatial scales. Strain mapping using digital volume correlation combined with microarchitectural analysis reveals that high tensile and shear strains play a role in the cartilage to bone transition. Correlative imaging and diffraction show that bone contains narrower mineral nano-crystallites under greater compressive prestrain compared to calcified cartilage. We hypothesise that this multiscale structural adaptation supports the mechanical function of the intervertebral disc. Future applications of the techniques presented here have potential to help unravel biomechanical underpinnings of pathologies affecting mineralised tissue structure. The multiscale structure-function relationships uncovered here may inspire the design of biomaterials and orthopaedic implants.

Solid‐state welding of Al 1043 sheets is achieved via high‐pressure torsion (HPT) processing to produce bulk nanostructured Al disks. A homogeneous nanostructure without segregation is observed, with grain sizes of ≈430–470 nm. Miniature tensile testing, coupled with the digital image correlation (DIC) technique, is employed to determine the room‐temperature tensile deformation behavior, particularly the nonuniform behavior with necking, of the HPT‐bonded ultrafine‐grained (UFG) aluminum, comparing it with annealed coarse‐grained counterpart. The HPT‐bonded UFG Al exhibits a large fraction of post‐necking strain, which is supported by the estimated high strain rate sensitivity value of m = 0.085, suggesting the delay of local necking leading to tensile fracture. Detailed DIC analysis reveals prolonged diffuse necking, thus delaying local necking, in the HPT‐bonded UFG Al, while the annealed samples show high fractions of local necking during the nonuniform deformation. Moreover, the DIC data illustrate that local necking predominantly occurred at a limited neck zone, maintaining a plateau strain distribution at the out‐of‐neck zone throughout necking deformation toward tensile failure for both annealed and UFG aluminum. The DIC method offers an alternative means to demonstrate the transition in necking behaviors of materials by estimating the plastic lateral contraction exponent.

The cold angular rolling process (CARP) is being developed as a continuous severe plastic deformation technique, which can process metal sheets without any length limitations at room temperature. CARP contains cold rolling and equal‐channel angular process components. The sheet thickness is kept consistent before and after CARP, allowing multiple passes of the sheet. The desired microstructure and mechanical properties can be achieved in the processed metallic sheets. The current study is aimed to evaluate the capability of CARP by processing copper sheets with different sheet widths for repetitive passes. The CARP‐treated sheets are examined by lab‐scale X‐ray and high‐energy synchrotron X‐ray diffraction to investigate the evolution in dislocation density, texture, and strain anisotropy, and by tensile testing to identify the bulk mechanical properties. The digital image correlation method is applied to tensile testing so that strain localization within the sample gauge is visualized and deformation behavior is evaluated after yielding till postnecking by estimating the hardening exponent and strain hardening rate of the CARP‐treated sheet. Comparing the reported continuous and multiple‐step processes on Cu and its alloys, the present study confirms that the CARP is potentially a useful sheet process for strengthening ductile metals.

We intend to examine a simple, low-cost and innovative design– known as a “disc emulator”. This design (or the disk emulator) mimics the mechanical response of the motion segment (vertebra -intervertebral disc-vertebra) of the human spinal column under axial compression loads. The disc emulator consists of three parts: the upper, middle, and lower parts. The upper and lower parts

Imaging techniques for quantifying changes in the hierarchical structure of deforming joints are constrained by destructive sample treatments, sample-size restrictions and lengthy scan times. Here, we report the use of fast low-dose pink-beam synchrotron X-ray tomography in combination with mechanical loading at nanometric precision for in situ imaging, at resolutions below 100 nm, of the mechanical strain in intact untreated joints under physiologically realistic conditions. We show that in young, older and osteoarthritic mice, hierarchical changes in tissue structure and mechanical behaviour can be simultaneously visualized, and that the tissue structure at the cellular level correlates with the mechanical performance of the whole joint. We also use the tomographic approach to study the colocalization of tissue strains to specific chondrocyte lacunar organizations within intact loaded joints and to explore the role of calcified-cartilage stiffness on the biomechanics of healthy and pathological joints.