Background: Trabecular-bone adaptation (TBA) continuously reshapes the trabecular-bone (TB) microstructure at the microscale in response to mechanical loading. While organ-scale adaptation has been extensively studied, the mechanisms governing the evolution of individual trabeculae remain inadequately understood. Methods: This study proposes a new remodelling model: under finite remodelling capacity, surface regions that satisfy mechanostat criteria compete for remodelling events according to the spatial non-uniformity of local mechanical stimulus. This model uses a two-criteria remodelling scheme that combines (i) a mechanostat criterion for bone formation and resorption and (ii) a distance-weighted non-uniformity criterion. The model is implemented with a 2D finite-element framework using a USDFLD subroutine in the Abaqus/Standard software package. Idealised X- and I-shaped trabecular geometries are subjected to controlled bending, compression, and shear load cases to examine loading-dependent morphology evolution. Results: Compared with the corresponding one-criterion models, the two-criteria framework produces a lower fraction of active remodelling surface and a more clearly bounded convergence process. The numerical simulations reproduce characteristic plate-like morphologies of trabeculae under bending and rod-like morphologies under compression, while additional variations in thresholds and loading conditions shift the response towards resorption-biased structures. Conclusions: The results indicate that the mechanostat criterion primarily stabilises the global bone mass, whereas the non-uniformity criterion governs where remodelling is preferentially located on the trabecular surface. The proposed framework therefore provides a microscale and mechanistically interpretable basis for analysing loading-dependent morphological adaptation of individual trabeculae.

Longitudinal HR-pQCT scans can identify mineralised-tissue gains and losses after image registration, but whether baseline trabecular architecture can rank the locations of subsequent image-derived transitions remains unclear. This study tested whether surface-conditioned local trabecular support can rank subsequent formation-labelled transitions directly from baseline images and whether a longitudinal axial-prolate neighbourhood provides additional information beyond the isotropic local support. Baseline and 6-month distal-tibia HR-pQCT scans of nine postmenopausal women are analysed, giving 18 side-level image pairs. The analysis is restricted to baseline surface-marrow voxels, defined as marrow voxels sharing a face with baseline bone. A spherical support count provides an isotropic local-BV/TV-equivalent baseline. The proposed axial-prolate operator counts baseline bone voxels within an ellipsoidal neighbourhood, with its long axis aligned with the scanner's z-axis. Ranking performance is evaluated using leave-one-subject-out ROC-AUC. The obtained results indicate that the spherical local support ranks subsequent formation-labelled transitions above chance, showing that an isotropic local bone amount already contains prospective surface-conditioned information. The axial-prolate operator further improves this process. Matched-volume comparisons show that both anisotropy and longitudinal orientation contribute to this gain, while local-BV/TV-stratified analyses indicate that the directional signal is not fully reducible to the isotropic local bone amount. These findings establish an image-derived framework for ranking trabecular formation-labelled transitions from the baseline architecture alone. The distal-tibia application indicates that site-informed directional kernels can refine the general local-support framework. External validation is required to determine whether the kernel scale and alignment should be recalibrated for other anatomical sites and populations.

Exercise is widely recommended to maintain lumbar bone mineral density (BMD), the tissue-level mechanical environment generated within the lumbar spine during different exercises remains difficult to assess in vivo. This study integrated individualized musculoskeletal modelling, finite element analysis, and longitudinal quantitative computed tomography (QCT) to characterise exercise-specific lumbar loading patterns and interpret them alongside regional BMD adaptation. Ten postmenopausal women with low BMD who completed a 6-month combined exercise intervention were included (ChiCTR2400081574). QCT scans were acquired at baseline and follow-up to quantify BMD changes in the vertebral body (VB) and posterior region (PR). Individualized musculoskeletal models of walking, heel drops, jumping, and resistance exercise were developed to estimate joint reaction forces and muscle forces. These loads were transferred to individualized lumbar finite element models using a MATLAB–Python workflow to calculate segmental and regional von Mises stresses. Longitudinal QCT revealed that BMD was preserved or increased in the VB, whereas BMD declined in the PR, particularly at L1–L3. Jumping produced the highest peak joint reaction forces and von Mises stresses in the superior lumbar segments, whereas resistance exercise generated the greatest loading at L4–L5. Across all tasks and vertebral levels, von Mises stresses were consistently higher in the VB than in the PR. Distinct exercise modalities generated different segmental and regional loading environments within the lumbar spine. These mechanical patterns were broadly consistent with the observed regional BMD changes, providing a mechanically informed interpretation of lumbar bone adaptation during exercise. Chinese Clinical Trial Registry, ChiCTR2400081574 (retrospectively registered 5 March 2024).

The mechanical interaction at the limb–socket interface is a critical determinant of user comfort and skin integrity; however, the specific contributions of the coefficient of friction (μ) and Poisson’s ratio (ν) have not been quantitatively established. Objective: The objective of this work is to evaluate how μ modulates stresses in the residual limb and its potential association with socket safety, and to determine how ν governs socket maximum stress and structural safety margins. Methods: Above-knee finite-element (FE) model (elastic-plastic socket/base, first-order Ogden limb, rigid femur; C3D4H mesh) with parametric sweeps of μ (0.30–1.00) and ν (0.10–0.49) across polyethylene (PE), polyethylene terephthalate glycol (PETG), and high-performance carbon-fiber-reinforced polymers (HCFRPs). Results: Residual limb soft-tissue maximum Von Mises stress showed a U-shaped dependence on μ with a minimum near 0.7; the socket stress-to-yield ratio was largely insensitive to μ but differed by material (largest margin for HCFRPs, intermediate for PETG, smallest for PE). Increasing ν reduced socket maximum Von Mises stress by ~16–18% from 0.10 to 0.50 for all materials, with the ranking of safety margins (HCFRPs > PETG > PE) consistent with that observed in the μ analysis. Conclusions: Specifying a mid-range μ (~0.7) together with socket materials of higher ν (0.40–0.50) constitutes an effective strategy to reduce soft-tissue stresses while preserving structural safety, thereby offering biomechanical criteria for liner selection and material specification.

Transcatheter aortic valve implantation (TAVI) is a revolutionary intervention for aortic stenosis, yet complications such as paravalvular leakage (PVL) and excessive tissue stress remain prevalent, particularly in anatomies with elliptical aortic roots. This study develops geometric optimization strategies—specifically stent oversizing and lesion-specific design—to enhance sealing performance and reduce adverse mechanical interactions. A patient-specific finite element model of the aortic root was developed from CT imaging, and various stent designs were simulated, including alterations in strut thickness, width, and length. The evaluation compared conventional and modified stent configurations under standardized deployment conditions, including the effect of oversizing. Key metrics such as stress distribution, annulus gap area, and stent–aorta contact were particularly analyzed to assess device performance. A correlation analysis was conducted to identify interdependencies among the structural stiffness of the stents and deployment behaviors. Findings highlight the trade-offs between expansion, sealing, and mechanical response, emphasizing that tailored stent designs—particularly those with localized strut modifications—can achieve improved balance in anatomically challenging cases. The computational framework established in this study supports future TAVI optimization by linking stent design to patient-specific deployment outcomes.

Additive manufacturing enables the fabrication of patient-specific self-expanding Nitinol stents. However, the relationships among processing conditions, microstructural evolution, multi-scale mechanical behaviour, and in vitro deployment performance remain poorly understood. This study carried out microstructural, mechanical and functional assessments for personalised Nitinol stents produced by micro-laser powder bed fusion (μ-LPBF). The as-printed Nitinol exhibited a predominantly equiaxed microstructure with low porosity. The austenite finish temperature remained below body temperature, indicating stable austenitic behaviour under physiological conditions. Mechanical testing further revealed a measurable superelastic response with ~3% recoverable tensile strain. Electrochemical polishing transformed a particle-covered surface into a glossy finish for the as-printed stents, with the arithmetic mean roughness (Ra) being reduced to an average value of 1.89 ± 0.60 μm. The personalised μ-LPBF stents exhibited enhanced luminal restoration during in-vitro deployment, with local expansion exceeding that of the conventional design by up to 16.84%. These results demonstrate that the personalised μ-LPBF Nitinol stents achieve improved in-vitro luminal restoration compared with the conventional geometry.

Osteoporosis often leads to a site-specific vertebral fracture due to the regional heterogeneity of mechanical competence. High-impact combined with resistance exercise showed promise in improvement of volumetric bone mineral density (vBMD) at global spine-segment level. However, localized effects of such exercise on bone mineral density and mechanical strength remain under-explored. Thirty healthy postmenopausal women with low bone mass were recruited in randomized clinical trial of 6 months of high-impact and resistance exercises (ChiCTR2400081574). A voxel-based 3D registration method was designed to extract the identical seven anatomical sub-regions from QCT images scanned before and after this exercise. Seven finite-element models of each sub-region were developed to analyze the regional change of ultimate compressive strength (UCS) for the first time. Regionally, significantly lower changes of BMD were observed in the exercise group (EG) than the control group (CG) in the inferior articular process, transverse process, and anterior vertebral body (p < 0.05), although the BMD losses were found in both groups. While significant increases of UCS (up to 4.58

Trabecular-bone adaptation (TBA) is a continuous process, adjusting bone morphology against external loading and driven by mechanical stimuli. Various stimulus types such as strain energy density (SED) and stress magnitude were extensively studied. However, the in silico quantification and comparison of local trabeculae morphology caused by different mechanical stimuli, especially the parts of decomposed SED remains underexplored. This study introduces a 3D finite-element (FE) model to simulate mechanically driven TBA, with the aim to quantify the results of TBA models with different mechanical stimuli. Utilizing FE software ABAQUS with user-defined subroutines, the models simulate the trabeculae evolution under mechanical load. The outcome for the total SED, deviatoric SED and von Mises stress are compared, quantified with morphometric parameters of TB structure. The results show that the total first stimulus with equally weighted hydrostatic and deviatoric components demonstrates a higher resorption tendency compared to the deviatoric SED. This could be explained by its higher - quadratic - dependence on effective stress, while the results for the models based on von Mises stress are related to this stress linearly. This work advances the understanding of contribution of different mechanical stimuli to the TBA process at single-trabeculae level, offering insights into the trigger mechanism of trabecular-bone adaptation.

Trabecular bone is a living material that adapts its spatial organisation and mechanical properties when subjected to loading. There were efforts to describe adaptation in trabecular bone with mathematical models regulating resorption and formation activities as a function of mechanical stimuli. In this paper, an approach to optimise parameters of a bone-adaptation model is proposed and investigated, and the simulation results of trabecular-bone adaptation are quantitatively compared with high-resolution peripheral quantitative computed tomography (HR-pQCT) scans of a distal tibia in a participant following six months of physiological loading. For this purpose, finite-element models were developed from baseline scans of the participant's trabecular bone and used as an initial domain to run simulations regulated by the bone-adaptation model implemented in a Fortran subroutine. The simulated results were element-by-element compared with the corresponding models from follow-up HR-pQCT scans. Mechanostat parameters of the bone-adaptation model were optimised to improve correspondence between the simulated and follow-up HR-pQCT-based models. The developed approach captured the main trends in changes of bone volume fraction, trabecular thickness and separation and achieved 84 - 93 % of the element-by-element correspondence with the experimental models when utilising the optimised values of bone-adaptation parameters. These optimised values were different across the bone's cross-section. In the boundary conditions representing physiological loading, they predicted higher bone resorption rate in the inner regions of distal tibia than in the outer regions, intensified bone resorption in the anterior-inner, medial-inner and medial-outer regions, higher bone formation rate in the outer regions of distal tibia than in the inner regions, and intensified bone formation in the lateral-outer region.

BACKGROUND:The anterior talofibular ligament (ATFL) and the calcaneofibular ligament (CFL) are vulnerable to be torn or ruptured during lateral ankle sprain (LAS), especially in people with chronic ankle instability (CAI). This study aims to determine whether landing with a larger toe-out angle would influence ATFL and CFL strains in people with CAI, aiming to contribute to the development of effective landing strategies to reduce LAS risk. METHODS:Thirty participants with CAI (22 males and 8 females, age: 21.2 ± 1.2 years, height: 176.9 ± 9.0 cm, body mass: 70.6 ± 12.1 kg, mean ± SD) were recruited. Each participant landed on a specialized trap-door device with their unaffected limbs on a support platform and their affected limbs on a movable platform, which could be flipped 24° inward and 15° forward to mimic LAS conditions. Two landing conditions were tested-i.e., natural landing (NL, with natural toe-out angle at landing) and toe-out landing (TL, with toe-out angle increased to over 150% of that under the NL conditions). Kinematic data were captured using a 12-camera motion analysis system, and ATFL and CFL strains were calculated using a 3D rigid-body foot model. Paired sample t tests and Pearson's correlations were used to analyze data. RESULTS:Compared to NL conditions, ATFL strain decreased (p < 0.001, d = 2.42) while CFL strain remained unchanged (p = 0.229, d = 0.09) under TL conditions. The toe-out angle was negatively and strongly correlated with ATFL strain (r = -0.743, p < 0.001) but not with CFL strain (r = 0.153, p = 0.251). Compared to NL conditions, participants exhibit a lower ankle inversion angle (p < 0.001, d = 0.494), a higher plantarflexion angle (p < 0.001, d = 1.101), and no significant difference in external rotation angle (p = 0.571, d = 0.133) under TL conditions. CONCLUSION:Toe-out landing may reduce ATFL strain while maintaining CFL strain in people with CAI, thereby reducing the risk of LAS.

Aims: This study uses finite element analysis (FEA) to compare intramedullary nail (IMN) and locking compression plate (LCP) in tibiotalocalcaneal arthrodesis (TTCA), examining biomechanical changes in the joints and assessing which construct better supports arthrodesis under axial loading. Methods: A 3D finite element model of the foot-ankle complex was constructed from CT images of a 29-year-old male’s lower limb. The model included homogeneous cortical and trabecular bones, cartilage, and 29 ligaments. Titanium alloy (Ti6Al4V) implants simulated IMN and LCP fixations. The inferior surfaces of the metatarsals and calcaneus were fixed, and axial loads of 1×, 2×, and 3× body weight (BW) were applied. Von Mises stress and joint displacement evaluated construct stability. Results: At 1× BW, the IMN model exhibited the highest joint surface stress (32.44 MPa, superior talus) and higher implant stresses than those of the LCP model. Under increased loading, stress rose substantially in both models, peaking at +364.38% in LCP (superior talus) and +130.98% in IMN screws. Stress in the LCP model was more widely distributed across the tibia and calcaneus, while in the IMN model it was concentrated in the talus. At 3× BW, the LCP calcaneus exhibited the largest proportion of elements within the elevated stress range (5.3%). Peak displacement was higher in LCP (376 μm at 1× BW). Although IMN showed larger relative displacement increases, absolute joint displacements remained consistently lower than LCP. Conclusion: Both IMN and LCP provide sufficient mechanical support for TTCA. IMN offers greater initial stability, reflected by lower joint displacement, but generates higher implant stress, particularly under increased loading. In contrast, LCP exhibits more uniform stress distribution and smaller screw stress increases as load rises, and may offer improved mitigation of implant stress concentrations under elevated loads. Cite this article: Bone Joint Res 2025;14(11):1033–1044.

Presently, interfacial intermetallic compounds play a vital role in determining the reliability of solder joints due to their intrinsic mechanical property. Especially for Zn-Al solder joints, the interfacial Cu-Zn IMCs grow significantly without diffusion barriers. This work comprehensively investigated the mechanical properties of interfacial IMCs in Zn-Al solder joints with and without the Ni-W-P diffusion barrier by nanoindentation tests and first-principles calculations. The nanoindentation results show that the elastic moduli of CuZn4, Cu5Zn8, CuZn and Al3Ni2 were 68.45 +/- 1.4 GPa, 142.6 +/- 2.3 GPa, 94.7 +/- 1.16 GPa, and 221 +/- 18.9 GPa, respectively. Their corresponding hardness were 1.03 +/- 0.04 GPa, 5.98 +/- 0.23 GPa, 1.38 +/- 0.16 GPa, and 17.7 +/- 0.16 GPa. Through first-principles calculations, the bulk modulus of CuZn and Cu5Zn8 exhibits isotropic behaviour, while CuZn4 and Al3Ni2 demonstrate anisotropy. In addition, the bulk modulus, shear modulus, Young's modulus and hardness values of Al3Ni2 are considerably higher when compared to those of Cu-Zn intermetallic compounds.

Abstract Background Patients with knee osteoarthritis (KOA) are at high risk for falls, which is attributed to their impaired balance control. Identifying factors associated with balance control facilitates the development of precise KOA rehabilitation programs. This study was to investigate the correlations of balance control with proprioception, plantar tactile sensation (PTS), pain, joint range of motion (ROM), and strength among older adults with and without KOA, as well as the magnitudes and sequence of correlation of these factors to balance control. Methods A total of 240 older adults with (n = 124, female: 84, age: 68.8 ± 4.0 years) and without (n = 116, female: 64, age: 67.9 ± 3.5 years) KOA were recruited and assigned to the KOA and control groups. Their proprioception, PTS, pain, ROM, and strength were measured. Pearson or Spearman correlations were used to test whether they were significantly related to their Berg Balance Scale (BBS), and factor analysis and multivariate linear regression were used to determine the degrees of correlation between each factor and the BBS. Results Compared to the control group, the KOA group had lower BBS score, larger proprioception and PTS thresholds, smaller ROM, and less strength (p: 0.008, < 0.001–0.016, < 0.001–0.005, < 0.001–0.014, and < 0.001–0.002, respectively). In the KOA group, the BBS was weakly to moderately correlated with proprioception, PTS, pain, ROM, and strength (r: 0.332–0.501, 0.197–0.291, 0.340, 0.212–0.508, and 0.236–0.336, respectively). While in the control group, the BBS was correlated with proprioception and strength (r: 0.207–0.379, and 0.212–0.410). In the KOA group, BBS = 54.41+ (0.668*strength) - (0.579*PTS) - (1.141*proprioception) + (1.054* ROM) - (0.339*pain). While in the control group, BBS = 53.85+ (0.441*strength) - (0.677*proprioception). Conclusion Worse proprioception and PTS, smaller ROM, and less strength were detected among older adults with KOA, and their proprioception, PTS, pain, ROM, and strength were all related to balance control. Proprioception had the strongest correlations, followed by ROM, strength, pain, and PTS. Precise KOA rehabilitation programs may be proposed following the sequence of improving the five factors.

BACKGROUND:Bone is a living material that, unlike man-made ones, demonstrates continuous adaptation of its structure and mechanical properties to resist the imposed mechanical loading. Adaptation in trabecular bone is characterised by improvement of its stiffness in the loading direction and respective realignment of trabecular load-bearing architecture. Considerable experimental and simulation evidence of trabecular bone adaptation to its mechanical environment at the tissue- and organ-levels was obtained, while little attention was given to the trabecula-level of this process. This study aims to describe and classify load-driven morphological changes at the level of individual trabeculae and to propose their drivers.METHOD:For this purpose, a well-established mechanoregulation-based numerical model of bone adaptation was implemented in a user-defined subroutine that changed the structural and mechanical properties of trabeculae based on the magnitude of a mechanical stimulus. This subroutine was used in conjunction with finite-element models of variously shaped structures representing trabeculae loaded in compression or shear.RESULTS:In all analysed cases, trabeculae underwent morphological evolution under applied compressive or shear loading. Among twelve cases analysed, six main mechanisms of morphological evolution were established: reorientation, splitting, merging, full resorption, thinning, and thickening. Moreover, all simulated cases presented the ability to reduce the mean value of von Mises stress while increasing their ability to resist compressive/shear loading during adaptation.CONCLUSION:This study evaluated morphological and mechanical changes in trabeculae of different shapes in response to compressive or shear loadings and compared them based on the analysis of von Mises stress distribution as well as profiles of normal and shear stresses in the trabeculae at different stages of their adaptation.

Transcatheter aortic valve implantation (TAVI) has become a key treatment for severe aortic stenosis, especially for patients unsuitable for surgery. Since its introduction in 2002, TAVI has advanced significantly due to improvements in imaging, operator skills, and device engineering. Despite these innovations, challenges in device sizing and positioning remain, complicating outcome predictions. Computational modelling is a powerful tool to aid TAVI device design and to understand its interactive behaviour with the aortic root during the deployment. Previous studies often simplified tissue properties, neglected patient-specific geometries or omitted crucial elements such as leaflets and fabric. This paper presents a numerical framework capable of simulating the whole crimping and deployment process of a full TAVI device in a patient-specific aortic root including the native leaflets and calcifications. We conduct a comprehensive investigation into the mechanical behaviour of the TAVI and its interactions with patient-specific aortic root through dynamic finite element analysis during the deployment process, with validation against experimental results. Additionally, we examined the influence of applied pressure during balloon inflation on the interactive dynamics of the entire model. The study concludes that selecting optimal balloon pressures is crucial for enhancing TAVI device performance and reducing complications. Numerical simulations demonstrate that appropriate balloon pressure ensures sufficient flow area and effective contact pressure between the TAVI and the aortic root, while minimising deformation and the risk of paravalvular leak.

A conventional way to design and manufacture prosthetic sockets is labor-intensive and time-consuming, as such products are tailored to individual users. Achieving the desired and comfortable fit relies on a prosthetist's expertise and a patient's feedback. To digitalize this process, computer aided design (CAD) methods have been used recently to design the prosthetic socket while novel manufacturing methods such as Additive Manufacturing (AM) have been employed to increase time efficiency. Mechanical performance of products manufactured with this approach is still not fully understood. In this study, above-knee prosthetic sockets were printed with a material-extrusion 3D printing technique using various printing paths with an increased inter-layer contact area. Compliance of AM PLA prosthetic sockets to safety regulations, as described in the BS EN ISO 10328:2006, was achieved, while at the same time the conventional path sockets were outperformed. Understanding the material behavior at the inter-layer bond is a step towards reduced manufacturing times and increased mechanical performance.

Recent studies have contested long-standing assumptions that mechanical anisotropy is caused by weak interlayer bonding and demonstrated that microscale geometry (the groove between extruded filaments) is the major cause of anisotropy in extrusion additive manufacturing (AM). Inspired by those finding, this study investigates the potential for a new convention for print-path design to improve mechanical properties by setting extrusion width to be at least 250 % of nozzle diameter. The new convention enabled an almost 50 % improvement in mechanical performance, which was supported by finite element analysis data, whilst simultaneously reducing the printing time by 67 %. Whereas a typical extrusion AM part uses several side-by-side extrusions, here, three 0.4-mm-wide extrusions are replaced with a single extra-wide 1.2-mm extrusion; two 0.6-mm-wide extrusions are also studied. The contact area between layers of the extra-wide extrusion was 90 % as opposed to 63 % for the conventional approach. The improved contact area led to a 40–48 % enhancement of strength, strain-at-fracture and toughness. This study presents a compelling case for a methodological shift to extra-wide extruded-filament deposition and explains the underlying cause of anisotropic strength observed in previous studies. Two case studies demonstrate practical applicability for a print run of 1000 nylon visors and lower-limb polylactide prosthetic sockets, for which extra-wide filaments more than doubled load-bearing capabilities. Polylactide material was used for most of the study; potential for translation to other materials is discussed.

Trabecular bone undergoes changes in its morphology when subjected to external loading. This paper analyses changes in morphological parameters of individual trabeculae (trabecular thickness and bone volume fraction) in response to loadings at different directions: 0°, 20°, 45°, 70° and 90°. It was found that increase in the load incline caused increase in trabecular thickness and bone volume fraction. In addition, the equilibrium-state trabeculae obtained from adaptation to load at 90° (shear loading) had the highest axial and lateral stiffnesses, as compared to trabecular geometries obtained from other loading scenarios.