The biomechanics of the lung plays a crucial role in respiratory function, and its alteration is closely linked to the onset and progression of lung diseases. Quantifying local strain within lung tissue is essential for understanding how lung mechanics influence pulmonary function and disease progression. Digital Volume Correlation (DVC) provides a non-destructive method to quantify 3D strain fields in biological tissues, but its accuracy depends on multiple parameters, which remain poorly characterized in soft tissues. In this study, we evaluated the accuracy of DVC, using both local and global approaches, for lung tissue imaged with high-resolution contrast-enhanced computed tomography (HR CECT) and assessed its potential application throughout a range of lower resolution and noisier data towards HR ex vivo and in vivo microCT data. We investigated the effects of DVC settings, lung microstructure, and input image quality, including noise level and voxel size. Synthetic deformations of known magnitudes (1-5%) were applied to optimize subvolume and mesh sizes, with mean metric values and correlation residuals used to evaluate registration quality. Strain measurements from global DVC were highly sensitive to mesh size, with optimal meshes yielding robust estimates, while larger meshes reduced accuracy. Correlation residuals reliably identified the optimal mesh size as a global registration metric. Adding Gaussian noise demonstrated that higher noise levels reduced DVC accuracy, particularly at larger deformations and with non-optimal meshes. Downscaling imaging data increased voxel size in a range from 3.8 μm to 30.4 μm left central strain distributions largely unchanged, but induced boundary-related errors with regions of high strain intensity near sample boundaries highlighting the need for sufficiently large volumes of interest at large voxel sizes for DVC-based strain analysis. Within these limitations, DVC effectively captured regional lung strain, supporting its applicability from HR CECT data to ex vivo HR microCT. Our findings provide critical insights into how DVC operational parameters, across both local and global approaches, tissue microarchitecture and input imaging quality affect the accuracy of strain measurements in soft tissues. By demonstrating the feasibility of DVC for lung strain analysis using microCT data, this study provides a foundation for further research into the use of strain measurements to characterize lung biomechanics in animal models at study endpoints with ex vivo HR microCT.
Fascia forms a continuous connective tissue network throughout the body and is persistently subjected to complex mechanical loading, including stretching, compression, shear and torsion during daily activity. Growing evidence suggests that fascia is not merely a passive mechanical linkage for force transmission but may also participate in diverse physiological processes, implying its functional versatility. Such multifunctionality is likely governed by the coupling of multiple factors, yet the underlying biophysical properties remain incompletely understood. Here, we performed a systematic investigation of dried ex vivo fascial tissues from multiple anatomical regions of rats in two age groups (1-2-month and 12-month) using Piezoresponse Force Microscopy. We demonstrate that fascia exhibits measurable electromechanical coupling and that the effective piezoelectric coefficient is significantly higher in the 12-month group than in the 1-2-month group, whereas differences among anatomical regions within the same age group are comparatively small. Integrating the experimental observations with theoretical analysis suggests that the stronger effective electromechanical response may be associated with the presence of thicker collagen fiber bundles, and that the inclination angle of collagen bundles may also contribute to the overall effective electromechanical response. Together, these findings confirm the electromechanical coupling of fascia and link its magnitude to collagen morphology, providing a biophysical basis for understanding the multifaceted roles of fascia in physiological function and for addressing clinically relevant conditions associated with fascial morphological alterations.
Resin-based restorative composites containing ion-releasing particles usually present inferior mechanical properties in relation to conventional composites. The objective of the present study is to estimate the contribution of dicalcium phosphate dihydrate (DCPD) particle characteristics (morphology and intrinsic mechanical behavior) and the lack of chemical bond to the polymer matrix on degree of conversion (DC), composite flexural strength (BFS) and modulus (FM), and Knoop microhardness (KHN). Three series of materials were tested (25 in total), consisting of decreasing silanized barium glass (Gf) fractions and increasing fractions of non-silanized glass (Gnf), non-functionalized DCPD (Dnf), or 10-MDP-functionalized DCPD (Df). Composite DC was determined using near-FTIR (n = 4). BFS (n = 10) and KHN (n = 5) tests were conducted after 24 h storage in water. Stress distribution in the flexural specimen during loading was simulated by finite element analysis (FEA). Experimental data were analyzed by Kruskal-Wallis (DC) and one-way ANOVA/Tukey test (BFS, FM and KHN, α ≤ 0.05). Particle type and functionalization did not affect DC. BFS showed a higher effect of functionalization than particle type, explained by the stress concentration in the polymer around non-functionalized particles. For FM, functionalization with 10-MDP compensated for the lower elastic modulus of the DCPD particle. For KHN, particle type showed a stronger effect for both functionalization conditions. In conclusion, the low mechanical properties of DCPD-containing composites can be ascribed both to the intrinsic characteristics of the DCPD particles and the absence of an effective bonding to the polymer matrix.
In this study, a biphasic calcium phosphate cement (BCPC) was fabricated, combining the biocompatibility of hydroxyapatite (HA) and the biodegradability of β-tricalcium phosphate (β-TCP), and processed by robocasting, an extrusion-based technique, for bone tissue engineering applications. Despite its well-known biological performance, this material is brittle - mainly used as bone graft substitutes due to its limited mechanical strength. To overcome this limitation, graphene nanoplatelets (GNPs) were incorporated into the cement as a reinforcing filler. Their addition not only enhanced the mechanical strength but also improved the rheological behavior of BCPC pastes, resulting in better printability during the robocasting process. In particular, the incorporation of GNPs reduced the elastic modulus of the pastes, facilitating extrusion. Bars with and without microporosity were 3D-printed and subsequently evaluated by flexural testing. The flexural strength of microporous BCPC samples increased from 4.2 MPa (0% GNP) to 5.9 MPa (2% GNP), representing a 40% improvement. Although dense samples also exhibited higher strength with GNP addition, the difference was not statistically significant. Distinct stress-strain curve profiles obtained during bending tests revealed the influence of the printed architecture on the mechanical response of the printed parts. The flexural modulus followed the opposite trend to the flexural strength, showing a significant increase in dense parts containing GNP, while no substantial change was observed in the microporous counterparts. Overall, all measured mechanical properties fell within the range reported for trabecular bone substitution applications.
This study developed a dental composite resin incorporating KH-570-modified magnesium oxide nanoparticles (MgONPs) and methacryloxypropyl polyhedral oligomeric silsesquioxane (MAP-POSS), and evaluated its microstructure, physicochemical properties, antibacterial activity, and in vitro cytocompatibility. MgONPs were surface-modified with 3-(methacryloyloxy)propyltrimethoxysilane (KH-570), and composite resin specimens containing 2 wt% modified MgONPs with gradient additions of MAP-POSS were prepared, using a commercial composite resin as the control. Filler structure and modification were characterized by XRD and FTIR, and the composite resins were analyzed by SEM and FTIR. Depth of cure, Vickers hardness, water sorption, solubility, compressive strength, and flexural strength were measured. Antibacterial activity was evaluated against planktonic Streptococcus mutans (S. mutans) using the film contact method, and cytotoxicity was assessed using the CCK-8 assay with L-929 fibroblasts. Among the tested formulations, the specimen containing 4 wt% MAP-POSS and 2 wt% modified MgONPs exhibited the densest microstructure, the highest degree of conversion (83.03%), the greatest depth of cure and mechanical properties, a moderate reduction in viable planktonic S. mutans (R = 1.16), and no obvious cytotoxic response under the tested conditions. These results indicate that the combination of MAP-POSS and silane-modified MgONPs may be a feasible strategy for achieving balanced mechanical reinforcement and antibacterial functionality in dental composite resins.
Finite element (FE) models are widely used to investigate the mechanical behaviour of the human Intervertebral Disc (IVD), but their predictive capability strongly depends on the accurate calibration of multiple material parameters. This study proposes a surrogate-assisted optimization framework that integrates finite element modelling, machine-learning (ML) regression models and Genetic Algorithms (GA) to identify the material parameters governing a healthy lumbar intervertebral disc. A parameterized L3-L4 intervertebral disc FE model was constructed using eleven material parameters, which were systematically varied through a two-level fractional-factorial Design of Experiments (DoE). This yielded 128 finite element simulations under six standard loading scenarios, producing six stiffness responses and nine bulge deformations that were used to train surrogate regression models for all mechanical responses. The surrogate models showed excellent predictive capability for most responses, enabling efficient exploration of the high-dimensional parameter space without additional FE simulations, although slightly lower accuracy was observed in some stiffness-related outputs due to their higher complexity. GA-based optimization produced parameter sets that more accurately reproduced experimental reference data than those obtained using a previous Response Surface Methodology (RSM) approach. This improvement was reflected in a 15-20% reduction in normalized mean absolute error, with GA achieving values of 0.229-0.238 compared with 0.278-0.280 for RSM. The largest improvements were observed in bulge-related responses, although stiffness predictions also benefited from the GA approach. Overall, the results demonstrate that combining FE modelling with surrogate machine learning models and genetic algorithms provides a powerful and computationally efficient strategy for calibrating lumbar IVD FE models and improving agreement with experimentally observed mechanical behaviour. The proposed framework enhances accuracy, reduces computational cost and facilitates the development of more realistic biomechanical simulations with potential applications in spinal implant design, pre-clinical testing and patient specific modelling.
Human root dentin may undergo direct physicochemical, microstructural, and mechanical alterations during radiotherapy for head and neck cancer. In this study, healthy third molars were irradiated under tomotherapy-like conditions using a clinically inspired fractionated protocol of 2 Gy per day for 10, 20, and 30 days, reaching cumulative doses of 20, 40, and 60 Gy, together with a non-irradiated control group. Root dentin was characterized using Raman spectroscopy, atomic force microscopy, X-ray diffraction, scanning electron microscopy, and microtensile testing. Raman spectroscopy showed preservation of the main mineral and organic bands, but the CO3/PO4 and Amide I/PO4 ratios decreased with irradiation, indicating changes in the mineral-matrix balance. AFM showed no major nanoscale topographic alterations, although AFM showed heterogeneous local Young's modulus distributions, with higher central values in the irradiated groups but no statistically significant differences from the control. XRD confirmed preservation of the apatite phase without formation of new crystalline phases, while Rietveld refinement revealed subtle anisotropic lattice changes, particularly an increase in parameter a. SEM showed localized surface irregularities, less defined tubule borders, and partial tubular obstruction in selected irradiated fields. At the functional scale, microtensile testing revealed reductions in microtensile strength and strain at failure. These findings indicate radiation-associated multiscale alterations in root dentin, including relative changes in mineral-organic organization, localized microstructural differences, and reduced mechanical performance.
OBJECTIVES:To investigate whether printing temperature and the temporal distribution of irradiance during LCD-based vat photopolymerization influence the mechanical properties and interfacial behavior of printed photopolymer green bodies when the total radiant exposure is kept constant. MATERIAL AND METHODS:A modified LCD-printer equipped with a programmable LED illumination system enabling temporal irradiance modulation and integrated load-cell monitoring was used to fabricate green-body tensile specimens (N = 175) from a dental model resin. Specimens were printed at 22°C and 40°C using constant, linearly increasing, and linearly decreasing irradiance profiles with identical total radiant exposure. Elastic modulus (EM), fracture energy (FE), ultimate tensile strength (UTS), strain at break (SB), and separation force (SF) were determined before post-curing. Fracture surfaces were evaluated macroscopically and microscopically. Mechanical properties were analyzed using two/one-way ANOVA and Scheffé post-hoc testing (α = 0.05), whereas SF was evaluated descriptively. RESULTS:Printing temperature significantly affected all investigated mechanical properties (p < 0.001). Irradiance profile significantly influenced EM, FE, UTS, and SB, whereas significant temperature × irradiance interactions were observed for EM, UTS, and SB. Across both temperatures, the constant irradiance profile generally resulted in the highest values for the investigated mechanical properties, whereas the decreasing irradiance profile resulted in the lowest values. In contrast, decreasing irradiance consistently reduced SF compared with constant and increasing irradiance profiles. Fracture surface analysis revealed no systematic morphological differences between the investigated groups. SIGNIFICANCE:Temporal irradiance modulation represents an additional process parameter in LCD-based vat polymerization. Although it exerted only a limited influence on the investigated mechanical properties of green bodies, decreasing irradiance consistently reduced SF, indicating that the temporal distribution of radiant exposure affects interfacial behavior during layer formation. These findings may contribute to the further optimization of exposure strategies in LCD-based vat photopolymerization.
This work analyses the characterisation of hydrated/fresh human cortical bone tissue under Mode I fatigue-fracture. High-cycle fatigue tests under displacement control were performed using the double cantilever beam test. This procedure enables the identification of the coefficients of the modified Paris law and the fatigue threshold, i.e., the strain energy release rate below which the material theoretically has infinite life. To avoid the cumbersome and inaccurate monitoring of crack length during fatigue tests, an equivalent crack-length-based procedure was adopted for data reduction. A cohesive zone model for high-cycle fatigue was formulated specifically to account for the fatigue threshold locally, i.e., at the integration point, and was used to validate the experimental procedure. The model proved effective and was applied to five samples, and to overall results, thereby leading to the proposal of a modified Paris law that accurately represents the fatigue behaviour of this set of human femoral cortical bone, as well as the identification of its strain energy release rate at the threshold.
Single fiber studies are essential to the development, testing and evaluation of new actives, formulations, and technologies in hair care. However, these studies have been constrained by the highly variable nature of hair fibers, as well as difficulties in their handling, making single fiber research expensive, time-consuming, low-throughput, and difficult to replicate. In response to this unmet need, a new tool, the Single-Fiber Hair Holder (SFHH), has been designed and developed to expedite and broaden accessibility of single fiber imaging and analysis studies; the current report outlines the design features of the tool and proof-of-concept testing. This easy-to-use hair mounting system, by stabilizing and gently straightening single hair fibers, facilitates relocation of the same surface region of hair cuticle at the micrometer scale before and after application of treatments, across a diverse range of hair types. Use of the SFHH reduces sample preparation time to approximately 1 min, reduces laboratory consumables as it is a re-useable 3D printed mount, and optimizes study design by allowing relocation of up to three regions along a fiber. The SFHH represents a new frontier in methodology for single fiber studies as it provides a new, standardized tool that supports top-quality single fiber analysis within the cosmetic industry.
In structural and biomedical applications, where high-speed loading is a major concern for mechanical reliability, high-performance polymers (HPP) are increasingly required. Still, their thermomechanical response produced by additive manufacturing methods has not been fully characterized. In this study, the strain-rate-dependent compressive behavior of specimens, 3D printed by the material extrusion (MEX) method with the polyether ether ketone (PEEK) biopolymer, has been investigated. Simultaneously, the evolution of specimen temperature has been monitored using an infrared camera. Compression testing was performed over a range of test speeds up to 200 mm/min. The aim was to quantify the mechanical performance under compression loads and concurrently thermal self-heating phenomena as a function of applied strain rate. Results show that the compressive strength of the MEX-processed PEEK had a positive strain-rate sensitivity of 14.1% at higher strain rates. The strain-rate sensitivity index had higher values at lower test velocities, suggesting that viscoelastic effects play a larger role in the deformation mechanism. At the same time, the maximum specimen temperature increased by 33% as the strain rate increased (63 to 85 °C) (thermomechanical self-heating), which can affect material response at elevated strain rates. This work offers fundamental insights into the mechanical response of MEX-fabricated PEEK biopolymer under loads applied at various speeds and has direct merit for the design of additively manufactured biomedical components which are often subjected to such loading conditions.
Advancements in the research of natural biocomposites are enhancing the design of bioinspired materials. However, to determine safe operational limits for high-temperature engineering applications, it is essential to comprehensively understand their mechanical performance under thermal loads. This study examined the lattice expansion behavior and mechanical properties of the nacre and prismatic layers of heat-treated abalone shells. Anisotropic expansion along the three crystallographic axes was observed in aragonitic nacre at room temperature, which was associated with deformation of the V[CaO9] polyhedron. Several Ca-O bonds contributed to the deformation of this polyhedron. The prismatic layer also exhibited anisotropic expansion at temperatures up to 623 K. The V[CaO6] polyhedron underwent deformation, and the Ca-O bond within the polyhedron was associated with anisotropic expansion along the c-axis. The anisotropic expansion of the nacre relaxed at 473 K, whereas that of the prismatic layer persisted up to 623 K. Across all heat-treatment temperatures, nanoindentation measurements showed that the nanohardness of the prismatic layer exceeded that of the nacre. A similar trend was observed for the elastic modulus. A comparative analysis of the mechanical properties of the nacre and prismatic layers revealed that nacre has superior toughness, whereas the prismatic layer exhibits greater hardness. Both properties substantially deteriorated after heat treatment at 473 K.
Understanding the mechanical interactions between surgical probes and brain tissue is essential for optimizing procedures such as deep brain stimulation (DBS). In this study, agar gel phantoms were used as brain tissue surrogates for their well-characterized mechanical properties and extensive use in neurosurgical modeling. Systematic experiments were conducted to quantify the insertion and withdrawal forces of DBS probes, and the evolution of probe-induced channels was analyzed using synchronized high-speed imaging and force measurements. Key parameters, such as peak insertion force, were extracted from filtered curves showing the relationship between force and depth as well as force and time. Classical physical models, such as the Hertz and Fung equations, characterized the force response in the linear regime and in regimes with weak nonlinearity, while a hybrid physics-guided residual neural network (PGNN) was applied to capture complex and highly nonlinear interactions. Our results show that the force response exhibited time-dependent behavior: insertion force showed clear velocity dependence, whereas withdrawal force was predominantly described by a velocity-independent friction term over the tested range. Probe speed and gel-recovery dynamics nevertheless influenced channel closure. Channel measurements revealed that the residual channel is consistently smaller than the probe diameter, which can be attributed to the combined effects of elastic recovery, viscous flow, and hydration. Both probe speed and depth were found to significantly influence the dynamics of channel closure. Model fitting demonstrated that classical models can adequately describe the force response in specific regimes, but the hybrid PGNN model improves prediction accuracy for complex mechanical interactions. Overall, this work offers new insights into phase-specific probe-material interaction mechanics in a controlled homogeneous surrogate, and the integrated experimental and modeling framework developed here provides a baseline dataset for future studies of DBS-relevant insertion mechanics and model refinement.
With the development of artificial diet-based rearing technology, differences in rearing systems now affect the characteristics of silkworm (Bombyx mori) silk fibers. Forced reeling, a green and non-destructive modification method, has shown significant potential for the preparation of high-performance silk fibers. However, comparative studies on the characteristics of forced reeled silk fibers under different rearing systems are limited. The aim of this study was to compare and analyze the structure and properties of forced reeled silk fibers derived from a mulberry leaf-based rearing system (ML-FRs) and forced reeled silk fibers derived from an artificial diet-based rearing system (AD-FRs) under different reeling speeds. Silkworms reared on artificial diet exhibited better adaptability to forced reeling and AD-FRs exhibited higher strength, stiffness, and thermal stability than ML-FRs. When the reeling speed reached 40 mm/s, the tensile strength and Young's modulus of AD-FRs (712.29 ± 55.69 MPa and 16.10 ± 2.43 GPa, respectively) were higher than those of ML-FRs (649.60 ± 61.90 MPa and 14.45 ± 1.78 GPa, respectively). These results were attributed to the combined effects of differences in the adaptability of silkworms during forced reeling and changes in the secondary structure, crystallinity, and crystal orientation of the forced reeled silk fibers. This study revealed the mechanisms by which rearing systems and reeling speeds affect the structure and mechanical properties of forced reeled silk fibers, providing a theoretical basis and practical guidance for selecting rearing systems and reeling speeds to produce high-strength and high-modulus silk fibers when using forced reeling.
This study introduces an anisotropic energy limiter-based gradient damage framework designed to predict the failure of soft biological tissues under finite deformations. Traditional damage models often struggle with these materials due to their complex, anisotropic microstructures and highly nonlinear behavior. The proposed framework addresses these challenges by incorporating an anisotropic energy limiter function to control local damage evolution and a gradient-enhanced formulation that ensures mesh-independent results through a rate-dependent damage evolution law that accounts for the loading-rate sensitivity of soft biological tissues. A significant theoretical contribution of this work is the derivation of closed-form analytical solutions for anisotropic damage, which are used to verify numerical outcomes and facilitate model parameter fitting. To enhance computational performance, the authors also introduce a simplified plane stress version of the Holzapfel-Gasser-Ogden (HGO) model, which improves numerical efficiency and stability while mitigating locking issues during finite element method (FEM) simulations. The framework was validated through comparisons with experimental data from aortic specimens, analytical solutions, and published numerical benchmarks across 2D and 3D structures. The results show good agreement with the reference solutions and experimental observations, demonstrating that the model effectively captures progressive failure, strain softening, and anisotropic damage evolution, thereby providing an effective computational framework for the biomechanical simulation of soft tissue failure.
