Biomechanical Behavior Research Articles

Sports biomechanical analysis of knee joint injuries in table tennis players

Table tennis is a fast-paced, explosive sport that puts a lot of strain and stress on players’ lower limbs, particularly their knee joints. This work built a thorough mathematical model to investigate the dynamic and kinematic properties of the knee joint under various motion situations, with the goal of better understanding the biomechanical behavior of the knee joint in table tennis. A model of knee joint motion that takes into account the two degrees of freedom—flexion, extension, and rotation—is put forth based on the concepts of human biomechanics and kinematics theory. This model uses the Newton Euler equation to explain the mechanical behavior of the knee joint and integrates internal forces like muscle forces and external factors like ground reaction forces for torque balance analysis. This study offers a thorough examination of the force distribution and knee joint trajectory in table tennis using numerical simulation techniques. The findings show that the knee joint undergoes considerable compression and shear forces during intense activity, and that the joint’s stress properties vary significantly depending on the kind of movement. This finding is a valuable resource for table tennis players’ knee joint injury prevention and rehabilitation.

Gender-Based Differences in the Biomechanical Behavior of the Thorax During CPR Maneuvers.

In this study, 18 rib cages (8 males and 10 females) were segmented from computer tomography (CT) images. In order to analyze the potential differences in thoracic biomechanics during cardiopulmonary resuscitation (CPR), a set of numerical experiments was conducted using finite elements (FE). Compression forces were applied at different points on the rib cage. Results indicated that the optimal compression area for both sexes is the sternum at the 5th rib level, requiring the least force to achieve the desired compression depth. Males required greater force than females. Among females, those with lower width/depth ratios (more rounded thoracic shape) required less force compared to those with higher ratios (more oval-shaped thorax).

Ischemic Risks Induced by Larger Orthodontic Forces on Dental Pulp and Neuro-Vascular Bundle in Reduced Periodontium

Background/Objectives: There are few data about the ischemic risks induced by the large orthodontic forces during periodontal breakdown in dental pulp and neuro-vascular bundle (NVB) and none on the individual tissular stress distribution, despite their great importance for orthodontic treatment planning. Our aim was to assess, by a numerical analysis, the biomechanical behavior of dental pulp and the NVB during a simulated horizontal periodontal breakdown (1–8 mm), under 2–4 N of applied orthodontic forces and five movements (rotation, translation, tipping, intrusion, and extrusion). Additionally, the ischemic and degenerative-resorptive risks were assessed. Methods: The analysis involved 72 3D models of nine patients, totaling 720 simulations. The models were CBCT-based, having the second lower premolar and surrounding periodontium, and they suffered 1 mm of gradual horizontal periodontal breakdown (up to 8 mm loss). Results: Both forces displayed a similar qualitative stress distribution in all five movements, but with a quantitative increase (doubling of stress amounts for 4 N when compared with 2 N). The highest amounts of stress were displayed at 8 mm of periodontal loss, which is lower than the 16 KPa of the maximum hydrostatic pressure. The NVB stress was higher than the pulpal stress. Rotation was the most stressful, closely followed by tipping, intrusion, and extrusion. Conclusions: A total of 4 N of applied force seems to not induce any ischemic or degenerative-resorptive risks for healthy intact teeth, in up to 8 mm of periodontal breakdown. Intrusion and extrusion determined the highest visible tissular deformation in the NVB, with potential ischemic and resorptive-generative risks for previously traumatized/injured teeth (i.e., occlusal trauma). Rotation and translation (in particular) showed the highest coronal and radicular pulpal stress with potential ischemic and resorptive-generative risks for previously injured/traumatized dental pulp (i.e., direct-indirect pulp capping). It seems that 4 mm of periodontal breakdown could signal a clinical stress increase with potential ischemic and degenerative-resorptive risks for the previously traumatized/injured tissues.

Effect of the connection structure of zirconia dental implants on biomechanical properties

The connection structure of zirconia dental implants significantly influences their biomechanical behavior and plays a crucial role in the overall service performance of the implant system. This study aims to compare the stress distribution of zirconia implants featuring various internal connection structures under different working conditions. Four distinct types of connection structures were designed for zirconia dental implants: triangular, quadrilateral, hexagonal, and hexalobular plus connections. Additionally, the finite element method was employed to analyze these structures under three working conditions: a static load test model, a bone level model, and a torsion model. Results indicated that in the static load test model, the hexagonal structure experienced the highest stress value at 1284.9 MPa due to its thin neck wall, whereas the hexalobular plus connected implant exhibited the lowest stress value at 1252.9 MPa. In the bone level model, the triangular connection structure demonstrated poor stress distribution for cortical bone and cancellous bone at 69.606 MPa and 7.8191 MPa, respectively. Conversely, the hexalobular plus connection yielded superior stress results for cortical bone and cancellous bone, with values of 69.606 MPa and 7.8191 MPa, respectively. In the torsion model, the hexalobular plus-connected implant exhibits the highest stress value at 210.37 MPa, while maintaining the smallest force transmission angle. Therefore, given that the abutment necessitates a greater range of installation angles and improved torque transmission, the hexalobular plus connection structure may represent the optimal choice.

Evaluation of polyaryletherketone materials as post-core abutments for removable partial dentures: A finite element analysis

ObjectiveThe purpose was to compare the biomechanical behavior of single-piece post-core restorations made from polyaryletherketone materials with fiber post-core restorations when serving as abutments for RPD using finite element analysis (FEA). MethodsPhantom maxillary central incisor and mandibular second premolar were trimmed 1-mm coronally to cemento-enamel junction; root canals were enlarged and the teeth were scanned. Data was transferred to a solid modeling software.Twenty four models, including six post-core restorations:glass-fiber post/composite core (GFH/GFL) and single-piece post-core groups as, PEKK(PKH/PKL);Ti02-reinforced PEEK(TH/TL);ceramic reinforced PEEK(CeH/CeL);carbon fiber reinforced PEEK(CaH/CaL);glass fiber reinforced PEEK(GFPH/GFPL) with hybrid ceramic/lithium disilicate crowns on each tooth were constructed.Loads of 100 N for central incisor, and 300 N for premolar in a 45°oblique direction were applied to simulate masticatory forces. Clasp removal force of a RPD was simulated as 5 N vertically.FEA was employed to evaluate the von Mises stresses.Strain at cement layer was also investigated. ResultsCaH/CaL groups revealed the lowest stress for both teeth at root while TH/TL groups revealed the highest stress. The lowest stress values in the post-core were in GFH/GFL groups while the highest stress occurred in the CaH/CaL groups for both teeth. SignificanceGlass-fiber post-cores exhibited the lowest stresses in the post under masticatory and clasp removal forces. It may suggest a potentially lower risk of post fracture compared to polyaryletherketone group materials. TiO2-reinforced PEEK post-cores exhibited the lowest stresses among PAEK materials, indicating a potentially high fracture resistance.

Mechanobiology studies of bladder tumor cells using laterally squeezing microfluidic flow cytometry

The deformability and uptake capability of cells are critical indicators of their biomechanical properties and functional behaviors, particularly in tumor heterogeneity and cancer research. Here, we introduce a microfluidic flow cytometry platform integrated with a laterally adjustable squeezing structure for the characterization of bladder tumor cells (including 5637 and EJ cell lines) and uroepithelial cells (SV-HUC-1 cell line). The deformability of these cell types under varying channel width conditions was clearly assessed using this platform. The results demonstrated that tumor cells exhibited higher deformability compared to uroepithelial cells, with the EJ cell line exhibiting the greatest difference. Furthermore, the relationship between the malignancy, deformability, and uptake capability of bladder cells was explored through co-cultivation experiments with 2 μm particles. As the malignancy increased, the cells became more deformable and exhibited stronger phagocytic capability with particles. Subsequently, the heterogeneity of tumor cells was investigated by analyzing the deformability of phagocytic and non-phagocytic subpopulations within EJ cells. The developed microfluidic platform offers a promising high-throughput method to assess the biomechanical and phagocytic characteristics of cells, providing valuable insights into tumor cell biology, and potentially improving clinical status of urinary cytology examinations for bladder cancer.

Evaluation and Comparison of Stresses Between All-on-4 and All-on-6 Treatment Concepts With Three Different Prosthetic Materials in the Maxilla: A Finite Element Analysis Study.

This study aimed to evaluate the comparative analysis of stresses on and around implants and surrounding cortical bone using three different prosthetic materials in hybrid prosthesis using the all-on-4 technique and all-on-6 technique in the maxilla using finite element analysis (FEA). An in vitro FEA study was conducted where a three-dimensional (3D) model of an edentulous maxilla and four different models of the mandible were built using ANSYS software version 18 (Ansys, Inc., Canonsburg, Pennsylvania, United States). Group A comprised the all-on-4 technique where two vertical implants were placed in the lateral incisor area, and two tilted implants at 30o were placed in the second premolar area, whereas group B included the all-on-6 technique, where four vertical implants were placed in the central incisor and canine area, along with two tilted implants in second premolar area. Subsequently, prosthetic materials such as acrylic, porcelain fused to metal (PFM), and zirconia were studied. Four different opposing arch materials were made: natural teeth (A1 and B1), complete dentures (A2 and B2), implant-supported overdentures (A3 and B3), and hybrid prosthesis (A4 and B4). The von Mises stresses were recorded at the implant and cortical bone to summarize the effect of occlusal loads on the maxillary bone using the all-on-4 and all-on-6 techniques. In the all-on-4 technique, on evaluating stresses on implants, it was revealed that acrylic consistently demonstrated lower stress magnitudes in comparison to zirconia and PFM. The stress levels escalate from 38.72 MPa in model A1 to 72.43 MPa in model A4. Zirconia endured the most substantial stresses, ranging from 53.64 MPa (A1) to 84.87 MPa (A4). Similar results were obtained for the stresses on the cortical bone and for the all-on-6 technique. However, the stresses were lower in the all-on-6 technique than in the all-on-4 technique. The lowest stress values across all prosthetic materials were recorded when the maxillary arch was restored with acrylic teeth along with a titanium bar opposing natural dentition. The least stresses were noticed in the all-on-6 technique with acrylic prosthetic material opposing the natural dentition. As the all-on-6 treatment concept showed the most favorable biomechanical behavior, it can be considered a viable alternative for moderate atrophic maxillary rehabilitation.

Biomechanical investigation of positive reduction in the femoral neck fracture: a finite element analysis.

Gotfried positive reduction offers an alternative strategy for femoral neck fracture (FNF) when achieving anatomical reduction is challenging. However, the biomechanical consequences of positive reduction remain unclear. The purpose of this study was to investigate the biomechanical behavior of positive reduction across different Pauwels classification, providing a reference for quantifying positive reduction in clinical practice. Three-dimensional (3D) models of FNF were established and categorized according to the Pauwels classifications (Pauwels I, II, and III), each of them contained seven models with different reduction qualities, including an anatomical reduction model, two negative reduction models, and four positive reduction models, all of which were stabilized with dynamic hip screws (DHS) and cannulated screws (CS). We investigated the maximal von-Mises stress of internal fixation and proximal femoral, femoral fragment displacement, and maximal von-Mises strain at the proximal fragment fracture site when a 2100N load was applied to the femoral head. The maximum von-Mises stress on the internal fixators in each Pauwels group was lowest in the anatomical reduction model. In the Pauwels I group, positive reduction exceeding 3mm resulted in the maximum von-Mises stress on the internal fixators surpassing that of the negative reduction model. For the Pauwels II group, positive reduction beyond 2mm led to the maximum von-Mises stress on the internal fixators exceeding that of the negative reduction model. In the Pauwels III group, positive reduction beyond 1mm caused the maximum von-Mises stress on the internal fixators to be higher than that of the negative reduction model. The maximum von-Mises strain at the fracture site of proximal femur fragment increased with positive reduction. Varus displacement increased in positive reduction models as the Pauwels angle rose, potentially exacerbating rotation deformity in Pauwels III group. Excessive positive reduction may increase the risk of FNF failure after internal fixation. From a biomechanical stability perspective, positive reduction should be limited to 3mm or below in the Pauwels I group, restricted to not exceed 2mm in the Pauwels II group, and should not exceed 1mm in the Pauwels III group. Negative reduction should be avoided in all Pauwels groups.

Findings and perspectives of β-Ti alloys with biomedical applications: Exploring beyond biomechanical and biofunctional behaviour

Early implant failure and bone resorption may occur in load-bearing conditions as a result of stress shielding brought on by a mismatch in the bone-Ti-implant modulus. A review with a novel multidisciplinary perspective is proposed in this work, which considers recent developments of β-Titanium alloys and new trends in novel microstructures, processing techniques, properties of dense and porous substrates, as well as the relationship between all these aspects and performance in service, in terms of improved its biomechanical and bio-functional balance. In addition to highlighting several modern and historical uses for Ti alloys, this review covers many cutting-edge novel β-Ti alloys and uses that promise to exceed historical standards. Also, it deepens through several important properties of these alloys, including toxicity of alloying elements, phase stability, thermo-mechanical processing, heat treatment, surface, and stress-induced modifications. The stiffness, hardness, fatigue and wear resistance, corrosion behaviour, biocompatibility, and manufacturing and surface modification effects on these parameters are also emphasized. In-vitro and in-vivo assays have been added to highlight important aspects of bioactivity and antibacterial behaviour, and future significant research areas are suggested along with new techniques to ensure the successful clinical application of β-Ti alloys.

Comparing continuum and direct fiber models of soft tissues: An ocular biomechanics example reveals that continuum models may artificially disrupt the strains at both the tissue and fiber levels

Collagen fibers are the main load-bearing component of soft tissues but difficult to incorporate into models. Whilst simplified homogenization models suffice for some applications, a thorough mechanistic understanding requires accurate prediction of fiber behavior, including both detailed fiber-level strains and long-distance transmission. Our goal was to compare the performance of a continuum model of the optic nerve head (ONH) built using conventional techniques with a fiber model we recently introduced which explicitly incorporates the complex 3D organization and interaction of collagen fiber bundles [1]. To ensure a fair comparison, we constructed the continuum model with identical geometrical, structural, and boundary specifications as for the fiber model. We found that: 1) although both models accurately matched the intraocular pressure (IOP)-induced globally averaged displacement responses observed in experiments, they diverged significantly in their ability to replicate specific 3D tissue-level strain patterns. Notably, the fiber model faithfully replicated the experimentally observed depth-dependent variability of radial strain, the ring-like pattern of meridional strain, and the radial pattern of circumferential strain, whereas the continuum model failed to do so; 2) the continuum model disrupted the strain transmission along each fiber, a feature captured well by the fiber model. These results demonstrate limitations of the conventional continuum models that rely on homogenization and affine deformation assumptions, which render them incapable of capturing some complex tissue-level and fiber-level deformations. Our results show that the strengths of explicit fiber modeling help capture intricate ONH biomechanics. They potentially also help modeling other fibrous tissues. Statement of SignificanceUnderstanding the mechanics of fibrous tissues is crucial for advancing knowledge of various diseases. This study uses the ONH as a test case to compare conventional continuum models with fiber models that explicitly account for the complex fiber structure. We found that the fiber model captured better the biomechanical behaviors at both the tissue level and the fiber level. The insights gained from this study demonstrate the significant potential of fiber models to advance our understanding of not only glaucoma pathophysiology but also other conditions involving fibrous soft tissues. This can contribute to the development of therapeutic strategies across a wide range of applications.

The Effect of Different Separated File Retrieval Strategies on the Biomechanical Behavior of a Mandibular Molar: A Finite Element Analysis Study

IntroductionThis study evaluated the effects of retrieval strategies of separated nickel-titanium files on the biomechanical behavior of endodontically treated teeth by finite element analysis. MethodsSix FE models were created: intact tooth; simulated a scenario where the apical 3 mm of a nickel-titanium file is separated and retained; TD, simulated application of a trephine drill to expose 1 mm of the separated file; simulated troughing of 180° at the inner wall of root canal for an extra 1 mm of the separated file beyond the staging platform; simulated circumferential ultrasonic troughing done for an extra 1 mm after the TD; and PM, simulated iatrogenic perforation sealed using MTA. Occlusal loading followed the occlusal fingerprint of the tooth before maximum von Mises stresses, maximum principal stresses, safety factor, and number of cycles till failure were determined. The cervical region of the teeth and mid-root sections including the separated file was chosen as the areas of interest for further analysis. ResultsIntact tooth recorded the highest number of cycles till failure and safety factor. Other models showed a narrow range of variation in all aspects with the PM recording the lowest number of cycles till failure. The highest von Mises stress was recorded at the mesiobuccal line angle of the PM near its cervical margin, while the lowest was found at the intact tooth. ConclusionUnder the limitation of this study, various file retrieval strategies removing the surrounding root dentin within the amounts of general guidelines do not affect the biomechanical behavior of the tooth.

Nonlinear biomechanical behaviour of extracranial carotid artery aneurysms in the framework of Windkessel effect via FSI technique

Extracranial carotid artery aneurysms (ECCA) lead to rupture and neurologic symptoms from embolisation, with potentially fatal outcomes. Investigating the biomechanical behaviour of EECA with blood flow dynamics is crucial for identifying regions more susceptible to rupture. A coupled three-dimensional (3D) Windkessel-framework and hyperelastic fluid-structure interaction (FSI) analysis of ECCAs with patient-specific geometries, was developed in this paper with a particular focus on hemodynamic parameters and the arterial wall's biomechanical response. The blood flow has been modelled as non-Newtonian, pulsatile, and turbulent. The biomechanical characteristics of the aneurysm and artery are characterised employing a 5-parameter Mooney-Rivlin hyperelasticity model. The Windkessel effect is also considered to efficiently simulate pressure profile of the outlets and to capture the dynamic changes over the cardiac cycle. The study found the aneurysm carotid artery exhibited the high levels of pressure, wall shear stress (WSS), oscillatory shear index (OSI), and relative residence time (RRT) compared to the healthy one. The deformation of the arterial wall and the corresponding von Mises (VM) stress were found significantly increased in aneurysm cases, in comparison to that of no aneurysm cases, which strongly correlated with the hemodynamic characteristics of the blood flow and the geometric features of the aneurysms. This escalation would intensify the risk of aneurysm wall rupture. These findings have critical implications for enhancing treatment strategies for patients with extracranial aneurysms.

Biomechanical behaviour of tilted abutment after fixed partial denture restoration of CAD/CAM materials

BackgroundFailure to restore missing teeth in time can easily lead to the mesial tilting of the distal abutment teeth. However, a fixed partial denture (FPD) can improve stress conduction and distribution and prevent periodontal injuries. In these more complex cases, it is necessary to consider various factors comprehensively to improve conventional treatment planning and achieve better results.MethodsWe selected a patient with a missing first molar and a mesial inclination of the second molar, leaving inadequate space or bone mass for implant denture restoration, necessitating an FPD for restoration. Three-dimensional finite element analysis (3D-FEA) combined with photoelastic analysis were used to explore how the inclination angle (0 ‒ 30°) and different dental restoration materials (zirconia, lithium disilicate, polymer-infiltrated ceramic network, and resin composite) affect the biomechanical behaviour of FPD‒abutments‒periodontal tissue complex.ResultsThe stress was easily concentrated in the FPD connectors, enamel shoulder collar, periapical area, and root bifurcation. The stress on FPD and the periodontal ligament (PDL) of the second premolar increased with an increase in the elastic modulus of FPD, with an opposite trend in the abutments, the alveolar bone, and the PDL of the second molar. The stress on the FPD and alveolar bone increased with increased inclination angle of the distal abutment. The stress on two abutments and their PDL were positively correlated with the inclination angle in two stages; however, when the inclination angle > 12°, the second premolar and its PDL showed a negative correlation.ConclusionsFPDs can be used for restoration within 24° of distal abutment inclination, but protecting the abutments (< 12° especially) and the periodontal tissue (> 12° especially) must be taken seriously. For this purpose, an FPD material with higher strength is recommended.

Biomechanical analysis of cadaveric wrists before and after MOTEC wrist arthroplasty using a hexapod robot.

This study compares wrist motion, biomechanical behaviour and radiographic parameters before and after total wrist arthroplasty using a fourth-generation spherical articulation prosthesis. A total of 10 cadaveric specimens were assessed using a hexapod Stewart platform robot. After arthroplasty, there were significant increases in both stiffness and phase angle of wrist motion across all planes of motion assessed. In three specimens, a sudden increase in moment was observed on load/displacement curves. Radiographically, carpal height increased by 14%, and the centre of rotation was displaced 11.1 mm proximally, 4.6 mm dorsally and 3.9 mm radially. This stretched the musculotendinous units, tightening the joint, while increasing the moment arm of the wrist flexors and decreasing the moment arm of the extensors, potentially important in the development of postoperative flexion contractures. Possible alterations in technique and/or implant design are considered to assist surgeons in achieving optimal clinical and survivorship outcomes.

The modulation of lung cancer cell motility by Calponin 3 is achieved through its ability to sense and respond to changes in substrate stiffness.

The influence of extracellular matrix (ECM) stiffness on cell behavior is a well-established phenomenon. Tumor development is associated with the stiffening of the ECM. However, the understanding of the role of biomechanical behavior and mechanotransduction pathways in the oncogenesis of tumor cells remains limited. In this study, we constructed in vitro models using Polydimethylsiloxane substrates to create soft and stiff substrates. We then evaluated the migration of lung cancer cells A549 using video-microscopy and transwell assays. The mechanical properties were assessed through the utilization of atomic force microscopy, Optical Magnetic Twisting Cytometry, and traction force analysis. Additionally, the expression of Calponin 3 (CNN3) was evaluated using reverse transcription‑quantitative PCR and immunofluorescence techniques. Our observations indicate that the presence of a stiff substrate enhances A549 motility, as evidenced by increased stiffness and traction force in A549 cells on the stiff substrate. Furthermore, we observed a decrease in CNN3 expression in A549 cells on the stiff substrate. Notably, when CNN3 was overexpressed, it effectively inhibited the migration and invasion of A549 cells on the stiff substrate. The results of our study provide novel perspectives on the mechanisms underlying cancer cell migration in response to substrate mechanical properties.

Influence of Connector Design on Displacement and Micromotion in Tooth-Implant Fixed Partial Dentures Using Different Lengths and Diameters: A Three-Dimensional Finite Element Study.

The literature presents insufficient data evaluating the displacement and micromotion effects resulting from the combined use of tooth-implant connections in fixed partial dentures. Analyzing the biomechanical behavior of tooth-implant fixed partial denture (FPD) prothesis is vital for achieving an optimum design and successful clinical implementation. The objective of this study was to determine the relative significance of connector design on the displacement and micromotion of tooth-implant-supported fixed dental prostheses under occlusal vertical loading. A unilateral Kennedy class I mandibular model was created using a 3D reconstruction from CT scan data. Eight simulated designs of tooth-implant fixed partial dentures (FPDs) were split into two groups: Group A with rigid connectors and Group B with non-rigid connectors. The models were subjected to a uniform vertical load of 100 N. Displacement, strain, and stress were computed using finite element analysis. The materials were defined as isotropic, homogeneous, and exhibiting linear elastic properties. This study focused on assessing the maximum displacement in various components, including the bridge, mandible, dentin, cementum, periodontal ligament (PDL), and implant. Displacement values were predominantly higher in Group B (non-rigid) compared to Group A (rigid) in all measured components of the tooth-implant FPDs. Accordingly, a statistically significant difference was observed between the two groups at the FPD bridge (p value = 0.021 *), mandible (p value = 0.021 *), dentin (p value = 0.043 *), cementum (p value = 0.043 *), and PDL (p value = 0.043 *). Meanwhile, there was an insignificant increase in displacement values recorded in the distal implant (p value = 0.083). This study highlighted the importance of connector design in the overall stability and performance of the prosthesis. Notably, the 4.7 mm × 10 mm implant in Group B showed a displacement nearly 92 times higher than its rigid counterpart in Group A. Overall, the 5.7 mm × 10 mm combination of implant length and diameter showcased the best performance in both groups. The findings demonstrate that wider implants with a proportional length offer greater resistance to displacement forces. In addition, the use of rigid connection design provides superior biomechanical performance in tooth-implant fixed partial dentures and reduces the risk of micromotion with its associated complications such as ligament overstretching and implant overload, achieving predictable prognosis and enhancing the stability of the protheses.

Bioinspired Design of 3D-Printed Cellular Metamaterial Prosthetic Liners for Enhanced Comfort and Stability.

Traditional prosthetic liners are often limited in customization due to constraints in manufacturing processes and materials. Typically made from non-compressible elastomers, these liners can cause discomfort through uneven contact pressures and inadequate adaptation to the complex shape of the residual limb. This study explores the development of bioinspired cellular metamaterial prosthetic liners, designed using additive manufacturing techniques to improve comfort by reducing contact pressure and redistributing deformation at the limb-prosthesis interface. The gyroid unit cell was selected due to its favorable isotropic properties, ease of manufacturing, and ability to distribute loads efficiently. Following the initial unit cell identification analysis, the results from the uniaxial compression test on the metamaterial cellular samples were used to develop a multilinear material model, approximating the response of the metamaterial structure. Finite Element Analysis (FEA) using a previously developed generic limb-liner-socket model was employed to simulate and compare the biomechanical behavior of these novel liners against conventional silicone liners, focusing on key parameters such as peak contact pressure and liner deformation during donning, heel strike, and the push-off phase of the gait cycle. The results showed that while silicone liners provide good overall contact pressure reduction, cellular liners offer superior customization and performance optimization. The soft cellular liner significantly reduced peak contact pressure during donning compared to silicone liners but exhibited higher deformation, making it more suitable for sedentary individuals. In contrast, medium and hard cellular liners outperformed silicone liners for active individuals by reducing both contact pressure and deformation during dynamic gait phases, thereby enhancing stability. Specifically, a medium-density liner (10% infill) balanced contact pressure reduction with low deformation, offering a balance of comfort and stability. The hard cellular liner, ideal for high-impact activities, provided superior shape retention and support with lower liner deformation and comparable contact pressures to silicone liners. The results show that customizable stiffness in cellular metamaterial liners enables personalized design to address individual needs, whether focusing on comfort, stability, or both. These findings suggest that 3D-printed metamaterial liners could be a promising alternative to traditional prosthetic materials, warranting further research and clinical validation.

Semi-automated finite element analyses of surgically treated acetabular fractures to investigate the biomechanical behaviour of patient-specific compared to conventional implants

BackgroundIn acetabular fracture surgery, understanding the biomechanical behaviour of fractures and implants is beneficial for clinical decision-making about implant selection and postoperative (early) weightbearing protocols. This study outlines a novel approach for creating finite element models (FEA) from actual clinical cases. Our objectives were to (1) create a detailed semi-automatic three-dimensional FEA of a patient with a transverse posterior wall acetabular fracture and (2) biomechanically compare patient-specific implants with manually bent off-the-shelf implants.MethodsA computational study was performed in which we developed three finite element models. The models were derived from clinical imaging data of a 20-year-old male with a transverse posterior wall acetabular fracture treated with a patient-specific implant. This implant was designed to fit the patient's anatomy and fracture configuration, allowing for optimal placement and predetermined screw trajectories. The three FEA models included an intact hemipelvis for baseline comparison, one with a fracture fixated with a patient-specific implant, and another with a conventional implant. Two loading conditions were investigated: standing up and peak walking forces. Von Mises stress and displacement patterns in bone, implants and screws were analysed to assess the biomechanical behaviour of fracture fixation with either a patient-specific versus a conventional implant.ResultsThe finite element models demonstrated that for a transverse posterior wall type fracture, a patient-specific implant resulted in lower peak stresses in the bone (30 MPa and 56 MPa) in standing-up and peak walking scenario, respectively, compared to the conventional implant model (46 MPa and 90 MPa). The results suggested that patient-specific implant could safely withstand standing-up and walking after surgery, with maximum von Mises stresses in the implant of 156 MPa and 371 MPa, respectively. The results from the conventional implant indicate a likelihood of implant failure, with von Mises stresses in the implant (499 MPa and 1000 MPa) exceeding the yield stress of stainless steel.ConclusionThis study presents a workflow for conducting finite element analysis of real clinical cases in acetabular fracture surgery. This concept of personalized biomechanical fracture and implant assessment can eventually be applied in clinical settings to guide implant selection, compare conventional implants with innovative patient-specific ones, optimizing implant designs (including shape, size, materials, screw positions), and determine whether immediate full weight-bearing can be safely permitted.

Characterization of Limbus Biomechanical Properties Using Optical Coherence Elastography.

The elasticity of the limbus is crucial for ocular health, yet it remains inadequately explored. This study employs acoustic radiation force optical coherence elastography (ARF-OCE) to evaluate the biomechanical properties of the limbus under varying intraocular pressures. The method was validated using a heterogeneous phantom and subsequently applied to ex vivo porcine limbus samples. Elastic wave velocity at specific locations within the limbus was calculated, and the corresponding Young's modulus values were obtained. Spatial elasticity distribution maps were generated by correlating Young's modulus values with their respective locations in the two-dimensional structural images. The results indicate that ARF-OCE enhances the understanding of limbus biomechanical behavior and holds potential for diagnosing regional variations caused by ocular diseases.

Superior Measurement Accuracy of Digital Thickness Gauge Versus Digital Vernier Caliper in Determining Venous Tissue Thickness.

Background In determining mechanical characteristics, the accuracy of the thickness of the specimens can influence the biomechanical behavior, especially in the case of human tissues, where there is an important variability. This study aims to compare the accuracy of two routine measuring instruments, i.e., the digital vernier caliper and the digital thickness gauge, when measuring the thickness of venous specimens multiple times. Methodology In this study, we used 12 tubular vena cava specimens obtained from common breed pigs aged 18-24 weeks at the time of sacrifice from a local slaughterhouse. The measurements were performed using a digital vernier caliper (Multicomp PRO MP012475) for the first four protocols and a digital thickness gauge (Mitutoyo 547-500S) for the fifth protocol. In the first protocol, three measurements were taken on the same side, and their average was recorded as the sample thickness. The second protocol involved taking measurements on two opposite sides, and the average of these measurements was recorded as the sample thickness. In the third protocol, the thickness of each side was measured at its midpoint, and the average of the four measurements was recorded as the sample thickness. In the last protocol using a digital vernier caliper, the thickness of the vernier specimens was calculated as the average of the measurements taken at each corner of the square sample. Finally, for the fifth protocol, three consecutive measurements were taken using the digital thickness gauge, and their average was recorded as the final thickness of the sample. Results In the first protocol, we observed lower values during the first measurement in comparison to the second (0.409 ± 0.063 vs. 0.536 ± 0.064, p < 0.0001) and the third (0.409 ± 0.063 vs. 0.528 ± 0.055, p = 0.0001). Moreover, with the second protocol, we observed lower values during the first two measurements in comparison to the third measurement (p = 0.0279 and p = 0.0054). Regarding protocols three and four, we recorded higher values for the second and third measurements than the first one, with higher values for the third measurement than the second one. In the fifth protocol, there were no significant statistical differences between the three consecutive measurements (p = 0.953, p = 0.742, and p = 0.897). Further, we examined the variations in sample thickness determined using each of the protocols proposed for the digital vernier caliper, as well as the values obtained with the digital thickness gauge protocol. As a result, during the first and second measurements, we observed lower thickness values for the venous wall samples using the first four protocols compared to the fifth protocol (for all p < 0.05). However, no differences were noted between the five protocols during the third measurement. Conclusions The digital thickness gauge Mitutoyo 547-500S provided superior accuracy with no difference between three successive measurements of venous wall thickness, regardless of the examiner's experience. Accurately determining the thickness of venous specimens is crucial for calculating the tissue's biomechanical properties.