17 results
Filters
Settings
Now showing1 - 10 of 17
- Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Gradient orientation governs mechanical and regenerative outcomes in functionally graded bone scaffolds: a coupled finite element–agent-based modelling studyCritical-sized bone defects remain a major clinical challenge, requiring scaffolds that combine mechanical stability with regenerative capacity. Functionally graded scaffolds offer a promising strategy by spatially varying porosity to optimise load transfer and tissue ingrowth. Here, we apply an established coupled poroelastic finite element–agent-based modelling (FEA–ABM) framework as a comparative platform to evaluate six cylindrical scaffold configurations modelled using Ti–6Al–4V material properties: two opposing axial-gradient designs, two opposing radial-gradient designs, and their corresponding uniform controls under physiologically representative loading. Poroelastic finite element analysis was used to compute local shear strain and fluid velocity, which regulated progenitor differentiation, proliferation, apoptosis, and migration in the agent-based model. Simulations representing 150 days of healing showed that axial gradients with larger pores at the host bone interface produced the greatest bone ingrowth, reaching approximately 77% pore occupancy compared with 69% in the uniform axial scaffold and 60% in the opposite axial gradient. In contrast, radial gradients did not substantially alter overall bone regeneration compared with the uniform radial scaffold, but the design with denser peripheral struts markedly improved mechanical performance, reducing volume-weighted P99 von Mises stress to approximately 41 MPa compared with about 57-71 MPa in the radial uniform and opposite radial-gradient designs. These findings reveal a design trade-off between regenerative capacity and structural competence, suggesting that gradient orientation should be selected according to the mechanical and biological requirements of the target defect environment. By applying the FEA–ABM framework consistently across the investigated configurations, this study provides comparative evidence to inform the selection of pore-size-gradient designs according to the regenerative and mechanical requirements of the target defect.Publicationtype: Journal Article4 3 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Biomechanical evaluation of shape-optimized CAD/CAM magnesium plates for mandibular reconstruction(Elsevier, 2026-01); ; ; ; Magnesium CAD/CAM miniplates are a promising alternative to titanium plates for mandibular reconstruction. However, gas formation is an inherent part of the magnesium degradation process, and thus, the quantity of magnesium used in fixation scenarios should be limited. Previous studies described several strategies to limit material volume, such as plate thickness reduction and shape-optimization. In particular, shape-optimization has been described as a strategy to limit material volume while maintaining mechanical integrity. In consequence, the present study compared a shape-optimized CAD/CAM magnesium miniplate with standard CAD/CAM magnesium miniplates of varying thicknesses using a biomechanical finite element model. A single-segment mandibular reconstruction was chosen as the investigative scenario, evaluated under different biting tasks to assess the different plate shapes. The shape-optimized magnesium plate demonstrated similar primary fixation stability compared to standard CAD/CAM magnesium miniplates, despite having reduced plate material and surface area. Shape optimization could help minimize magnesium volume and surface area to mitigate the issue of gas formation during the degradation process in vivo while maintaining biomechanical performance comparable to common CAD/CAM miniplates.Publicationtype: Journal Article18 24 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Dynamic biaxial loading of vascular smooth muscle cell seeded tissue equivalents(Elsevier, 2024-09-01); ; ; An intricate reciprocal relationship exists between adherent synthetic cells and their extracellular matrix (ECM). These cells deposit, organize, and degrade the ECM, which in turn influences cell phenotype via responses that include sensitivity to changes in the mechanical state that arises from changes in external loading. Collagen-based tissue equivalents are commonly used as simple but revealing model systems to study cell–matrix interactions. Nevertheless, few quantitative studies report changes in the forces that the cells establish and maintain in such gels under dynamic loading. Moreover, most prior studies have been limited to uniaxial experiments despite many soft tissues, including arteries, experiencing multiaxial loading in vivo. To begin to close this gap, we use a custom biaxial bioreactor to subject collagen gels seeded with primary aortic smooth muscle cells to different biaxial loading conditions. These conditions include cyclic loading with different amplitudes as well as different mechanical constraints at the boundaries of a cruciform sample. Irrespective of loading amplitude and boundary condition, similar mean steady-state biaxial forces emerged across all tests. Additionally, stiffness-force relationships assessed via intermittent equibiaxial force–extension tests showed remarkable similarity for ranges of forces to which the cells adapted during periods of cyclic loading. Taken together, these findings are consistent with a load-mediated homeostatic response by vascular smooth muscle cells.Publicationtype: Journal Article7 52 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Strength and ductility loss of Magnesium-Gadolinium due to corrosion in physiological environment: Experiments and modeling(Elsevier, 2023-08-01); ; ; Luczak, MonikaWe propose a computational framework to study the effect of corrosion on the mechanical strength of magnesium (Mg) samples. Our work is motivated by the need to predict the residual strength of biomedical Mg implants after a given period of degradation in a physiological environment. To model corrosion, a mass-diffusion type model is used that accounts for localised corrosion using Weibull statistics. The overall mass loss is prescribed (e.g., based on experimental data). The mechanical behaviour of the Mg samples is modeled by a state-of-the-art Cazacu–Plunkett–Barlat plasticity model with a coupled damage model. This allowed us to study how Mg degradation in immersed samples reduces the mechanical strength over time. We performed a large number of in vitro corrosion experiments and mechanical tests to validate our computational framework. Our framework could predict both the experimentally observed loss of mechanical strength and the ductility due to corrosion for both tension and compression tests.Publicationtype: Journal ArticleScopus© Citations 2 42 104 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Patient-specific miniplates versus patient-specific reconstruction plate: a biomechanical comparison with 3D-printed plates in mandibular reconstruction(Elsevier, 2023-02-24); ; ; ; Background: Patient-specific 3D-printed miniplates for free flap fixation in mandibular reconstruction were recently associated with enhanced osseous union. Higher mechanical strains resulting from these plates are discussed as reasons, but biomechanical studies are missing. This study aims to examine, whether patient-specific 3D-printed miniplates provide an increased interosteotomy movement (IOM) and lower stiffness compared with reconstruction plates. Methods: Polyurethane (PU) mandible and fibula models (Synbone AG, Malans, Schweiz) were used to simulate mandibular reconstruction with a one segment fibula flap equivalent. Osteosynthesis was performed using either four patient-specific 3D-printed miniplates (3D-Mini) or one patient-specific 3D-printed reconstruction plate (3D-Recon). Mastication was simulated using cyclic dynamic loading with increasing loads until material failure or a maximum load of 1000 N. Continuous IOM recording was carried out using a 3D optical tracking system (ARAMIS, Carl Zeiss GOM Metrology, Braunschweig, Germany). Findings: The averaged stiffness at a load of 100–300 N load did not differ between the groups (p = 0.296). There was a faster 1.0 mm vertical displacement in the 3D-Mini group (26 376 ± 14 190 cycles versus 44 817 ± 30 430 cycles, p = 0.018). The IOM were higher with miniplate fixation in the distal gap (p = 0.040). In the mesial gap, there was no significant difference between the groups (p = 0.160). Interpretation: Fixation with patient-specific 3D-printed miniplates results in higher mechanical strains. Lower rates of pseudarthrosis, as seen in clinical studies, might be caused by this phenomenon. Surgeons should evaluate the primary use of 3D-printed miniplates in mandibular reconstruction due to advantages of intraoral plate removal alongside safe osteosynthesis.Publicationtype: Journal Article39 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , No pressure, no diamonds? - Static vs. dynamic compressive in-situ loading to evaluate human articular cartilage functionality by functional MRIBiomechanical Magnetic Resonance Imaging (MRI) of articular cartilage, i.e. its imaging under loading, is a promising diagnostic tool to assess the tissue's functionality in health and disease. This study aimed to assess the response to static and dynamic loading of histologically intact cartilage samples by functional MRI and pressure-controlled in-situ loading. To this end, 47 cartilage samples were obtained from the medial femoral condyles of total knee arthroplasties (from 24 patients), prepared to standard thickness, and placed in a standard knee joint in a pressure-controlled whole knee-joint compressive loading device. Cartilage samples' responses to static (i.e. constant), dynamic (i.e. alternating), and no loading, i.e. free-swelling conditions, were assessed before (δ ), and after 30 min (δ ) and 60 min (δ ) of loading using serial T1ρ maps acquired on a 3.0T clinical MRI scanner (Achieva, Philips). Alongside texture features, relative changes in T1ρ (Δ , Δ ) were determined for the upper and lower sample halves and the entire sample, analyzed using appropriate statistical tests, and referenced to histological (Mankin scoring) and biomechanical reference measures (tangent stiffness). Histological, biomechanical, and T1ρ sample characteristics at δ were relatively homogenous in all samples. In response to loading, relative increases in T1ρ were strong and significant after dynamic loading (Δ = 10.3 ± 17.0%, Δ = 21.6 ± 21.8%, p = 0.002), while relative increases in T1ρ after static loading and in controls were moderate and not significant. Generally, texture features did not demonstrate clear loading-related associations underlying the spatial relationships of T1ρ. When realizing the clinical translation, this in-situ study suggests that serial T1ρ mapping is best combined with dynamic loading to assess cartilage functionality in humans based on advanced MRI techniques.Publicationtype: Journal Article63 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Biomechanical comparison of titanium miniplates versus a variety of CAD/CAM plates in mandibular reconstructionBackground: Titanium plate fixation of free flaps in mandibular reconstruction involves complications such as osseous non-union or imaging artefacts. Interosteotomy movement (IOM) is known to affect bone healing. This study aimed to compare IOM and mechanical integrity of four different fixation systems in a mandible reconstruction model. Methods: Two polyurethane (PU) fibula segments were fixed in right-sided defects of PU mandibles. Laser-melted patient-specific titanium plates were fixed with non-locking-screws (Ti-NL) or locking-screws (Ti-L). The third group consisted of locking-screws for patient-specific polyetheretherketone (PEEK-L) plates. The last group used titanium miniplates and monocortical screw fixation (Ti-MP). All models were loaded unilaterally via cyclic dynamic loading with increasing loads to simulate mastication. IOM was registered using a 3D optical tracking system. Findings: PEEK-L showed highest vertical displacement (p = 0.010), lowest stiffness (p = 0.004) and highest IOM (p = 0.001). All specimen in PEEK-L demonstrated abnormal bending (n = 5) or plate fracture (n = 1). Vertical displacement or stiffness did not differ between any of Ti-MP, Ti-L and Ti-NL. IOM in Ti-MP was higher than in Ti-L and Ti-NL (p = 0.001). Interpretation: Mechanical integrity of all titanium plates complies with established standards. In this model, the screw system did not influence IOM. In the tested composition and shape, PEEK plates do not seem to guarantee sufficient mechanical integrity for a use in mandibular reconstruction. Thus modifications are needed. Future clinical studies are needed to clarify optimal IOM after mandible reconstruction.Publicationtype: Journal Article102 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Articulation of an alumina-zirconia composite ceramic against living cartilage – An in vitro wear testBackground: There is interest in minimally invasive solutions that reduce osteoarthritic symptoms and restore joint mobility in the early stages of cartilage degeneration. The aim of the present study was to evaluate an alumina-zirconia composite (AZC) as a counterface for articulation against live cartilage explants in comparison to the clinically relevant cobalt-chromium (CoCrMo) alloy. Methods: A four-station bioreactor designed to articulate against living tissue in an incubator was used for testing. Twelve 32 mm AZC and twelve 32 mm CoCrMo femoral heads with equal surface roughness made up both test groups. Each head articulated against a cartilage disk harvested from stifle joints of 24-week old steers. Test samples and free-swelling control cartilage samples were cultured in Mini ITS medium. Testing was conducted 3 h daily over 10 days applying a contact load of approximately 2 MPa. PG/GAG and hydroxyproline were analyzed using biochemical assays. Additionally, chondrocyte survival and Mankin score analyses were performed on histological slides. Results: Cells stayed alive during the course of the experiment, with cell survival values close to 80% at test completion in the superficial zone. There was no significant difference between AZC and free-swelling control tissue. However, cell count values were inferior for CoCrMo (p = 0.003). Tested tissue suffered mostly structural abnormalities. The PG/GAG content in medium was not different between CoCrMo and AZC (p = 0.315); however, the hydroxyproline release into medium was nearly 30% higher for CoCrMo (p = 0.024). Conclusion: Based on average values, AZC induces less cell and tissue damage than CoCrMo. However, only the hydroxyproline measurements reached statistical significance, partially due to substantial scatter within both groups.Publicationtype: Journal Article87 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Patient specific glass fiber reinforced composite versus titanium plate: A comparative biomechanical analysis under cyclic dynamic loadingFree flap fixation with patient specific titanium (TI) plates is commonly performed after oncologic mandible resection, but plate exposure, osseous nonunion and imaging artefacts are associated complications. The aim of this study was to analyze interfragmentary movements and fatigue behaviour of patient specific titanium plates in comparison to a novel glass fiber reinforced composite (GFRC) plate in vitro.Publicationtype: Journal Article341 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Test method for mechanical properties of implantable catheters according to DIN 10555-3To enable causal analysis of port catheter failure, this study aimed to develop an experimental setup for uniaxial tensile tests that addresses the specific requirements of highly elastic medical catheters; and to quantify parameters of the catheters’ mechanical competence with respect to effects of artificial aging. Segments of 6F-polyurethane catheters were tested in their native status, after chemical and after mechanical aging. Tension experiments were performed with a rate of 220 mm/min until catheter failure. Material behavior was analyzed based on load cell measurements of the universal test system and an additional optical distance registration. The Young's modulus, the ultimate stress and the ultimate strain were determined. Chemical aging significantly decreased Young's modulus (84%; p = 0.001) and ultimate stress (83%; p < 0.001), whereas mechanical aged samples demonstrated similar results for the Young's modulus (p = 0.772) and a non-significant rise of ultimate stress (13%; p = 0.128). Ultimate strain did not differ significantly regardless of the pretreatment. The results proof reliability, reproducibility and sensitivity to quantify artificial aging induced variations and also promise to detect deviations in material features caused by long-term clinical usage of catheters.Publicationtype: Journal Article187