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Sökning: WFRF:(Gasser T)

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21.
  • Singh, T. P., et al. (författare)
  • Systematic review and meta-analysis of the association between intraluminal thrombus volume and abdominal aortic aneurysm rupture
  • 2019
  • Ingår i: Journal of Vascular Surgery. - : Mosby Inc.. - 0741-5214 .- 1097-6809. ; 70:6, s. 2065--2073.e10
  • Forskningsöversikt (refereegranskat)abstract
    • Background: Intraluminal thrombus (ILT) is present in most abdominal aortic aneurysms (AAAs), although its role in AAA progression is controversial. Methods: A literature search was performed to identify studies that investigated the association between ILT volume and AAA rupture. A study assessment tool was developed to assess the methodologic quality of included studies. A meta-analysis was conducted using an inverse variance-weighted random-effects model to compare the ILT volume in ruptured and asymptomatic intact AAAs. Leave-one-out sensitivity analyses were conducted to assess the robustness of the findings. A subanalysis was performed including studies in which patients with asymptomatic intact and ruptured AAAs were matched for aortic diameter. Interstudy heterogeneity was assessed using the I2 statistic. Results: Eight studies involving 672 patients were included in this systematic review. Meta-analysis of all studies found a greater ILT volume in patients with ruptured AAAs than in patients with asymptomatic intact AAAs (standardized mean difference, 0.56; 95% confidence interval, 0.17-0.96; P =.005; I2 = 79.8%). Sensitivity analyses suggested that the findings were robust; however, aortic diameter was significantly larger in ruptured than in asymptomatic intact AAAs (mean ± standard deviation, 78 ± 18 and 64 ± 15 mm, respectively; P <.001). In the subanalysis of studies that matched for diameter, no significant difference in ILT volume between groups was found (standardized mean difference, 0.03; 95% confidence interval, −0.27 to 0.33; P =.824; I2 = 0%). Conclusions: This meta-analysis suggests that ILT volume is greater in patients with ruptured AAAs than in patients with asymptomatic intact AAAs, although this is most likely due to the larger diameter of ruptured AAAs.
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25.
  • Ahlinder, Astrid (författare)
  • Degradable copolymers in additive manufacturing: controlled fabrication of pliable scaffolds
  • 2021
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • Inom vävnadsregenerering är produktionen av väldefinieradematriser med en porös arkitektur av nedbrytbara polymerer av stortintresse, dessa kan nu skapas genom additiva tillverkningsprocesser. Vidadditiv tillverkning krävs ett smalt munstycke för att skapa detaljrikastrukturer och detta ställer krav på att de reologiska egenskapernaanpassat. Lägre viskositet av smältan gör de lättare att använda, men enhög molmassa krävs för tillverka matriser där de mekaniska egenskapernakan bibehållas under tiden som krävs för vävnadsregenerering. Ytterligareen utmaning uppstår när nedbrytbara polymerer används i smältbaseradadditiva tillverkningsprocesser är att termisk nedbrytning ofta reducerarmolmassan redan under produktionsfasen. För att kunna användanedbrytbara polymerer av medicinsk kvalitet i smältbaserad additivtillverkning och samtidigt minimera den termiska nedbrytningen har, idenna avhandling, reologiska fingeravtryck av nedbrytbara syntetiskapolymerer med medicinsk kvalitet använts för att bestämmaprocessparametrar. Termisk nedbrytning beroende av processparamaterar har analyserats och minimeras i två smältbaserade additivatillverkningsprocesser.En additiv tillverkningsprocess var designad där nedbrytbarapolymerer av hög molmassa kunde användas utan termisk nedbrytning närprocessparametrar hade valts utifrån polymerens egenskaper. Kunskapenom användningen av dessa polymerer inom additiv tillverkning kundeappliceras på en sampolymer som utvecklats inom forskningsgruppen förmjukvävnad, poly(ε-kaprolakton-co-p-dioxanon) för att skapa böjbaramatriser. Genom att använda reologisk analys och polymerkarakteriseringerhölls processparametrar som möjliggjorde additiv tillverkning utantermisk nedbrytning. I tillägg till val av polymer och processparametrar såkan mekaniska egenskaper också styras av den strukturella designen.Poly(ε-kaprolakton) användes som modellmaterial för att reducerastyvheten med hjälp av designen, resultatet visade att det var möjligt medmer än en faktor 10 och mjuka böjbara matriser skapades.
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27.
  • Alloisio, Marta, et al. (författare)
  • Fracture of porcine aorta-Part 1 : symconCT fracture testing and DIC
  • 2023
  • Ingår i: Acta Biomaterialia. - : Elsevier BV. - 1742-7061 .- 1878-7568. ; 167, s. 147-157
  • Tidskriftsartikel (refereegranskat)abstract
    • Tissue failure and damage are inherent parts of vascular diseases and tightly linked to clinical events. Additionally, experimental set-ups designed to study classical engineering materials are suboptimal in the exploration of vessel wall fracture properties. The classical Compact Tension (CT) test was augmented to enable stable fracture propagation, resulting in the symmetry-constraint Compact Tension (symconCT) test, a suitable set-up for fracture testing of vascular tissue. The test was combined with Digital Image Correlation (DIC) to study tissue fracture in 45 porcine aorta specimens. Test specimens were loaded in axial and circumferential directions in a physiological solution at 37 & DEG;C. Loading the aortic vessel wall in the axial direction resulted in mode I tissue failure and a fracture path aligned with the circumferential vessel direction. Circumferential loading resulted in mode I-dominated failure with multiple deflections of the fracture path. The aorta ruptured at a principal Green-Lagrange strain of approximately 0.7, and strain rate peaks that develop ahead of the crack tip reached nearly 400 times the strain rate on average over the test specimen. It required approximately 70% more external work to fracture the aorta by circumferential than axial load; normalised with the fracture surface, similar energy levels are, however, observed. The symconCT test resulted in a stable fracture propagation, which, combined with DIC, provided a set-up for the in-depth analysis of vascular tissue failure. The high strain rates ahead of the crack tip indicate the significance of rate effects in the constitutive description of vascular tissue fracture.
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28.
  • Alloisio, Marta, et al. (författare)
  • Fracture of porcine aorta. Part 2: FEM modelling and inverse parameter identification
  • 2023
  • Ingår i: Acta Biomaterialia. - : Acta Materialia Inc. - 1742-7061 .- 1878-7568. ; 167, s. 158-170
  • Tidskriftsartikel (refereegranskat)abstract
    • The mechanics of vascular tissue, particularly its fracture properties, are crucial in the onset and progression of vascular diseases. Vascular tissue properties are complex, and the identification of fracture mechanical properties relies on robust and efficient numerical tools. In this study, we propose a parameter identification pipeline to extract tissue properties from force-displacement and digital image correlation (DIC) data. The data has been acquired by symconCT testing porcine aorta wall specimens. Vascular tissue is modelled as a non-linear viscoelastic isotropic solid, and an isotropic cohesive zone model describes tissue fracture. The model closely replicated the experimental observations and identified the fracture energies of 1.57±0.82 kJ m−2 and 0.96±0.34 kJ m−2 for rupturing the porcine aortic media along the circumferential and axial directions, respectively. The identified strength was always below 350 kPa, a value significantly lower than identified through classical protocols, such as simple tension, and sheds new light on the resilience of the aorta. Further refinements to the model, such as considering rate effects in the fracture process zone and tissue anisotropy, could have improved the simulation results. Statement of significance: This paper identified porcine aorta's biomechanical properties using data acquired through a previously developed experimental protocol, the symmetry-constraint compact tension test. An implicit finite element method model mimicked the test, and a two-step approach identified the material's elastic and fracture properties directly from force-displacement curves and digital image correlation-based strain measurements. Our findings show a lower strength of the abdominal aorta as compared to the literature, which may have significant implications for the clinical evaluation of the risk of aortic rupture.
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29.
  • Auer, M., et al. (författare)
  • Reconstruction and Finite Element Mesh Generation of Abdominal Aortic Aneurysms From Computerized Tomography Angiography Data With Minimal User Interactions
  • 2010
  • Ingår i: IEEE Transactions on Medical Imaging. - : Institute of Electrical and Electronics Engineers (IEEE). - 0278-0062 .- 1558-254X. ; 29:4, s. 1022-1028
  • Tidskriftsartikel (refereegranskat)abstract
    • Evaluating rupture risk of abdominal aortic aneurysms is critically important in reducing related mortality without unnecessarily increasing the rate of elective repair. According to the current clinical practice aneurysm rupture risk is (mainly) estimated from its maximum diameter and/or expansion rate; an approach motivated from statistics but known to fail often in individuals. In contrast, recent research demonstrated that patient specific biomechanical simulations can provide more reliable diagnostic parameters, however current structural model development is cumbersome and time consuming. This paper used 2D and 3D deformable models to reconstruct aneurysms from computerized tomography angiography data with minimal user interactions. In particular, formulations of frames and shells, as known from structural mechanics, were used to define deformable modes, which in turn allowed a direct mechanical interpretation of the applied set of reconstruction parameters. Likewise, a parallel finite element implementation of the models allows the segmentation of clinical cases on standard personal computers within a few minutes. The particular topology of the applied 3D deformable models supports a fast and simple hexahedral-dominated meshing of the arising generally polyhedral domain. The variability of the derived segmentations (luminal: 0.50(SD 0.19) mm; exterior 0.89(SD 0.45) mm) with respect to large variations in elastic properties of the deformable models was in the range of the differences between manual segmentations as performed by experts (luminal: 0.57(SD 0.24) mm; exterior: 0.77(SD 0.58) mm), and was particularly independent from the algorithm's initialization. The proposed interaction of deformable models and mesh generation defines finite element meshes suitable to perform accurate and efficient structural analysis of the aneurysm using mixed finite element formulations.
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30.
  • Biasetti, Jacopo, et al. (författare)
  • An Integrated Fluid-Chemical Model Toward Modeling the Formation of Intra-Luminal Thrombus in Abdominal Aortic Aneurysms
  • 2012
  • Ingår i: Frontiers in Physiology. - : Frontiers Media SA. - 1664-042X. ; 3:266
  • Tidskriftsartikel (refereegranskat)abstract
    • Abdominal Aortic Aneurysms (AAAs) are frequently characterized by the presence of an Intra-Luminal Thrombus (ILT) known to influence their evolution biochemically and biomechanically. The ILT progression mechanism is still unclear and little is known regarding the impact of the chemical species transported by blood flow on this mechanism. Chemical agonists and antagonists of platelets activation, aggregation, and adhesion and the proteins involved in the coagulation cascade (CC) may play an important role in ILT development. Starting from this assumption, the evolution of chemical species involved in the CC, their relation to coherent vortical structures (VSs) and their possible effect on ILT evolution have been studied. To this end a fluid-chemical model that simulates the CC through a series of convection-diffusion-reaction (CDR) equations has been developed. The model involves plasma-phase and surface-bound enzymes and zymogens, and includes both plasma-phase and membrane-phase reactions. Blood is modeled as a non-Newtonian incompressible fluid. VSs convect thrombin in the domain and lead to the high concentration observed in the distal portion of the AAA. This finding is in line with the clinical observations showing that the thickest ILT is usually seen in the distal AAA region. The proposed model, due to its ability to couple the fluid and chemical domains, provides an integrated mechanochemical picture that potentially could help unveil mechanisms of ILT formation and development.
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