FE analysis of aortoiliac bifurcation

This action is realized by the project NEXLIZ - CZ.1.07/2.3.00/30.0038, which is co-financed by the European social fund and the state budget of the Czech republic

FINITE ELEMENT ANALYSIS OF AORTAL BIFURCATION

Arterial bifurcations loaded by internal pressure represent significant stress concentrators. Increased mechanical stress inside arterial wall probably accelerates pathogenic processes at these places. Stress concentration factor (SCF) depends mainly on geometry, loading and material. This work presents a map of SCFs calculated by FEM at aortic bifurcation (AB) loaded by static internal pressure. Influence of geometry (aortic diameter, wall thickness, bifurcation angle, "non-planarity" angle and radius of apex), material properties and internal pressure were evaluated statistically by regression of FEM results. Two variants of materials were used (linear Hook and hyper elastic Ogden). Viscoelastic behaviour, anisotropy and prestrain were neglected. Results indicate that the highest Mises stress appears in the inner side of AB apex and that the SCF is negatively correlated with bifurcation angle and with internal pressure. The SCF varies from 4,5 to 7,5 (Hook) and from 7 to 21 (Ogden)

DEVELOPMENT OF NEW TECHNIQUE FOR ACCURATE WEAR ANALYSIS OF EXPLANTED TOTAL HIP REPLACEMENTS

Wear is a fundamental problem in relation to the life-time of the hip joint implants, especially for the components of the ultra-high molecular weight polyethylene (UHMWPE). Therefore, the better understanding of the properties and capabilities of UHMWPE related to wear is crucial for the improvement of the implants' behavior. The purpose of this study is to present a new methodology for calculating volumetric wear of retrieved hip prostheses using a combination of novel co-ordinate measuring machine data and Matlab GUI program (Mathworks, Inc.). Method utilizes the unworn portion of the explanted acetabular cup to create or reconstruct the original unworn surface. From these unworn surfaces, it is possible to directly calculate volumetric wear and to graphically map the wear scar, i.e. the penetration of the femoral head into the acetabular cup

LAD models, trees and an analog of the fundamental theorem of arithmetic

International audienceMotivated by applications of Logical Analysis Data (LAD) in medical contexts, original discrete optimization problems are proposed. When a patient arrives with a presumption of a disease, he is submitted to a sequence of tests. From one patient to another, the tests allowing to detect the disease may vary. A subset of tests whose results detect the disease in a given part of the population is called a pattern, which has its own prevalence in the population. If there is only a limited number of tests that can be done, which ones must be selected in order to maximize the number of spotted patients ? Or, if each test has a cost, in which order the tests have to be done, in order to minimize the cost ? It is the kind of questions that are investigated in this paper. For various special cases, polynomial algorithms are proposed, especially when the hypergraph whose vertices are the tests and whose edges are the patterns is a tree graph. One of these questions involves a criterion which is not a number but a sequence of numbers. The objective is then to find the best sequence for the lexicographic order. To solve this question, a new product on finite sequences is defined, namely the maximum shuffle product, which maps two sequences to their shuffle that is maximal for the lexicographic order. Surprisingly, this product leads to a theorem similar to the fundamental theorem of arithmetic: every sequence can be written uniquely as the product of prime sequences, with the suitable definition of prime sequences

Grafting of magnetic particles with poly(2-isopropenyl-2-oxazoline)

Magnetic particles play an important role in modern biomedical applications including targeted drug delivery, local embolization of blood veins, hyperthermia etc. Therefore, the development of more effective systems with high biocompatibility is of interest for many researchers. Nevertheless, these magnetic systems have to meet certain criteria necessary for in vivo applications. We have considered key requirements desired from such materials, and we have prepared a promising system based on core-shell particles via surface-initiated atom transfer radical polymerization (ATRP). The finest grade of the carbonyl iron particles was used as a suitable core and the treatment of its surface in acidic environment ensured the presence of hydroxyl groups, which were further coupled with ethoxy groups of (3-Aminopropyl)triethoxysilane. After the functionalization, the immobilization of 2-Bromoisobutyryl bromide, which served as an initiator, was performed. Finally, the initiator-treated particles were grafted with poly(2-isopropenyl-2-oxazoline) (PIPOx) under ATRP conditions as the PIPOx has recently shown a great potential in biomedical applications. The cleaning and washing procedures ensured high purity of the product. The reaction conversion, molar mass and dispersity of PIPOx grafts were investigated using nuclear magnetic resonance and gel permeation chromatography, respectively. The presence of grafted PIPOx was confirmed using Fourier-transform infrared, and energy-dispersive X-ray spectroscopies. The grafted PIPOx layer had negligible effect on particle magnetization as revealed via vibration-sample magnetometry. Synthesized core-shell structures may find utilization as a promising material for local embolization or may serve as a drug delivery system due to the presence of PIPOx bearing the active sites allowing the drug bonding. © 2018 TANGER Ltd. All Rights Reserved.Grant Agency of the Czech Republic [17-24730S]; Internal Grant Agency of Tomas Bata University in Zlin [IGA/CPS/2017/004]; Ministry of Education, Youth and Sports of the Czech Republic - Program NPU I [LO1504]; [APVV-15-0545

Effects of Age and Loading Velocity on the Delamination Strength of the Human Aorta

Delamination strength is the mechanical property which plays a key role in the pathological process referred to as Arterial Dissection. This dissection, known especially for its occurrence in the thoracic aorta, is manifested by a separation of the layers of an artery wall, and may end with total rupture and internal haemorrhaging. Although its incidence is relatively rare, from 3 to 6 cases per 100 000 per year, it is a life-threating disease with a significant lethality [1-3]. The exact conditions under which the dissection is initiated, and as a crack propagates through the arterial wall, remain an open topic in computational as well as experimental mechanics. The aim of our study is to contribute to the deepening of our knowledge of Arterial Dissection, by collecting experimental data which is suitable for the purpose of showing how the delamination strength measured in the peeling experiments depends on age and anatomical location. In addition to the effects of age and location, our study also focuses on the effect of loading rate. The experimental branch of our research is complemented by a computational modelling of the delamination interface, in which we are looking for a numerical characterization of the material parameters describing discontinuity propagation. An XFEM model of the peeling experiment is built in Abaqus, which in our approach plays the role of the regression analysis, incorporating the cohesive zone (CZ) in order to model the delaminating arterial layers. The main objective is to obtain a detailed description of a set of constitutive parameters, which would be age- and location-specific. Our present data suggest that delamination strength strongly depends on age, and furthermore, the anatomical site also seems to be a significant factor. On the other hand, the loading velocity does not cause significant changes in results

Survival dimensionality reduction (SDR): development and clinical application of an innovative approach to detect epistasis in presence of right-censored data

Contains fulltext : 89126.pdf (publisher's version ) (Open Access)BACKGROUND: Epistasis is recognized as a fundamental part of the genetic architecture of individuals. Several computational approaches have been developed to model gene-gene interactions in case-control studies, however, none of them is suitable for time-dependent analysis. Herein we introduce the Survival Dimensionality Reduction (SDR) algorithm, a non-parametric method specifically designed to detect epistasis in lifetime datasets. RESULTS: The algorithm requires neither specification about the underlying survival distribution nor about the underlying interaction model and proved satisfactorily powerful to detect a set of causative genes in synthetic epistatic lifetime datasets with a limited number of samples and high degree of right-censorship (up to 70%). The SDR method was then applied to a series of 386 Dutch patients with active rheumatoid arthritis that were treated with anti-TNF biological agents. Among a set of 39 candidate genes, none of which showed a detectable marginal effect on anti-TNF responses, the SDR algorithm did find that the rs1801274 SNP in the Fc gamma RIIa gene and the rs10954213 SNP in the IRF5 gene non-linearly interact to predict clinical remission after anti-TNF biologicals. CONCLUSIONS: Simulation studies and application in a real-world setting support the capability of the SDR algorithm to model epistatic interactions in candidate-genes studies in presence of right-censored data. Availability: http://sourceforge.net/projects/sdrproject/

FE analysis of aortoiliac bifurcation

This action is realized by the project NEXLIZ - CZ.1.07/2.3.00/30.0038, which is co-financed by the European social fund and the state budget of the Czech republic