Predictive Models with Patient Specific Material Properties for the Biomechanical Behavior of Ascending Thoracic Aneurysms

International audienceThe aim of this study is to identify the patient-specific material properties of ascending thoracic aortic aneurysms (ATAA) using preoperative dynamic gated Computed Tomography (CT) scans. The identification is based on the simultaneous minimization of two cost functions, which define the difference between model predictions and gated CT measurements of the aneurysm volume at respectively systole and cardiac mid-cycle. The method is applied on 5 patients who underwent surgical repair of their ATAA at the University Hospital Center of St. Etienne. For these patients, the aneurysms were collected and tested mechanically using an in vitro bench. For the sake of validation, the mechanical properties found using the in vivo approach and the in vitro bench were compared. We eventually performed finite-element stress analyses based on each set of material properties. Rupture risk indexes were estimated and compared, 2 showing promising results of the patient-specific identification method based on gated CT

Biaxial rupture properties of ascending thoracic aortic aneurysms

International audienceAlthough hundreds of samples obtained from ascending thoracic aortic aneurysms (ATAA) of patients undergoing elective surgical repair have already been characterized biomechanically, their rupture properties were always derived from uniaxial tensile tests. Due to their bulge shape, ATAAs are stretched biaxially in vivo. In order to understand the biaxial rupture of ATAAs, our group developed a novel methodology based on bulge inflation and full-field optical measurements. The objective of the current paper is threefold. Firstly, we will review the failure properties (maximum stress, maximum stretch) obtained by bulge inflation testing on a cohort of 31 patients and compare them with failure properties obtained by uniaxial tension in a previously published study. Secondly, we will investigate the relationship between the failure properties and the age of patients, showing that patients below 55 years of age display significantly higher strength. Thirdly, we will define a rupture risk based on the extensibility of the tissue and we will show that this rupture risk is strongly correlated with the physiological elastic modulus of the tissue independently of the age, ATAA diameter or the aortic valve phenotype of the patient

Mechanical characterization of aortic valve tissues using an inverse analysis approach

International audienceThe use of numerical simulation to investigate heart and valvular mechanics is becoming increasingly popular. In particular, finite element analysis is often used to support the operation planning procedure as well as the design of new prostheses with mechanical properties as close as possible to those of natural tissues and an even better biocompatibility. With one of the highest prevalence of cardiovascular degenerative diseases [1], aortic valves (AV) have been widely studied during the last decades.The elastic [2] and time-dependent [3] behaviors of the AV leaflets under physiological biaxial loading states have been previously investigated in the literature over a wide range of loading conditions.. As most soft tissues, AV has an oriented network of collagen fibers embedded in an elastin matrix, which is responsible for their hyperelastic and anisotropic behaviors. Accordingly, non-linear transverse isotropic constitutive equations are often used assuming a macroscopically-identifiable preferred fiber direction.In this study a new method is proposed in order to estimate relevant material and structural properties of AV while reducing at the same time the number of complex and time-consuming experiments. An inverse analysis procedure based on the finite element computation of planar biaxial tensile tests was used to set-up a reduced protocol. This protocol was then experimentally reproduced to identify real material parameters. The obtained material parameters will be later used to model heart valve tissues

Climate change and viability of fruit tree orchards in arid area

The Mediterranean region is facing temperature increases due to climate change. More warm conditions across the fruit and nut growing regions are expected to have a great and negative impact in Tunisian arid regions. Chilling trends among the agricultural production areas and their incidence on flowering and fruiting of typical fruit species were investigated. The results showed important declines in winter chill accumulation over the main arid production areas. This lack of chill jeopardizing the flowering and fruiting of fruit species. However, fruit species and cultivars within each fruit species expressed different flowering and fruiting behaviors to warm climate depending on their chilling and heat requirements. Consequently, thermal requirements are a key factor for sustainable fruit trees’ orchards and to select suitable cultivation area. Adoption of appropriate genetic resources could be used to mitigate the harmful effect of global warming in arid regions

Postirradiation Osteosarcoma of the Maxilla: A Case Report and Current Review of Literature

Background. Radiation-induced sarcomas are well-known potential late sequelae of radiation therapy. They are of rare occurrence in jaw bones and are even rarer in the maxilla. Case report. We report a case of radiation-induced osteosarcoma involving the maxilla in a patient treated with radiotherapy for nasopharyngeal carcinoma 14 years ago. Despite neoadjuvant chemotherapy, surgical treatment could not be performed, and the patient received palliative chemotherapy. Conclusions. Radiation-induced osteosarcomas are aggressive and often elude early detection and timely intervention, rapidly leading to early demise of afflicted patients. Long-term patient follow-up and a high index of suspicion are crucial for timely intervention

A simple and effective 1D-element discrete-based method for computational bone remodeling

This is an Accepted Manuscript of an article published by Taylor & Francis Group in Computer Methods in Biomechanics and Biomedical Engineering on 2022, available online at: http://www.tandfonline.com/10.1080/10255842.2021.1943370.In-silico models applied to bone remodeling are widely used to investigate bone mechanics, bone diseases, bone-implant interactions, and also the effect of treatments of bone pathologies. This paper proposes a new methodology to solve the bone remodeling problem using one-dimensional (1D) elements to discretize trabecular structures more efficiently for 2D and 3D domains. An Euler integration scheme is coupled with the momentum equations to obtain the evolution of material density at each step. For the simulations, the equations were solved by using the finite element method, and two benchmark tests were solved varying mesh parameters. Proximal femur and calcaneus bone were selected as study cases given the vast research available on the topology of these bones, and compared with the anatomical features of trabecular bone reported in the literature. The presented methodology has proven to be efficient in optimizing topologies of lattice structures; It can predict the trend of formation patterns of the main trabecular groups from two different cancellous bones (femur and calcaneus) using domains set up by discrete elements as a starting point. Preliminary results confirm that the proposed approach is suitable and useful in bone remodeling problems leading to a considerable computational cost reduction. Characteristics similar to those encountered in topological optimization (TO) algorithms were identified in the benchmark tests as well, showing the viability of the proposed approach in other applications such as bio-inspired design.Peer ReviewedPostprint (author's final draft

Inverse identification of local stiffness across ascending thoracic aortic aneurysms

International audienceAortic dissection is the most common catastrophe of the thoracic aorta, with a very high rate of mortality. Type A dissection is often associated with an ascending thoracic aortic aneurysm (ATAA). However, it is widely acknowledged that the risk of type A dissection cannot be reliably predicted simply by measuring the ATAA diameter and there is a pressing need for more reliable risk predictors. It was previously shown that there is a signicant correlation between a rupture criterion based on the ultimate stretch of the ATAA and the local membrane sti-ness of the aorta. Therefore, reconstructing regional variations of the membrane stiness across the aorta appears highly important. In this paper, we present a novel noninvasive inverse method to identify the patientspecic local membrane stiness of aortic walls based on preoperative gated CT scans. Using these scans, a structural mesh is dened across the aorta with a set of nodes attached to the same material points at dierent time steps throughout the cardiac cycle. For each node, time variations of the position are analyzed using Fourier series, permitting the reconstruction of the local strain distribution (fundamental term). Relating these strains to tensions with the membrane stiness, and writing the local equi-2 Solmaz Farzaneh et al. librium satised by the tensions, the local membrane stiness is nally derived at every position. The methodology is applied onto the ascending and descending aorta of three patients. Interestingly, the regional distribution of identied stiness properties appears heterogeneous across the ATAA. Averagely, the identied sti-ness is also compared with values obtained using other non-local methodologies. The results support the possible non-invasive prediction of stretch-based rupture criteria in clinical practice using local stiness reconstruction

Identifying Local Arterial Stiffness to Assess the Risk of Rupture of Ascending Thoracic Aortic Aneurysms

International audienc

Antioxidant activity of extract of <i style="">Rhus oxyacantha</i> root cortex

246-249In the present study, the root extract of Rhus oxyacantha contained 25.33 mg of catechin equivalent per mg of fresh wt and was found rich in proanthocyanidins compared to vine shoot, grape pips and leaves. The chromatographic analysis of the extract suggested the presence of (+) catechin, (-) epicatechin -3-O-gallate as well as proanthocyanidinic oligomers and polymers. Root cortex inhibited the ascorbic acid oxidation by dioxygen. It also prevented DDT-induced thymocytes death in a dose-dependent manner. The results suggested antioxidant property of root extract of Rhus oxyacantha which could be ascribed to its free radical scavenging nature