Simulation du déploiement d'endoprothèses dans des anévrismes iliaques tortueux

National audienceLe traitement des anévrismes par voie endovasculaire avec pose d'une endoprothèse (EP) est une technique de choix face à la chirurgie ouverte conventionnelle, mais elle reste à fiabiliser. Dans cette étude, une simulation complète par éléments finis de la pose d'EP est proposée afin d'évaluer et comparer les performances mécaniques de cinq dispositifs du marché. Les résultats confirment l'importance de la flexibilité des EPs et offrent une avancée notable dans la simulation de la chirurgie endovasculaire

Finite Element Analysis of the Mechanical Performances of 8 Marketed Aortic Stent-Grafts

International audiencePurpose: To assess numerically the flexibility and mechanical stresses undergone by stents and fabric of currently manufactured stent-grafts. Methods: Eight marketed stent-graft limbs (Aorfix, Anaconda, Endurant, Excluder, Talent, Zenith Flex, Zenith LP, and Zenith Spiral-Z) were modeled using finite element analysis. A numerical benchmark combining bending up to 180° and pressurization at 150 mmHg of the stent-grafts was performed. Stent-graft flexibility, assessed by the calculation of the luminal reduction rate, maximal stresses in stents, and maximal strains in fabric were assessed. Results: The luminal reduction rate at 90° was ‹<20% except for the Talent stent-graft. The rate at 180° was higher for Z-stented models (Talent, Endurant, Zenith, and Zenith LP; range 39%-78%) than spiral (Aorfix, Excluder, and Zenith Spiral-Z) or circular-stented (Anaconda) devices (range 14%-26%). At 180°, maximal stress was higher for Z-stented stent-grafts (range 370-622 MPa) than spiral or circular-stented endografts (range 177-368 MPa). At 90° and 180°, strains in fabric were low and did not differ significantly among the polyester stent-grafts (range 0.5%-7%), while the expanded polytetrafluoroethylene fabric of the Excluder stent-graft underwent higher strains (range 11%-18%). Conclusion: Stent design strongly influences mechanical performances of aortic stentgrafts. Spiral and circular stents provide greater flexibility, as well as lower stress values than Z-stents, and thus better durability

Analyse des performances mécaniques des endoprothèses aortiques par simulation numérique : Application au traitement des anévrismes tortueux.

The aim of the endovascular repair (EVAR) of abdominal aortic aneurysm (AAA) is to set up a stent-graft (SG) within the aneurysm in order to avoid its rupture. This surgery is mini-invasive and can be used for patients who are ineligible for open surgery. However, complications mainly due to mechanical issues can occur during patient follow-up, such as endoleak or stenosis for example. A better knowledge of SG mechanical behaviour could be useful to improve SG design and durability which still prevents surgeons to use this treatment systematically. A new methodology to model multi-material SGs has been developed. Special attention has been paid to the mechanical characterization of stent and graft materials. SG numerical models have been qualitatively and quantitatively validated on a bending test by the means of tomographic acquisitions and image processing, showing their reliability. Mechanical performances of several marketed SGs have been assessed through various tests increasingly closer to the in vivo conditions undergone by the devices. SGs have been subjected to pure bending tests, then to tests combining bending and pressurisation. SG flexibility and components mechanical response have been compared and SGs have been ranked according to their performances. It has been shown that SG architecture has a significant influence on SG mechanical performances. Finally, SG deployment within two aneurysm models has been successfully simulated. The latter study highlighted other complications, like type I endoleak. This work has many promising perspectives, especially the development of a computer-aided surgery.Finite element analysis of the mechanical performances of aortic stent-grafts: application to the treatment of tortuous aneurysms.Le traitement endovasculaire (EVAR) de l'anévrisme de l'aorte abdominale (AAA) vise à mettre en place une endoprothèse (EP) au sein du sac anévrismal afin d'éviter sa rupture. Si cette chirurgie a l'avantage d'être mini-invasive et de pouvoir être utilisée pour des patients non éligibles à la chirurgie ouverte classique, il existe cependant plusieurs événements indésirables, pouvant apparaître au cours du suivi du patient. Mieux connaître le comportement mécanique des EPs permettrait ainsi d'améliorer leur conception et leur durabilité, principaux verrous au recours systématique à l'EVAR. Ainsi, une méthode de modélisation numérique multi matériaux des EPs a été développée. Les modèles numériques d'EPs ont été validés à partir d'une analyse d'images 3D obtenues par tomographie aux rayons X, montrant ainsi leur fiabilité. Les performances mécaniques de plusieurs EPs disponibles sur le marché ont ensuite été évaluées sur différents essais de plus en plus proches des conditions in vivo subies par ces dispositifs. Les EPs ont ainsi été soumises à des essais de flexion pure puis à des essais combinant flexion et pressurisation. La flexibilité des EPs et la réponse mécanique de leurs composants ont été comparées. Il a été montré que l'architecture de l'EP avait une influence significative sur ses performances mécaniques. Enfin, le déploiement des EPs au sein de deux modèles d'anévrismes a été simulé, permettant de mettre en évidence d'autres complications, comme les endofuites de type I. Ces travaux ouvrent ainsi la voie à de nombreuses perspectives, et notamment au développement d'un logiciel d'aide à la décision à destination des chirurgiens

Finite element analysis of the mechanical performances of aortic stent-grafts : application to the treatment of tortuous aneurysms

Le traitement endovasculaire (EVAR) de l’anévrisme de l’aorte abdominale (AAA) vise à mettre en place une endoprothèse (EP) au sein du sac anévrismal afin d’éviter sa rupture. Si cette chirurgie a l’avantage d’être mini-invasive et de pouvoir être utilisée pour des patients non éligibles à la chirurgie ouverte classique, il existe cependant plusieurs événements indésirables, pouvant apparaître au cours du suivi du patient. Mieux connaître le comportement mécanique des EPs permettrait ainsi d’améliorer leur conception et leur durabilité, principaux verrous au recours systématique à l’EVAR. Ainsi, une méthode de modélisation numérique multi matériaux des EPs a été développée. Les modèles numériques d’EPs ont été validés à partir d’une analyse d’images 3D obtenues par tomographie aux rayons X, montrant ainsi leur fiabilité. Les performances mécaniques de plusieurs EPs disponibles sur le marché ont ensuite été évaluées sur différents essais de plus en plus proches des conditions in vivo subies par ces dispositifs. Les EPs ont ainsi été soumises à des essais de flexion pure puis à des essais combinant flexion et pressurisation. La flexibilité des EPs et la réponse mécanique de leurs composants ont été comparées. Il a été montré que l’architecture de l’EP avait une influence significative sur ses performances mécaniques. Enfin, le déploiement des EPs au sein de deux modèles d’anévrismes a été simulé, permettant de mettre en évidence d’autres complications, comme les endofuites de type I. Ces travaux ouvrent ainsi la voie à de nombreuses perspectives, et notamment au développement d’un logiciel d’aide à la décision à destination des chirurgiens.The aim of the endovascular repair (EVAR) of abdominal aortic aneurysm (AAA) is to set up a stent-graft (SG) within the aneurysm in order to avoid its rupture. This surgery is mini-invasive and can be used for patients who are ineligible for open surgery. However, complications mainly due to mechanical issues can occur during patient follow-up, such as endoleak or stenosis for example. A better knowledge of SG mechanical behaviour could be useful to improve SG design and durability which still prevents surgeons to use this treatment systematically. A new methodology to model multi-material SGs has been developed. Special attention has been paid to the mechanical characterization of stent and graft materials. SG numerical models have been qualitatively and quantitatively validated on a bending test by the means of tomographic acquisitions and image processing, showing their reliability. Mechanical performances of several marketed SGs have been assessed through various tests increasingly closer to the in vivo conditions undergone by the devices. SGs have been subjected to pure bending tests, then to tests combining bending and pressurisation. SG flexibility and components mechanical response have been compared and SGs have been ranked according to their performances. It has been shown that SG architecture has a significant influence on SG mechanical performances. Finally, SG deployment within two aneurysm models has been successfully simulated. The latter study highlighted other complications, like type I endoleak. This work has many promising perspectives, especially the development of a computer-aided surgery.Finite element analysis of the mechanical performances of aortic stent-grafts: application to the treatment of tortuous aneurysms

From acid etching treatments to tribocorrosive properties of dental implants: do some experimental results on surface treatments have an influence on the tribocorrosion behaviour of dental implants?

International audienceSurface treatments of dental implants aim at promoting osseointegration, i.e. the anchorage of the metallic part. Titanium-, grade II-V, based material is used as a bulk material for dental implants. For promoting the anchorage of this metallic biomaterial in human jaw, some strategies have been applied for improving the surface state, i.e. roughness, topography and coatings. A case study, experimental study, is described with the method of acid etching on titanium grade 4, CpTi. The main goal is to find the right proportion in a mixture of two acids in order to obtain the best surface state. Finally, a pure theoretical prediction is quite impossible and some experimental investigations are necessary to improve the surface state. The described acid etching is compared with some other acid etching treatments and some coatings available on dental implants. Thus, the discussion is focused on the tribocorrosion behaviour of titanium-based materials. The purpose of the coating is that the lifetime under tribocorrosion is limited. Moreover, the surgery related to the implantation has a huge impact on the stability of dental implants. Thus, the performance of dental implants depends on factors related to surgery (implantation) that are difficult to predict from the biomaterial characteristics. From the tribocorrosion point of view, i.e. during the mastication step, the titanium material is submitted to some deleterious factors that cause the performance of dental implants to decrease

Deployment of stent-grafts in curved aneurysmal arteries: towards a predictive numerical tool

International audienceThe mechanical behavior of aortic stent-grafts plays an important role in the success of endovascular surgery for aneurysms. In this study, finite element analysis was carried out to simulate the expansion of five marketed stent-graft iliac limbs and to evaluate quantitatively their mechanical performances.The deployment was modeled in a simplified manner according to the following steps: stent-graft crimping and insertion in the delivery sheath, removal of the sheath and stent-graft deployment in the aneurysm, application of arterial pressure.In the most curved aneurysm and for some devices, a decrease of stent-graft cross-sectional area up to 57% was found at the location of some kinks. Apposition defects onto the arterial wall were also clearly evidenced and quantified. Aneurysm inner curve presented significantly more apposition defects than outer curve.The feasibility of finite element analysis to simulate deployment of marketed stent-grafts in curved aneurysm models was demonstrated. The influence of aneurysm tortuosity on stent-graft mechanical behavior shows that increasing vessel curvature leads to stent-graft kinks and inadequate apposition against the arterial wall. Such simulation approach opens a very promising way towards surgical planning tools able to predict intra and/or post-operative short-term stent-graft complications

Computational comparison of stent-grafts: Mechanical performances within a tortuous abdominal aortic aneurysm

International audiencePas de résum

Computational comparison of stent-grafts: Mechanical performances within a tortuous abdominal aortic aneurysm

International audiencePas de résum

Mechanical performances of stent-grafts within tortuous abdominal aortic aneurysms

International audiencePas de résum

Deployment of stent grafts in curved aneurysmal arteries: toward a predictive numerical tool

International audienc