Finite-element simulation of residual stress induced by split-sleeve cold-expansion process of holes

A three-dimensional finite-element simulation was conducted for a split-sleeve cold-expansion process in order to determine the residual stress field around an expanded hole. The commercial FEA software DEFORM-3D\u2122, a Lagrangian implicit code designed for metal forming processes, was used to model the cold-expansion process of a fastener hole. The results show a through-thickness residual stress field in good agreement with the analytical solution developed by Guo. Moreover, the simulation has highlighted the effect of the split sleeve and the plate thickness on the residual stress field. \ua9 2007 Elsevier B.V. All rights reserved

On the Modeling of Transcatheter Therapies for the Aortic and Mitral Valves: A Review

Transcatheter aortic valve replacement (TAVR) has become a milestone for the management of aortic stenosis in a growing number of patients who are unfavorable candidates for surgery. With the new generation of transcatheter heart valves (THV), the feasibility of transcatheter mitral valve replacement (TMVR) for degenerated mitral bioprostheses and failed annuloplasty rings has been demonstrated. In this setting, computational simulations are modernizing the preoperative planning of transcatheter heart valve interventions by predicting the outcome of the bioprosthesis interaction with the human host in a patient-specific fashion. However, computational modeling needs to carry out increasingly challenging levels including the verification and validation to obtain accurate and realistic predictions. This review aims to provide an overall assessment of the recent advances in computational modeling for TAVR and TMVR as well as gaps in the knowledge limiting model credibility and reliability

Computational Analysis of Self-Expanding and Balloon-Expandable Transcatheter Heart Valves

Bicuspid aortic valve (BAV) patients are usually excluded from transcatheter aortic valve implantation (TAVI) as this valve anatomy likely leads to oval expansion. This study presents a numerical study of TAVI using both self-expanding and balloon expandable transcatheter heart valve (THV) in bicuspid patients with severe stenosis. The simulation framework included a patient-specific anatomy of the aortic root, calcifications and BAV leaflets extracted from medical imaging analysis as well as a realistic crimping and deployment of the THV. Tissue stress analysis highlighted local maxima in the contact area between the inner aortic lumen and the THV stent frame. Flow analysis based on the smoothed particle hydrodynamics (SPH) technique displayed the area at risk of paravalvular leakage (PVL). These findings provide insights on the TAVI in BAV and thus represents a further step towards the use of in-silico for the virtual planning of TAVI, aiming at improving not only the efficacy of the implantation but also the exploration of borderline anatomy as the case of TAVI in BAVs

Notes on the status and the current spread of Viburnum tinus L. (Viburnaceae) in Sicily (Italy)

The authors carried out a multi-disciplinary research in order to clarify the native status of Viburnum tinus in Sicily and update the knowledge about its current regional distribution. With this purpose, a large amount of scientific papers on forestry, botany and palaeo- and archaeobotany was consulted; more useful data issued from papers focused on local historical gardens, from archives and from herbarium specimens. The available data suggest that most of the extant nuclei may issue from the recent colonization of plants introduced just few centuries ago. Although the status of the stands found in some warm and humid sites in the surroundings of the city of Palermo and on the Sicani Mountain Range remains uncertain, with no doubt the majority of the other populations, including the seven new ones mentioned for the first time in this paper, issue from the recent spread of this species in several coastal and inland areas, a process which has been facilitated by its efficient seed dispersal strategy and its massive use as an ornamental plant in the green areas of the island

STUDIO NUMERICO DELL'EMODINAMICA IN PAZIENTI CON DISSECAZIONE AORTICA DI TIPO B

The development of type B aortic dissection (AoD) is caused by altered haemodynamic forces exerted on false and true lumina of dissected aorta. This work aims to study haemodynamic and morphological proprieties, which influence the progression or stability of type B AoD. Computational fluid-dynamic analyses were performed on three patients with type B AoD, whose two presented an aneurysm evolution and one presented no further complication connected with dissection. Blood flow features showed that the true lumen flow was laminar and uniform while false lumen flow lost the laminar characteristic with consequent vorticity formation. The entry point zone proximal to the aortic arch showed both high blood velocity and pressure connected with peaks of maximum WSS value. A negative pressure gradient between the false lumen entry and re-entry points was observed. This promotes the blood to flow towards the abdominal aorta reducing the risk of retrograde flow during systole. We concluded that fluid dynamics study of patients with type B AoD is a valid tool to identify the risk of aortic dissection progression as well as the formation of aortic dissection connected pathology

Titanium Lattice Structures Produced via Additive Manufacturing for a Bone Scaffold: A Review

The progress in additive manufacturing has remarkably increased the application of lattice materials in the biomedical field for the fabrication of scaffolds used as bone substitutes. Ti6Al4V alloy is widely adopted for bone implant application as it combines both biological and mechanical properties. Recent breakthroughs in biomaterials and tissue engineering have allowed the regeneration of massive bone defects, which require external intervention to be bridged. However, the repair of such critical bone defects remains a challenge. The present review collected the most significant findings in the literature of the last ten years on Ti6Al4V porous scaffolds to provide a comprehensive summary of the mechanical and morphological requirements for the osteointegration process. Particular attention was given on the effects of pore size, surface roughness and the elastic modulus on bone scaffold performances. The application of the Gibson-Ashby model allowed for a comparison of the mechanical performance of the lattice materials with that of human bone. This allows for an evaluation of the suitability of different lattice materials for biomedical applications

Improving damage resistance of solid-state battery cathodes with block copolymers: a non-linear diffusion-mechanics study at the microscale

Minimizing interfacial failure in the composite cathode remains a crucial challenge to unravel the full potential of all solid-state batteries (ASSBs). Polymer-based ASSBs offer promising means of minimizing those damage effects due to their high ductility. However, multicomponent polymers such as block copolymers (BCPs) are needed to meet requirements for both ionic conductivity and mechanical resistance. This study aims to provide a new insight into the combined effects of block copolymer composition (soft-to-hard phase ratio) and interfacial strength on the coupled diffusion-mechanics response of an ASSB cathode, achieved by proposing a non-linear computational micromechanics approach. The approach combines a pressure-dependent diffusion process, interfacial gap-dependent diffusivity, and advanced elasto-viscoplastic constitutive model for a BCP, and it is implemented numerically within a non-linear finite element framework. Two cathode design concepts are explored here, with and without the BCP coating. Results from these case studies suggest that there is a strong interplay between the interface strength (between active particles and the BCP matrix), the BCP material composition, and the interfacial diffusivity. It is found that interfacial damage can be minimized by increasing both the interfacial strength and the amount of the soft component in the BCP system. If the diffusivity across the interface is damage-dependent, the latter is reduced when the BCP is predominantly made of the hard phase. Ultimately, a simple sensitivity analysis reveals that interfacial strength plays a vital role in minimizing interfacial damage, while the coating thickness is the least influential design parameter

Structural Simulation of Transcatheter Heart Valve in Transcatheter Heart Valve

The durability of transcatheter heart valves (TAV) remains the main disadvantage of transcatheter heart valve implantation (TAVI) for treating aortic valve stenosis. In this study, we assessed the structural mechanics of TAV-in-TAVI using patient-specific modeling. A parametric analysis highlighted that the outcome of TAV-in-TAV depends on the implanted device position and the planned device to be implanted. Contact pressure evinced the impact of different implantation depth and device size on the TAV-in-TAV. This study may bring new insight in the biomechanical performance of TAV to evaluate options for future interventions when the current TAVs experience device failure

On the left ventricular remodeling of patients with stenotic aortic valve: A statistical shape analysis

The left ventricle (LV) constantly changes its shape and function as a response to patho-logical conditions, and this process is known as remodeling. In the presence of aortic stenosis (AS), the degenerative process is not limited to the aortic valve but also involves the remodeling of LV. Statistical shape analysis (SSA) offers a powerful tool for the visualization and quantification of the geometrical and functional patterns of any anatomic changes. In this paper, a SSA method was devel-oped to determine shape descriptors of the LV under different degrees of AS and thus to shed light on the mechanistic link between shape and function. A total of n = 86 patients underwent computed tomography (CT) for the evaluation of valvulopathy were segmented to obtain the LV surface and then were automatically aligned to a reference template by rigid registrations and transformations. Shape modes of the anatomical LV variation induced by the degree of AS were assessed by principal component analysis (PCA). The first shape mode represented nearly 50% of the total variance of LV shape in our patient population and was mainly associated to a spherical LV geometry. At Pearson’s analysis, the first shape mode was positively correlated to both the end-diastolic volume (p < 0.01, R = 0.814) and end-systolic volume (p < 0.01, and R = 0.922), suggesting LV impairment in patients with severe AS. A predictive model built with PCA-related shape modes achieved better perfor-mance in stratifying the occurrence of adverse events with respect to a baseline model using clinical demographic data as risk predictors. This study demonstrated the potential of SSA approaches to detect the association of complex 3D shape features with functional LV parameters

Primi segnali di spontaneizzazione di Schinus molle L. (Anacardiaceae) in Sicilia.

Si riportano i primi casi di naturalizzazione di Schinus molle L. (Anacardiaceae) osservati in Sicilia