INFLUENCE of LEAFLET'S MATRIX STIFFNESS and FIBER ORIENTATION on the OPENING DYNAMICS of A PROSTHETIC TRILEAFLET HEART VALVE

Biological valves are employed for aortic valve substitution since a long time but there is a growing effort toward the development of new engineered tissues, in which the complex mechanical response of native leaflets is replicated using composite materials consisting of a soft matrix with embedded reinforcing fibers. The main goal of the present study is to investigate the influence that variations on fiber orientation and matrix stiffness may have on valve dynamics. To this aim a Fluid-Structure Interaction (FSI) model of a trileaflet valve was implemented in which the opening phase was simulated and leaflet matrix stiffness and fiber orientation were varied in the framework of an anisotropic hyperelastic strain energy function. Results show that both parameters may affect significantly transvalvular pressure gradient and effective orifice area (EOA). For the opening phase of the valve examined less favourable flow conditions were found when preferred fiber orientation is circumferential, due to lower maximum EOA achievable. Such configuration in combination with stiffer matrix may result in significant degradation of valve performances. Overall fiber orientation can potentially be taylored to optimize valve dynamics, provided also structural aspects that may be prominent in the closure phase, are considered

Integrated experimental and numerical comparison of different approaches for planar biaxial testing of a hyperelastic material

Planar biaxial testing has been applied to a variety of materials to obtain relevant information for mechanical characterization and constitutive modeling in presence of complex stress states. Despite its diffusion, there is currently no standardized testing procedure or a unique specimen design of common use. Consequently, comparison of results obtained with different configurations is not always straightforward and several types of optimized shapes have been proposed. The purpose of the present work is to develop a procedure for comprehensive comparison of results of biaxial tests carried out on the same soft hyperelastic material, using different types of gripping methods and specimen shapes (i.e., cruciform and square). Five configurations were investigated experimentally using a biaxial test rig designed and built by the authors, using digital imaging techniques to track the displacements of markers apposed in selected positions on the surfaces. Then, material parameters for a suitable hyperelastic law were determined for each configuration examined, employing an inverse method which combines numerical simulations with the finite element method (FEM) and optimization algorithms. Finally, efficiency of examined biaxial configurations was assessed comparing stress reductions factor, degree and uniformity of biaxial deformation, and operative strain ranges

Modified pseudo-elastic approach for modelling cyclic response of biological heart valves

A modified pseudo-elastic approach is proposed to model cyclic response on biological heart valves. The model takes into account hysteretic effects, in combination with hyperelastic anisotropic behaviour of valve leaflets, allowing reproduction of different loading and unloading paths. FEM implementation considered a biological heart valve during the closure phase

Simulazione FEM delle operazioni di folding e gonfiaggio di palloncini per angioplastica per il trattamento di occlusioni croniche totali in arterie periferiche

Il presente lavoro si è sviluppato nell’ambito della progettazione e ottimizzazione di un catetere endovascolare, utile al trattamento di occlusioni croniche totali (CTO) nell'arteria superficiale femorale tramite angioplastica subintimale. Per questo si è proceduto allo sviluppo di modelli agli elementi finiti per simulare la fase di gonfiaggio del palloncino, tenendo conto della complessa configurazione iniziale del pallone ripiegato all’interno del catetere sia del posizionamento in sede anatomica. In una prima fase è stato quindi modellato il processo di folding, attraverso il quale un pallone da angioplastica viene ripiegato cosicché possa essere contenuto in un diametro inscritto molto minore rispetto alla sua dimensione originale. In una seconda fase i modelli di palloni così ripiegati sono stati utilizzati come configurazione iniziale per simulazioni di gonfiaggio sia libero sia all'interno di un modello anatomico in presenza o meno di un’occlusione cronica totale (CTO)

Main drivers of the evolution of grazing in the alpine area of Valli del Leno (Trentino, Northern Italy) during the last two centuries: natural resources, labour and investments

In the Alps as in many mountain areas, livestock farming has constituted an important source of income, especially since the Middle Ages. The importance of livestock farming within the Alpine economy has changed over time due to the dynamics of supply and demand combined with evolving environmental, technological and institutional constraints. This paper focuses on the latter aspect and attempts to reconstruct how the relative importance of the production factors of land, labour and capital changed throughout the nineteenth and twentieth centuries in a mountainous area of eastern Trentino. The underlying objective of the investigation is to provide a micro-level empirical basis for hypotheses advanced in the literature regarding the evolution of a crucial sector in the Alpine economy, drawing attention to the long-term role of exogenous and endogenous factors as well as elements of continuity and change. The work is grounded in multiple sources drawn from local archives and official statistics. It demonstrates the flexibility of local communities in managing to sustainably utilize local resources over several periods.En muchas zonas de montaña la ganadería ha constituido, a partir de la Edad Media, una fuente importante de recursos económicos. La trasformación que ha habido del peso relativo de la ganadería en la economía alpina ha sido fruto de una combinación de dinámicas, por un lado concernientes a la demanda, y, por otro, de la oferta, con los cambios introducidos por los vínculos normativos medioambientales, tecnológicos e institucionales de dicha actividad. En nuestro estudio nos centramos en este último aspecto, tratando de reconstruir el cambio que ha tenido lugar en el curso de los siglos xix y xx del peso relativo de los factores de producción tierra, trabajo y capital en una zona montañosa del Trentino oriental. El objetivo principal de nuestra investigación es el de proporcionar una base empírica, en microperspectiva, a las hipótesis avanzadas en la literatura en mérito a la evolución de un sector crucial de la economía alpina, mostrando cuál ha sido a lo largo del tiempo el rol de los factores exógenos y de los endógenos y subrayando elementos de continuidad y factores de transformación

Linguistic skills in bilingual children with developmental language disorders: A pilot study

The current pilot study compared the linguistic characteristics of a cohort of simultaneous bilingual children (Italian, L1; German L2) with developmental language disorders (DLDs) and those of bilingual peers with typical language development (TLD). Importantly, the two groups were balanced for a number of environmental variables (e.g., age of first exposure to the L2, acquisition contexts, degree of exposure to both languages) known to affect linguistic development in both TLD and DLDs. The analyses included the assessment of the participants\u2019 phonological short-term memory. Their lexical, grammatical and narrative abilities were analyzed in both languages by administering the Italian and German equivalent forms of the Battery for the assessment of language in children aged 4 to 12 \u2013 BVL_4-12 (Marini et al., 2015). The children with DLDs had reduced phonological short-term memory and lexical skills that, in turn, contributed to the reduced levels of local coherence and informativeness of their narratives. Such difficulties were found at similar levels in their two languages. These results suggest that reduced phonological short-term memory and lexical selection skills may reflect a core symptom in both mono- and bilingual children with developmental language disorders

Compressive behavior of Co-Cr-Mo radially graded porous structures under as-built and heat-treated conditions

Additive manufacturing research is continuously growing, and this field requires a full improvement of the capability and reliability of the processes involved. Of particular interest is the study of complex geometries production, such as lattice structures, which may have a potentially huge field of application, especially for biomedical products.In this work, the powder bed fusion technique was utilized to manufacture lattice structures with defined building angles concerning the build platform. A biocompatible Co-Cr-Mo alloy was used. Three different types of elementary cell geometry were selected: Face Centered Cubic, Diagonal, and Diamond. These cells were applied to the radially oriented lattice structures to evaluate the influence of their orientation in relation to the sample and the build platform. Moreover, heat treatment was carried out to study its influence on microstructural properties and mechanical behavior. Microhardness was measured, and compressive tests were performed to detect load response and to analyse the fracture mechanisms of these structures.The results show that the mechanical properties are highly influenced by the cell orientation in relation to the building direction and that the properties can be further tuned via HT. The favorable combination of mechanical properties and biocompatibility suggests that Co-Cr-Mo lattices may represent an optimal solution to produce customized metal implants

Linguistic Skills in Bilingual Children With Developmental Language Disorders: A Pilot Study

The current pilot study compared the linguistic characteristics of a cohort of simultaneous bilingual children (Italian, L1; German L2) with developmental language disorders (DLDs) and those of bilingual peers with typical language development (TLD). Importantly, the two groups were balanced for a number of environmental variables (e.g., age of first exposure to the L2, acquisition contexts, degree of exposure to both languages) known to affect linguistic development in both TLD and DLDs. The analyses included the assessment of the participants’ phonological short-term memory. Their lexical, grammatical and narrative abilities were analyzed in both languages by administering the Italian and German equivalent forms of the Battery for the assessment of language in children aged 4 to 12 – BVL_4-12 (Marini et al., 2015). The children with DLDs had reduced phonological short-term memory and lexical skills that, in turn, contributed to the reduced levels of local coherence and informativeness of their narratives. Such difficulties were found at similar levels in their two languages. These results suggest that reduced phonological short-term memory and lexical selection skills may reflect a core symptom in both mono- and bilingual children with developmental language disorders

Influence of plaque properties and constitutive modeling approach on the simulation of percutaneous angioplasty of chronic total occlusions

Clinical treatment of Chronic Total Occlusion (CTO) of an artery often involves percutaneous procedures, like sub-intimal balloon angioplasty, in which the controlled inflation of a balloon restores the lumen by compression ofatherosclerotic plaque. Realistic simulations of these challenging techniques could provide valuable information for clinician, but characterization of CTO in human studies is problematic. Reported data are highly variable and the few published models employed different approaches to fit (apparently) the same experimental tests. Moreover, atherosclerotic plaques are commonly assumed as elastic and incompressible, but in angioplasty procedures they may be subjected to large and not physiological overstretch. Permanent plaque damage after balloon inflation is expected, suggesting that some form of inelastic behavior should be considered. Thus, the goal of the present work is to investigate the influence of changing plaque properties and constitutive modeling assumptions, on the predicted outcomes of a simulation of CTO percutaneous angioplasty. To this aim, a finite element model of the compression of a total occlusion inside an artery was implemented. Different forms of hyperelastic constitutive laws proposed in literature were compared in presence of the complex stress state resulting from sub-intimal angioplasty. The degree of compressibility and the threshold for a permanent damage, introduced in the form of a plastic yield limit, were varied. Overall, results demonstrated that the choice of different data sets or constitutive modeling approaches for plaque has a primary influence. Some common assumptions for plaque modeling may lead to highly variable or even unrealistic predictions for the extreme case of total occlusion treatment. In this sense, more specific experimental investigations on the properties of plaque constituents as a function of heterogeneous CTO composition, are necessary in order to exploit the potential usefulness of the method as a patient-specific predictive tool