Optimal design of interfaces in a femoral head surface replacement prosthesis considering nonlinear behaviour

Shape optimization problems applied in the field of biomechanics are presented. Particularly the shape optimization of interfaces separating the bone tissue from the orthopaedic implant are considered. Nonlinear interface behaviour is included in the computational models: a nonlinear elastic model and a damage based model. For the two nonlinear interface constitutive laws an analytical shape sensitivity formulation has been developed. The objective functions included both the effect of the interface stresses and of the interface micromotions. The optimization procedure provided optimal designs, which display better mechanical performance in terms of interface stresses and damage diffusion. [Author abstract; 26 Refs; In English

Optimal design of interfaces in a femoral head surface replacement prosthesis considering nonlinear behaviour

Shape optimization problems applied in the field of biomechanics are presented. Particularly the shape optimization of interfaces separating the bone tissue from the orthopaedic implant are considered. Nonlinear interface behaviour is included in the computational models: a nonlinear elastic model and a damage based model. For the two nonlinear interface constitutive laws an analytical shape sensitivity formulation has been developed. The objective functions included both the effect of the interface stresses and of the interface micromotions. The optimization procedure provided optimal designs, which display better mechanical performance in terms of interface stresses and damage diffusion. [Author abstract; 26 Refs; In English

Resistant Cases of Psoriatic Arthritis: How to Manage Them

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Short communication: Recognising the perils of landslide-generated tsunamis in the Asia–Pacific region

© 2019, Springer Nature B.V. Two recent tsunamis in Indonesia highlight the importance of submarine landslides. Although both events had different origins (volcanic, seismic), submarine landsliding was probably the key component in tsunamigenesis. While a few recent submarine landslide-generated tsunamis have been discussed in the literature, these types of events have not been seriously scrutinised by geoscientists or hazard modellers. This is most likely because of both a lack of awareness and also the common perception that such events are too remote a possibility to be of major concern. However, by catching us off-guard, these two Indonesian events have brought slope-failure tsunamigenesis into sharper focus. It is hoped that this will stimulate greater scholarship on the issue of slope-failure tsunamigenesis worldwide, with an aim to better understanding event characteristics, probabilities, and ultimately better inform existing risk reduction strategies

Machine Learning approaches for the design of biomechanically compatible bone tissue engineering scaffolds

Triply-Periodic Minimal Surfaces (TPMS) analytical formulation does not provide a direct correlation between the input parameters (analytical) and the mechanical and morphological properties of the structure. In this work, we created a dataset with more than one thousand TPMS scaffolds for the training of Machine Learning (ML) models able to find such correlation. Finite Element Modeling and image analysis have been used to characterize the scaffolds. In particular, we trained three different ML models, exploring both a linear and non-linear approach, to select the features able to predict the input parameters. Furthermore, the features used for the prediction can be selected in three different modes: i) fully automatic, through a greedy algorithm, ii) arbitrarily, by the user and iii) in a combination of the two above methods: i.e. partially automatic and partially through a user-selection. The latter, coupled with the non-linear ML model, exhibits a median error less than 3% and a determination coefficient higher than 0.89 for each of the selected features, and all of them are accessible during the design phase. This approach has been applied to the design of a hydroxyapatite TPMS scaffolds with prescribed properties obtained from a real trabecular-like hydroxyapatite scaffold. The obtained results demonstrate that the ML model can effectively design a TPMS scaffold with prescribed features on the basis of biomechanical, mechanobiology and technological constraints

Tonga volcanic eruption and tsunami, January 2022: globally the most significant opportunity to observe an explosive and tsunamigenic submarine eruption since AD 1883 Krakatau

January 2022 witnessed the violent eruption of Hunga Tonga–Hunga Haʻapai submarine volcano in the South Pacific. With a volcanic explosivity index possibly equivalent to VEI 5, this represents the largest seaborne eruption for nearly one and a half centuries since Indonesia’s cataclysmic explosion of Krakatau in AD 1883. The Tongan eruption remarkably produced ocean-wide tsunamis, never documented before in the Pacific instrumental record. Volcanically generated tsunamis have been referred to as a ‘blind spot’ in our understanding of tsunami hazards, particularly in the Pacific Ocean. This event therefore presents a unique opportunity for investigating the multiple processes contributing to volcanic tsunamigenesis. It is argued that, although challenges exist, integrating theoretical, observational, field and modelling techniques offers the best approach to improving volcanic tsunami hazard assessment across Oceania

Computational models for the simulation of the elastic and fracture properties of highly porous 3D-printed hydroxyapatite scaffolds

Bone scaffolding is a promising approach for the treatment of critical-size bone defects. Hydroxyapatite can be used to produce highly porous scaffolds as it mimics the mineralized part of bone tissue, but its intrinsic brittleness limits its usage. Among 3D printing techniques, vat photopolymerization allows for the best printing resolution for ceramic materials. In this study, we implemented a Computed micro-Tomography based Finite Element Model of a hydroxyapatite porous scaffold fabricated by vat photopolymerization. We used the model in order to predict the elastic and fracture properties of the scaffold. From the stress–strain diagram of a simulated compression test, we computed the stiffness and the strength of the scaffolds. We found that three morphometric features substantially affect the crack pattern. In particular, the crack propagation is not only dependent on the trabecular thickness but also depends on the slenderness and orientation of the trabeculae with respect to the load. The results found in this study can be used for the design of ceramic scaffolds with heterogeneous pore distribution in order to tailor and predict the compressive strength

Mechanical Properties of Robocast Glass Scaffolds Assessed through Micro-CT-Based Finite Element Models

In this study, the mechanical properties of two classes of robocast glass scaffolds are obtained through Computed micro-Tomography (micro-CT) based Finite Element Modeling (FEM) with the specific purpose to explicitly account for the geometrical defects introduced during manufacturing. Both classes demonstrate a fiber distribution along two perpendicular directions on parallel layers with a (Formula presented.) tilting between two adjacent layers. The crack pattern identified upon compression loading is consistent with that found in experimental studies available in literature. The finite element models have demonstrated that the effect of imperfections on elastic and strength properties may be substantial, depending on the specific type of defect identified in the scaffolds. In particular, micro-porosity, fiber length interruption and fiber detaching were found as key factors. The micro-pores act as stress concentrators promoting fracture initiation and propagation, while fiber detachment reduces the scaffold properties substantially along the direction perpendicular to the fiber plane