Search

The spreading of respiratory diseases through deposited saliva droplets is strongly dependent on the water evaporation process that may determine the virus viability due to the increase in concentration of nonvolatile compounds that are harmful for the virus. The drying time of a virus-laden droplet is influenced by environmental conditions, such as relative humidity and temperature, physical properties, such as the features of the surface on which it is deposited, and the wetting regime. Under this perspective, we addressed the modeling of an evaporating sessile droplet resting on a flat smooth surface, extending a previous diffusion-based model from the same authors. The evaporation behavior of sessile droplets of aqueous sodium chloride solutions and the virus viability of a surrogate virus (MS2) have been simulated considering different wetting regimes to account for different types of surfaces, ranging from highly hydrophilic to highly hydrophobic, as well as different ambient conditions, in terms of temperature and relative humidity. The results of calculations were given in terms of time evolution of contact angle, contact radius, mixture volume, and salt concentration, unveiling the importance of different wetting regimes for evaporation behavior and drying time. Longer evaporation times have been observed as temperature decreases and relative humidity increases. With reference to a surrogate virus, we evaluated the virus viability at different selected conditions, observing the classical U-shape of relative viability as a function of relative humidity of the environment at a certain temperature.

Abstract Poromechanics plays a key role in modelling hard and soft tissue behaviours, by providing a thermodynamic framework in which chemo-mechanical mutual interactions among fluid and solid constituents can be consistently rooted, at different scale levels. In this context, how different biological species (including cells, extra-cellular components and chemical metabolites) interplay within complex environments is studied for characterizing the mechanobiology of tumor growth, governed by intratumoral residual stresses that initiate mechanotransductive processes deregulating normal tissue homeostasis and leading to tissue remodelling. Despite the coupling between tumor poroelasticity and interspecific competitive dynamics has recently highlighted how microscopic cells and environment interactions influence growth-associated stresses and tumor pathophysiology, the nonlinear interlacing among biochemical factors and mechanics somehow hindered the possibility of gaining qualitative insights into cells dynamics. Motivated by this, in the present work we recover the linear poroelasticity in order to benefit of a reduced complexity, so first deriving the well-known Lyapunov stability criterion from the thermodynamic dissipation principle and then analysing the stability of the mechanical competition among cells fighting for common space and resources during cancer growth and invasion. At the end, the linear poroelastic model enriched by interspecific dynamics is also exploited to show how growth anisotropy can alter the stress field in spherical tumor masses, by thus indirectly affecting cell mechano-sensing. GraphicAbstract

Langmuir monolayers at gas/liquid interfaces provide a rich framework to investigate the interplay between multiscale geometry and mechanics. Monolayer collapse is investigated at a topological and geometric level by building a scale space M from experimental imaging data. We present a general lipid monolayer collapse phase diagram, which shows that wrinkling, folding, crumpling, shear banding, and vesiculation are a continuous set of mechanical states that can be approached by either tuning monolayer composition or temperature. The origin of the different mechanical states can be understood by investigating the monolayer geometry at two scales: fluorescent vs atomic force microscopy imaging. We show that an interesting switch in continuity occurs in passing between the two scales, C

Growing biological media develop residual stresses to make compatible elastic and inelastic growth-induced deformations, which in turn remodel the tissue properties modifying the actual elastic moduli and transforming an initially isotropic and homogeneous material into a spatially inhomogeneous and anisotropic one. This process is crucial in solid tumor growth mechanobiology, the residual stresses directly influencing tumor aggressiveness, nutrients walkway, necrosis and angiogenesis. With this in mind, we here analyze the problem of a hyperelastic sphere undergoing finite heterogeneous growth, in cases of different boundary conditions and spherical symmetry. By following an analytical approach, we obtain the explicit expression of the tangent elasticity tensor at any point of the material body as a function of the prescribed growth, by involving a small-on-large procedure and exploiting exact solutions for layered media. The results allowed to gain several new insights into how growth-guided mechanical stresses and remodeling processes can influence the solid tumor development. In particular, we highlight that— under hypotheses consistent with mechanical and physiological conditions—auxetic (negative Poisson ratio) transformations of the elastic response of selected growing mass districts could occur and contribute to explain some not yet completely understood phenomena associated to solid tumors. The general approach proposed in the present work could be also helpfully employed to conceive composite materials where ad hoc pre-stress distributions can be designed to obtain auxetic or other selected mechanical properties.

Even with the most recent advances in rock mechanics, the stability assessment of underground tunnels continues to involve many uncertainties in the parameters which can significantly affect the calculated factors of safety. In the present work, a straight characterization which can help to evaluate the risk of a tunnel collapse with respect to the depth of excavation is proposed. Following a consolidated Limit Analysis approach and by means of the Hoek-Brown failure criterion, the galleries are divided into shallow, intermediate and deep according to the variability of the mechanical parameters of the rock mass with depth. A solution to the problem of impending collapse in the case of variable rock properties is proposed and examples are presented and discussed both from an analytical and a numerical standpoint.

The paper proposes a mixed strain- and stress-based topology optimization method for designing the ideal geometry of carbon fibers in composite laminates subjected to either applied tractions or prescribed displacements. On the basis of standard micromechanical approaches, analytical elastic solutions for a single cell, assumed to be a Representative Volume Element (RVE), are ad hoc constructed by involving anisotropy induced by fiber orientation and volume fraction, also taking into account inter-laminar stresses and strains. The analytical solutions are then implemented in a Finite Element (FE) custom-made topology optimization-based procedure rewritten to have as output the best curves the reinforcing fibers have to draw in any composite laminate layer to maximize the overall panel stiffness or to minimize the elastic energy. To verify the effectiveness of the proposed strategy, different structures undergoing either in-plane or out-plane boundary conditions have been selected and theoretically investigated, determining the optimal fibers' maps and showing the related results in comparison to standard sequences of alternate fibers disposition for the same composites. Two optimized panels were at the end actually produced using an innovative Automated Fiber Placement (AFP) machine and consolidating the materials by means of autoclave curing processes, in this way replicating the fiber paths obtained from theoretical outcomes. As a control, two corresponding composite structures were also built without employing the fiber optimization strategy. The panels have been tested in laboratory and the theoretical results have been compared with the experimental findings, showing a very good agreement with our predictions and confirming the capability of the proposed algorithm in suggesting the arrangement of the fibers to obtain enhanced mechanical performances. It is felt that the hybrid analytical-FE topology optimization strategy, in conjunction with the possibilities offered by AFP devices, could pave the way for a new generation of ultra-lightweight composites for aerospace, automotive and many industrial applications.

In this paper, a first insight into the role that non-conventional structural patterns might play in the design of tall buildings is presented. The idea is to explore the mechanical properties of selected non-conventional structural patterns, in the form of both regular (Hexagrid) and irregular (Voronoi tessellation inspired) arrays, in order to assess their actual applicability in tall building design. For this aim, the concept of Representative Volume Element (RVE) and a classical homogenization-based micromechanical approach are employed for identifying the pattern units and deriving the relevant generalized stress-strain relationships. In the case of irregular patterns based on Voronoi diagrams, obtained by perturbing prescribed key geometrical features of hexagrids, a statistically significant sample of RVEs is defined on the basis of sensitivity analyses, and the related mechanical characterization is developed in statistical terms. Finally, a preliminary stiffness-based design procedure is proposed and applied to a tall building model with Voronoi exoskeleton. In conclusion, a discussion on the effectiveness of the design procedure and on the structural efficiency of the Voronoi patterns for tall buildings is presented.

Langmuir monolayers at gas/liquid interfaces provide a rich framework to investigate the interplay between multiscale geometry and mechanics. Monolayer collapse is investigated at a topological and geometric level by building a scale space M from experimental imaging data. We present a general lipid monolayer collapse phase diagram, which shows that wrinkling, folding, crumpling, shear banding, and vesiculation are a continuous set of mechanical states that can be approached by either tuning monolayer composition or temperature. The origin of the different mechanical states can be understood by investigating the monolayer geometry at two scales: fluorescent vs atomic force microscopy imaging. We show that an interesting switch in continuity occurs in passing between the two scales, C A F M ∈ M A F M ≠ C F M ∈ M . Studying the difference between monolayers that fold vs shear band, we show that shear banding is correlated to the persistence of a multi-length scale microstructure within the monolayer at all surface pressures. A detailed analytical geometric formalism to describe this microstructure is developed using the theory of structured deformations. Lastly, we provide the first ever finite element simulation of lipid monolayer collapse utilizing a direct mapping from the experimental image space M into a simulation domain P . We show that elastic dissipation in the form of bielasticity is a necessary and sufficient condition to capture loss of in-plane stability and shear banding.

Background The aim of the study was to compare the bone mineral density changes between unmatched patients undergoing total hip arthroplasty receiving uncemented and cemented type of implants. Previous studies have used DEXA or a two dimensional analysis to estimate the bone quality following total joint replacement, whereas this study presents the changes in three dimensions. Methods Fifty subjects both male and females receiving both cemented and uncemented type of implant were recruited. Two CT scans were taken of each subject, the first at 24 h post surgery and the second one 1 year after surgery. The scans were calibrated using a phantom converting the Hounsfield units to bone mineral density values in g/cm3. The two scans were registered together using anatomical landmarks and resliced to compare the two femurs in the identical frame of reference. The bone density gain and loss was calculated by comparing density values between the two sets of scans. Findings The results showed that most of the bone loss was located around the Lesser Trochanter and some bone density gain at the distal tip of the implant. The three dimensional density changes occur differently between individuals and the study showed no correlation of bone loss with age. Interpretation The bone loss occurred mostly at the proximal femur, which is in agreement with previously presented studies. By carrying out three dimensional analysis on the bone gain and loss on the femur, it is possible to identify the patients that are showing high degree of bone loss.

The evolution of species is governed by complex phenomena in which biological and environmental features may interact dynamically. Subterranean mammals dig tunnels whose diameter minimizes energetic costs during excavations and display anatomical adaptations in order to burrow structurally stable tunnels according to specific features of the soil. These animals weight from less than 50 g up to 1–2 kg, and dig tunnels with diameters from 3 to 15 cm. The use of allometric laws has enabled these data to be correlated. However, since tunnels need to be stable with respect to the geomechanical characteristics of the resident soils, a mathematical treatment linking the admissible dimensions of tunnels to the environment here suggests a mechanically grounded correlation between the body mass of subterranean mammals and the maximum dimensions of tunnels. Remarkably, such theoretical findings reflect very well the empirical allometric relationship and contribute to explain the wide differences observed in body sizes of subterranean mammals. In this respect, a far from ancillary role of environmental mechanics on the morphological evolution of subterranean mammals can be hypothesized.

Clustering of ligand-binding receptors of different types on thickened isles of the cell membrane, namely lipid rafts, is an experimentally observed phenomenon. Although its influence on cell's response is deeply investigated, the role of the coupling between mechanical processes and multiphysics involving the active receptors and the surrounding lipid membrane during ligand-binding has not yet been understood. Specifically, the focus of this work is on G-protein-coupled receptors (GPCRs), the widest group of transmembrane proteins in animals, which regulate specific cell processes through chemical signalling pathways involving a synergistic balance between the cyclic Adenosine Monophosphate (cAMP) produced by active GPCRs in the intracellular environment and its efflux, mediated by the Multidrug Resistance Proteins (MRPs) transporters. This paper develops a multiphysics approach based on the interplay among energetics, multiscale geometrical changes and mass balance of species, i.e. active GPCRs and MRPs, including diffusion and kinetics of binding and unbinding. Because the obtained energy depends upon both the kinematics and the changes of species densities, balance of mass and of linear momentum are coupled and govern the space-time evolution of the cell membrane. The mechanobiology involving remodelling and change of lipid ordering of the cell membrane allows to predict dynamics of transporters and active receptors -in full agreement with experimentally observed cAMP levels- and how the latter trigger rafts formation and cluster on such sites. Within the current scientific debate on Severe Acute Respiratory Syndrome CoronaVirus 2 (SARS-CoV-2) and on the basis of the ascertained fact that lipid rafts often serve as an entry port for viruses, it is felt that approaches accounting for strong coupling among mechanobiological aspects could even turn helpful in better understanding membrane-mediated phenomena such as COVID-19 virus-cell interaction.

Mechanical stress accumulating during growth in solid tumors plays a crucial role in the tumor mechanobiology. Stresses arise as a consequence of the spatially inhomogeneous tissue growth due to the different activity of healthy and cancer cells inhabiting the various districts of the tissue, an additional piling up effect, induced by stress transferring across the scales, contributing to determine the total stress occurring at the macroscopic level. The spatially inhomogeneous growth rates accompany nonuniform and time-propagating stress profiles, which constitute mechanical barriers to nutrient transport and influence the intratumoral interstitial flow, in this way deciding the starved/feeded regions, with direct aftereffects on necrosis, angiogenesis, cancer aggressiveness and overall tumor mass size. Despite their ascertained role in tumor mechanobiology, stresses cannot be directly appraised neither from overall tumor size nor through standard non-invasive measurements. To date, the sole way for qualitatively revealing their presence within solid tumors is ex vivo, by engraving the excised masses and then observing opening between the cut edges. Therefore, to contribute to unveil stresses and their implications in tumors, it is first proposed a multiscale model where Volterra-Lotka (predator/prey-like) equations describing the interspecific (environment-mediated) competitions among healthy and cancer cells are coupled with equations of nonlinear poroelasticity. Then, an experimental study on mice injected subcutaneously with a suspension of two different cancer cell lines (MiaPaCa-2 and MDA.MB231) was conducted to provide experimental evidences that gave qualitative and some new quantitative confirmations of the theoretical model predictions.

Adhesive attachment systems consisting of multiple tapes or strands are commonly found in nature, for example in spider web anchorages or in mussel byssal threads, and their structure has been found to be ingeniously architected in order to optimize mechanical properties: in particular, to maximize dissipated energy before full detachment. These properties emerge from the complex interplay between mechanical and geometric parameters, including tape stiffness, adhesive energy, attached and detached lengths and peeling angles, which determine the occurrence of three main mechanisms: elastic deformation, interface delamination and tape fracture. In this paper, we introduce a formalism to evaluate the mechanical performance of multiple tape attachments in different parameter ranges, where an optimal (not maximal) adhesion energy emerges. We also introduce a numerical model to simulate the multiple peeling behaviour of complex structures, illustrating its predictions in the case of the staple-pin architecture. Finally, we present a proof-of-principle experiment to illustrate the predicted behaviour. We expect the presented formalism and the numerical model to provide important tools for the design of bioinspired adhesive systems with tuneable or optimized detachment properties.

OBJECTIVES Reinforcements for the pulmonary autograft (PA) in the Ross operation have been introduced to avoid the drawback of conduit expansion and failure. With the aid of an in silico simulation, the biomechanical boundaries applied to a healthy PA during the operation were studied to tailor the best implant technique to prevent reoperation. METHODS Follow-up echocardiograms of 66 Ross procedures were reviewed. Changes in the dimensions and geometry of reinforced and non-reinforced PAs were evaluated. Miniroot and subcoronary implantation techniques were used in this series. Mechanical stress tests were performed on 36 human pulmonary and aortic roots explanted from donor hearts. Finite element analysis was applied to obtain high-fidelity simulation under static and dynamic conditions of the biomechanical properties and applied stresses on the PA root and leaflet and the similar components of the native aorta. RESULTS The non-reinforced group showed increases in the percentages of the mean diameter that were significantly higher than those in the reinforced group at the level of the Valsalva sinuses (3.9%) and the annulus (12.1%). The mechanical simulation confirmed geometrical and dimensional changes detected by clinical imaging and demonstrated the non-linear biomechanical behaviour of the PA anastomosed to the aorta, a stiffer behaviour of the aortic root in relation to the PA and similar qualitative and quantitative behaviours of leaflets of the 2 tissues. The annulus was the most significant constraint to dilation and affected the distribution of stress and strain within the entire complex, with particular strain on the sutured regions. The PA was able to evenly absorb mechanical stresses but was less adaptable to circumferential stresses, potentially explaining its known dilatation tendency over time. CONCLUSIONS The absence of reinforcement leads to a more marked increase in the diameter of the PA. Preservation of the native geometry of the PA root is crucial; the miniroot technique with external reinforcement is the most suitable strategy in this context.

Urban densification represents one of the biggest universal challenges of contemporary cities: the increase of urban population requires new spaces to accommodate the growing demand for housing, working and tertiary activities. However, the land available for new constructions in highly urbanized areas is very limited. In this framework, the vertical extension of existing buildings is the most sustainable strategy and fascinating. Masonry structures , constituting a major part of the built stock in the historical city centres of several European countries, are particularly suitable for vertical addition of extra-floors, since they generally exhibit an adequate overstrength for bearing an increase of gravity loads, although seismic retrofit interventions are usually required. In this paper, starting from the case study of the historical town of Pozzuoli, in South Italy, an “antifragile” approach, based on the intermediate isolation system, is suggested to rise the height of the masonry building , while reducing the global seismic demand. For this aim, in this paper are analysed the architectural-functional and structural design issues related to a vast-scale application of vertical additions isolated on the top of existing structures. Further, the feasibility and effectiveness of the strategy are discussed, and benefits in terms of seismic performance are evaluated.

Ischemic mitral regurgitation (IMR) is a form of mitral insufficiency that is characterized by papillary muscle (PM) displacement, leaflet tethering, reduced closing forces, and different degree of annular dilatation. Treatment of this condition includes mitral valve replacement or mitral valve repair with restrictive annuloplasty. Recent evidences in mitral valve repair showed that addressing only the annulus and neglecting the subvalvular apparatus provides a suboptimal operation with poor long-term results. However, the complexity of the geometrical aberrances occurring in IMR demands for more accurate analysis also involving the biomechanics underlying the failing mitral valve and subvalvular apparatus. Finite element analysis (FEA) is a powerful tool in this context and we developed a biomechanical model of mitral valve and subvalvular unit using 3D geometry of the leaflets, annulus, chordae and PM. After the application of structural properties of materials to these elements and simulation of systemic pressure loading, FEA could be used to directly determine biomechanical changes and geometry variations. We believe this approach can provide valuable information to better address the surgical treatment of IMR and answer some of the questions still pending in IMR management.

The failure of mitral valve repair procedures revealed in the outcomes of the recent randomized studies is suggesting the necessity for a better understanding of the biomechanical mechanisms underlying the failure of the surgical approaches. Use of biomechanical modelling and finite element analysis (FEA) in cardiovascular research is an important aid in this context. In our group we developed a biomechanical model taking into account all the component of the mitral valve functional unit including the valve leaflets, the annulus, the papillary muscles, the chordae tendinea and the ventricular geometry. The two-dimensional mathematical model was capable to predict some of the actual geometrical and mechanical features of the valvular and subvalvular apparatuses in physiological and pathological conditions providing the engineering quantitative relations between closing and tethering forces and the mechanisms governing the mitral valve unit function. This model might further become patient-specific by means of 3D reconstruction of clinical imaging. Images are first converted in a standard vector format (DICOM, etc.), then automatically translated in a "structural" finite element model and finally implemented in a finite element code. This allows for in silico simulations to virtually explore the effects of different surgical approaches at an early stage after the procedure, to help the operative decision processes, or to optimize the design of surgical implants.

Acoustophoresis devices are proposed as tools for manipulation and diagnostic in microfluidic environments. We demonstrate that their diffusion can be supported and enhanced by Digital Holography. Indeed, this technique covers all the current imaging needs and can stimulate the development of novel applications thanks to its unique features. The numerical refocusing is exploited to control the manipulation during acoustic focusing and acoustic-driven aggregation and to retrieve the 3D trajectories of tracer beads for the ultrasound field calibration. Besides tracking, DH displays its full potential when USs are used to directly manipulate or deform cells. In this case, numerical processing provides information on the sample movement and morphology, with potential applications in the field of diagnostic.

The combination of Digital holography and acoustofluidics provides distinct advantages. While a transparent piezo assures optical investigation through the microchannel, we employ holographic imaging to assess the acoustic manipulation and to calibrate bulk acoustic waves.

Strategies to reduce leakage based on integrated systems of monitoring and management of the pressure levels and related anomalies are acknowledged as the most reliable and cost-effective techniques to improve the efficiency of water networks. Because of their relevant impact at the large scale and the crucial roles currently played by programs envisaging ideas of smart cities capable to control/solve problems of homeland security and prevention and early monitoring of disasters and natural hazards, assessment and optimization of water networks have gained interest in recent years, overcoming the scientific fences of civil and hydraulic engineering and now being at the center of a wider vivid debate on how to maximize theoretical and experimental methods to increase security, reliability, and the so-called resilience of urban centers. Within this general scenario, this paper approaches the problem of the monitoring of leakage phenomena by focusing on the possibility of tracing the effects of the presence of not-necessarily circular holes on pipes subjected to combined water pressure and bending regimes, conceiving a parametric model which includes size, shape, orientation, and positioning of the hole, as well as different boundary conditions in the analyses to establish how they influence the final leakage. Sensitivity finite-element–based analyses are conducted to derive curves which could in principle serve, in combination with other consolidated strategies, to better identify position and amount of leakage phenomena. The outcomes are compared with the literature and in-house full-scale experimental findings, demonstrating good agreement between theoretical outcomes and laboratory results and gaining insight into advantages and limitations of the proposed strategy. It is felt that the developed approach, integrated with consolidated monitoring systems, might be useful to scientists and civil engineers in the management of existing hydraulic networks to estimate leakage volumes and predict more-realistic scenarios and related solutions for designing and planning practical interventions. This paper principally focuses on the hole geometry and position aspects, without addressing the hydraulic topic of discharge coefficient, in order to better understand the behavior of a leaking pipe.

This article outlines the methods and applications of threshold-based techniques to assess in vivo muscle and bone tissue distribution in normal and pathological conditions using computed tomography imaging. The approaches described here use medical imaging processing techniques and computational methods to study bone mechanical proprieties, analyze and quantify muscle morphology, visualize changes with 3-D models, develop subject-specific numerical profiles, and assess muscle and bone changes during clinical treatments.

The pulmonary artery autograft (PA) is the ideal substitute for aortic valve disease in children and young adult. However, it is harnessed by the issue of long-term dilation and regurgitation, often requiring surgery. PA implanted in aortic position during the growth phase in children undergoes a process of mechanical remodeling. We previously developed a semiresorbable armored prosthesis able to mechanically sustain the neoaorta preventing dilation and to gradually integrate with the PA wall inducing a progressive arterial-like tissue positive remodeling. We also described the mechanisms of growth, remodeling and stress shielding of the reinforced PA through a mathematical model. We sought to demonstrate the biological counterpart and the potential molecular mechanisms underlying this histological and mechanical remodeling. A specific mathematical model was developed to describe mechanical behavior of the PA. Mallory trichrome red staining and immunohistochemistry for MMP-9 were performed to elucidate extracellular matrix remodeling phenomena. Apoptosis and cell proliferation were determined by TUNEL assay and immunohistochemistry for Ki67, respectively. An histological remodeling phenomenon sustained by increased level of MMP-9, augmented cell proliferation and reduced apoptosis in the reinforced PA was demonstrated. The mathematical model predicted the biomechanical behavior subtended by the histological changes of the PA in these settings. Changes in metalloproteinases (MMP-9), cell proliferation and apoptosis are the main actors in the remodeling process occurring after transposition of the PA into systemic regimens. Use of semiresorbable reinforcements might induce a positive remodeling of the PA in the context of Ross operation. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 104A: 2785-2793, 2016.

Wrinkling has recently attracted an increasing interest by suggesting a number of unforeseeable applications in many emerging material science and engineering fields. If guided and somehow designed, wrinkles could be in fact used as an alternative printing way for realizing complex surface geometries and thus employed as an innovative bottom-up process in the fabrication of nano- and micro-devices. For these reasons, the prediction of wrinkles of films adhering on flat as well as on structured substrata is a challenging task, genesis and development of the phenomenon being not yet completely understood both when thin membranes are coupled with soft supports and in cases where the geometry of the surfaces are characterized by complex three-dimensional profiles. Here we investigate the experimental formation of new intriguing and somehow unforeseeable wrinkled patterns achieved on periodic structures, by showing prediction through a new hybrid analytical-numerical strategy capable to overcome some common obstacles encountered in modeling film wrinkling on flat and 3D-shaped substrata. The proposed approach, which drastically reduces the computational effort, furnishes a helpful way for predicting both qualitative and quantitative results in terms of wrinkling patterns, magnitude and wavelength, by also allowing to follow the onset of film instabilities and the progressive evolution of the phenomenon until its final stage. Keywords: Thin film, Wrinkling, PDMS substrates, Lithium niobate crystals, FEM simulations

Total Hip Arthroplasty requires pre-surgical evaluation between un-cemented and cemented prostheses. A Patient with intra-operative periprosthetic fracture and another with a successful outcome were recruited, and their finite element models were constructed by processing CT data, assuming elastic-plastic behavior of the bone as function of the local density. To resemble the insertion of the prosthesis into the femur, a fictitious thermal dilatation is applied to the broach volume. Strain-based fracture risk factor is estimated, depicting results in terms of the total mechanical strain expressed using a simple "traffic lights" color code to provide immediate, concise, and intelligible pre-operative information to surgeons.

Computed tomography (CT) provides both anatomical and density information about tissues. Bone is segmented by raw images and Finite Element Method (FEM) voxel-based meshing technique is achieved by matching each CT voxel to a single finite element (FE). As a consequence of the automated model reconstruction, unstable elements - i.e. elements insufficiently anchored to the whole model and thus potentially involved in partial rigid body motion - can be generated, a crucial problem in obtaining consistent FE models, hindering mechanical analyses. Through the classification of instabilities on topological connections between elements, a numerical procedure is proposed in order to avoid unconstrained models.

The integration of digital holography (DH) imaging and the acoustic manipulation of micro-particles in a microfluidic environment is investigated. The ability of DH to provide efficient 3D tracking of particles inside a microfluidic channel is exploited to measure the position of multiple objects moving under the effect of stationary ultrasound pressure fields. The axial displacement provides a direct verification of the numerically computed positions of the standing wave's node, while the particle's transversal movement highlights the presence of nodes in the planar direction. Moreover, DH is used to follow the aggregation dynamics of trapped spheres in such nodes by using aggregation rate metrics.

We demonstrate a 3D holographic tracking method to investigate particles motion in a microfluidic channel while unperturbed while inducing their migration through microfluidic manipulation. Digital holography (DH) in microscopy is a full-field, label-free imaging technique able to provide quantitative phase-contrast. The employed 3D tracking method is articulated in steps. First, the displacements along the optical axis are assessed by numerical refocusing criteria. In particular, an automatic refocusing method to recover the particles axial position is implemented employing a contrast-based refocusing criterion. Then, the transverse position of the in-focus object is evaluated through quantitative phase map segmentation methods and centroid-based 2D tracking strategy. The introduction of DH is thus suggested as a powerful approach for control of particles and biological samples manipulation, as well as a possible aid to precise design and implementation of advanced lab-on-chip microfluidic devices.

In recent years, experimental evidences have suggested important direct implications of viscoelasticity of human cells and cell cytoskeleton dynamics on some relevant collective and single-cell behaviors such as migration, adhesion, and morphogenesis. Consequently, the mechanical properties of single cells and how cells respond to mechanical stimuli have been at the center of a vivid debate in the scientific community. By referencing important experimental findings from the literature that have shown that human metastatic tumor cells are approximately 70% softer than benign cells, independently from the cell lines examined, the present authors have very recently theoretically demonstrated that these differences in stiffness might be exploited to mechanically discriminate healthy and cancer cells, for example, through low-intensity therapeutic ultrasound. In particular, by using a generalized viscoelastic paradigm combining classical and fractional derivative-based models, it has been found that selected frequencies (from tens to hundreds of kilohertz) are associated with resonancelike phenomena that are prevailing on thermal fluctuations and hence could be, at least in principle, helpfully utilized for both targeting and selectively attacking tumor cells. With the aim of investigating the effect of the prestress (for instance, induced in protein filaments during cell adhesion) on the overall cell stiffness and, in turn, on its in-frequency response, a simple multiscale scheme is proposed in this paper to bottom-up enrich the spring-pot-based viscoelastic single-cell models by incorporating finite elasticity and thereby determining through sensitivity analyses the role played by the stretched state of the cytoskeletal elements on the cell vibration.

We use finite elasticity to examine the behavior of a lightweight mechanism for rapid, reversible, and low-power control of mechanical impedance. The device is composed of a central shaft suspended by an annular membrane of prestretched dielectric elastomer (DE), which is coated on both sides with a conductive film. Applying an electrical field across the thickness of the membrane, attractive Coulombic forces (so-called “Maxwell stresses”) are induced that (i) squeeze the annulus, (ii) relieve the membrane stress, and (iii) reduce the mechanical resistance of the elastomer to out-of-plane deflection. This variable stiffness architecture was previously proposed by researchers who performed an experimental implementation and demonstrated a 10 × change in stiffness. In this manuscript, we generalize this approach to applications in aerospace and robotics by presenting a complete theoretical analysis that establishes a relationship between mechanical impedance, applied electrical field, device geometry, and the constitutive properties of the dielectric elastomer. In particular, we find that the stiffness reduction under applied voltage is non-linear. Such decay is most significant when the Maxwell stress is comparable to the membrane prestress. For this reason, both the prestretch level and the hyperelastic properties of the DE membrane have a critical influence on the impedance response.

No abstract available.

Ischemic mitral regurgitation (IMR) occurs as an adverse consequence of left ventricle remodeling post-myocardial infarction. A change in mitral valve configuration with an imbalance between closing and tethering forces underlie this pathological condition. These abnormalities lead to impaired leaflet coaptation and a variable degree of mitral regurgitation, which can in turn influence the ventricular filling status, the heart rhythm and the afterload regardless of the residual ischemic insult. The IMR correction can be pursued through under-sizing mitral annuloplasty and papillary muscle approximation to restore the mitral valve and left ventricle physiological geometry to, consequently, achieve normalization of the engaged physical forces. Because the structures involved undergo extremely large deformations, a biomechanics model based on the Euler&rsquo, s Elastica &ndash, the mitral leaflet&ndash, interlaced with nonlinear chordae tendineae anchored on papillary muscles has been constructed to elucidate the interactions between closing and tethering forces. The model takes into account the actual updated geometrical and mechanical features of the valvular and subvalvular apparatuses in physiological and IMR conditions, as well as in case of papillary muscle approximation, finally furnishing ad hoc geometry-based mathematical relations that could be utilised to support&mdash, and optimize&mdash, the relevant choices in cardiac surgery.

Object of the paper is to show the exact analytical solutions for the elastic response of a solid circular cylinder composed by the assembly of a central core and n surrounding hollow phases, all made of different homogeneous elastic materials, under de Saint Venant load conditions, finally obtaining for the whole object an equivalent one-dimensional homogenized beam model. In particular, the exact solution for the case of combined shear and bending is new for this type of heterogeneous compound materials, and hence it can turn useful for the comparison with other classical simplified solutions widely adopted in practical engineering problems. The analytical procedure, producing overall elastic relationships between generalized stresses and strains for Functionally Graded Material Cylinders (FGMCs) in cases of axial force, torque, bending and shear, leads to register possible large increases of selected homogenized stiffness coefficients as effect of mutual interactions among the constituents mediated by their different Poisson ratios. The special case of negative Poisson ratios is then considered, envisaging the possibility of exploiting their relevant effects on the overall stiffness of the heterogeneous media in the design of new materials, starting from the particular microstructures or work processes. At the end, some example applications and sensitivity analyses are shown for two-phase cylinders.

In this two-part set of articles the capacity load of circular rings under external pressure is investigated assuming as a starting point the classic Levy–Timoshenko approach, which is still at the bases of most design codes for cylindrical shells. This first paper presents a perfected analytical formulation of the problem, which accurately accounts for the onset of plasticity and incorporates the effect of various geometrical imperfections. A rigorous non-linear formulation is first derived and, subsequently, an algebraic expression which avoids the recourse to numerical solution strategies is established.

In this second of the two-part series of articles on the assessment of the loading capacity of circular rings and cylindrical shells under external pressure, a comparative study of the analytical formulation of Part 1 with design codes prescriptions, FEM analyses and experimental results is presented.

In the present work, the overall nonlinear elastic behaviour of a one-dimensional multi-modular structure incorporating possible imperfections at the discrete (microscale) level is derived with respect to both tensile and compressive applied loads. The model is built up through the repetition of n units, each one comprising two rigid rods having equal lengths, linked by means of pointwise constraints capable of elastically limiting motions in terms of relative translations (sliders) and rotations (hinges). The mechanical response of the structure is analysed by varying the number n of the elemental moduli, as well as in the limit case of an infinite number of infinitesimal constituents, in light of the theory of (first-order) structured deformations (SDs), which interprets the deformation of any continuum body as the projection, at the macroscopic scale, of geometrical changes occurring at the level of its sub-macroscopic elements. In this way, a wide family of nonlinear elastic behaviours is generated by tuning internal microstructural parameters, the tensile buckling and the classical Euler's elastica under compressive loads resulting as special cases in the so-called continuum limit —say when n → ∞ . Finally, by plotting the results in terms of the first Piola–Kirchhoff stress versus macroscopic stretch, it is for the first time demonstrated that such SD-based one-dimensional models can be used to generalize some standard hyperelastic behaviours by additionally taking into account instability phenomena and concealed defects.

While innovative processes take continuously place in tunneling, which remains a rapidly evolving technology, the reliable prediction of impending collapse of roofs appears still one of the most difficult tasks in civil engineering. On the basis of a theoretical approach recently proposed by the present authors, a comprehensive analytical solution for collapse mechanisms in tunnels with arbitrary excavation profiles in plastic Hoek–Brown rock masses is presented and discussed. Special attention is given to examples concerning circular tunnels and the results allow some interesting considerations on the mechanics of collapse.

A new type of sensor for distributed strain or temperature readings on structures, based on the use of Optical Fibres (OF) utilising the Brillouin scattering effect, has been recently proposed. The use of this new sensor has been successfully carried out not only in laboratory, but also in field tests on bridges and dams. As a matter of fact, several authors have shown that, by means of distributed experimental strain readings, it is easy the safety monitoring and assessment of large structures as bridges, pipes, high rise buildings, dams and tunnels. Moreover, the greatest utility of this new sensors is demonstrated by the present Authors to detect the raising of defects in large structures, and accuracy and reliability of measurements are discussed. Some uncertainties of this kind of measure related both to mechanical aspects of the sensor response and to the optical signal processing are still present. In particular, the mechanical response of optical fibre, when bonded on a straining structure was deeply addressed by some of the present Authors. The sensors were modelled in the framework of elastic Functionally Graded Material Cylinders (FGMCs), under symmetrical load conditions. Analytical closed form solutions both for the decaying and for non-decaying cases were already found and also assessed from the experimental point of view. In particular, for the application of these sensors to the interesting case of rods and wires, which constitute elements widely present in many types of bridge structures, the theoretical mechanical response of the sensors connected to the elements to be monitored, was already obtained. The base theoretical results already carried out, have shown that thanks to the embedding technique of the bonding of the sensor to the rod element, a non-decaying response of the optical sensor should be expected. Indeed, in this case, the axial strain transmitted by the deforming rod to the central glass core of the optical fibre, should equate with the supporting one. With the aim to show consistency and accuracy of the proposed theory concerning the mechanical response of the couple rod-OF-sensor (OFS), in the present work laboratory tests are carried out on aluminium large rods in extension, equipped with embedded-type optic fibre sensors. Experimental strains read by means of embedded OFS, showed very good agreement with the forecasts obtained by means of the above cited theory. This result confirms, from the experimental point of view, the reliability of the theoretical provisions. In particular, the adopted measuring technique, which utilises embedded OFS, shows great consistency and accuracy for a class of important problems related to rod structures. Rods are commonly used in several structural systems, such as trusses, suspension or cable-stayed bridges. Currently, some experiments are under preparation for the detection of surface deficiencies on high strength steel bridge wire surface, using the new Optical Fibre Sensors. The work on the bridge wire application is a joint research effort between the University of Naples Federico II and Bridge Technology Consulting in the United States. Finally, the characterization of the mechanical response of optical fibres, joined with some new solutions obtained for FGMCs, leads to a very accurate calibration of the sensors when they are utilised for strain distributed readings.

Recently, the use of Optical Fiber Sensors (OFS) utilizing Brillouin scattering effect for reading distributed measurements of temperature and strains has been addressed. Several authors have stressed the actual theoretical and practical difficulties connected to this new kind of measurement such as mechanical characterization of optical fibers, decaying of strains in the protective coatings, spatial resolution of the Brillouin scattering, brittleness of the glass core, elastic-plastic response of the coatings, end effects, and different effects of strain readings in dilatation or in contraction. Moreover for strain readings, a few technical devices have been proposed to connect the optical fiber sensor to the structure, in order to obtain better results in terms of accuracy of measurements. Recently, several authors have shown that, by means of distributed experimental strain readings, the safety monitoring and assessment of large structures as bridges, pipes, high rise buildings, dams, and tunnels is made easier. In spite of the above mentioned uncertainties, the greatest utility of these new sensors is demonstrated by the authors for detection of defects rising in large structures, and accuracy and reliability of measurements are discussed. A recent paper by some of these authors has provided for the mechanical response of optical fiber, when it is embedded in a bearing supported beam-like element, where OFSs are treated in the framework of elastic Functionally Graded Material Cylinders, under symmetrical load conditions. The achieved theoretical results characterize the complete set of the so-called no-decaying solutions, which present axial strain in the system core-jacket not varying with the radius, and hence equal to the value assumed in the supporting element. Those analytical solutions are particularly efficient for strain readings utilizing embedded sensors, because in this case the fiber core should exhibit an axial strain equal to the one on the structure to which the sensor is linked. Moreover, another set of so-called decaying solutions is obtained which was evaluated for the rate of decaying of the axial strain between the core and the support. In Part II of the current work laboratory tests will be shown, carried out on aluminium large rods in extension, equipped with embedded-type optic fiber sensors. Rods are commonly used in several structural systems, such as trusses, suspension, or cable-stayed bridges.

In the framework of classical plasticity, even when limit multipliers and collapse mechanisms associated with different loads independently acting on a solid or structure are known, not much can be inferred on the limit multiplier of the combined loading. Frame structures under the action of dead loads and seismic forces, soil–foundation interaction problems, tunnels under a variety of loads, deepwater pipelines subject to bending and pressure constitute only a few selected examples for which some sort of superposition rule, as well as bounding techniques, would be extremely useful. The present paper introduces a set of theorems for bounding limit multipliers for combined loads. In particular, ranging from a minimum knowledge about the critical state under a particular loading to a reasonable guess of the kinematics of the problem under combined loads, more and more refined bounds for the overall limit multiplier are derived. The results, to the best of the authors’ knowledge, are novel and a few examples showing their practical value are presented and discussed.

The reliable prediction of the state of collapse in tunnels and natural cavities is still one of the most difficult tasks in rock engineering. By making reference to the Hoek–Brown failure criterion, an exact solution is presented in the realm of plasticity theory with the help of classical tools of the calculus of variations. The resulting formulae are extremely simple and can be very useful to make comparisons with empirical methods and numerical analyses. Examples by means of some widely used software packages are also provided and discussed.

Background In patients with ischemic mitral regurgitation, leaflet prolapse requires an accurate evaluation since surgical approach depends on valvular and subvalvular characteristics. This study aims to describe a cohort of patients over a long-term follow up, analyzing survival, reoperation and predictive factors of surgical outcomes. Methods and results From March 1994 to June 2011, 75 patients with ischemic mitral regurgitation and leaflet prolapse underwent surgical myocardial revascularization and mitral valve repair (90.7%) or replacement (9.3%). Our cohort was followed up until April 2015, with a mean follow up of 7±3years. Cardiac-related deaths occurred in 26 patients, with a mean survival of 114.2months, including eight patients with in-hospital mortality. Reoperation was performed in 14 patients, due to valve repair failure. Twenty-six patients experienced moderate-to-severe mitral regurgitation. A preoperative LVEDD>62mm, LVESD>52mm, previous anteroseptal myocardial infarction, diffuse coronary artery disease, papillary anatomy type 1, partial rupture of the papillary muscle, A1-A2 scallop prolapse and postoperative mitral valve configuration (tenting area, tenting height, alfa-1 angle and alfa-2 angle) were identified as independent predictors of poor outcome. An index quantifying the stress on the annulus imparted by annuloplasty was elaborated and predicted endpoints. Conclusion Leaflet prolapse is an important entity in patients with ischemic mitral regurgitation, and its pathogenic mechanism mostly relies on papillary muscle lesion or elongation. Perioperative parameters describing geometric features of left ventricle, valvular and subvalvular components should be considered to provide a tailored approach for mitral valve repair, or to opt for immediate replacement in case of unfavorable geometry.

Background Supravalvular pulmonary stenosis (SPS) remains a worrisome complication in the long term of simple transposition of the great arteries. Issues of scar formation and inability to grow are considered at the base of this phenomenon. We pioneered the use of a tissue engineering approach to guide the maturation and the growth of pulmonary autograft in the Ross procedure with encouraging results. We therefore sought to investigate the use of a similar approach in the reconstruction of neopulmonary trunk (NPT) with the aim to recreate a vascular conduit that retains the structural architecture and the same biological potential of native pulmonary artery and prevents long-term SPS. Methods A model of NPT reconstruction in growing lambs was used. NPT was constructed with autologous pericardium and reinforced with a four-layered knitted polydioxanone mesh (PDS n=10) or left unreinforced (control n=10). Animals were left growing for 6months and angiographic and transesophageal echocardiographic measurements were performed at day 1 and at the end of the study together with histological analysis. Results Control group developed SPS while PDS reinforcement allowed a progressive increase in diameter with an optimal size to match the pulmonary artery of healthy growing controls. Histological analysis showed in the control group disruption of endothelial lining with fibrosis, while demonstrated in the PDS group a trilaminar vessel-like structure. Conclusions The bioresorbable reinforcement induced the formation over time of a neopulmonary conduit able to both face the hemodynamic load of the pulmonary system and guarantee a harmonious increase in size during the somatic growth.

The objective of this paper is to describe a different approach to modeling the material symmetry associated with singularities that can occur in curvilinear anisotropic elastic symmetries. In this analysis, the intrinsic non-linearity of a cylindrically anisotropic problem is demonstrated. We prove that a simple homogenization process applied to a representative volume element containing the cylindrical anisotropic singularity removes the singularity. This geometric and interpretive approach is an aid to better modeling of material symmetry associated with these singularities.