Study of the effect of friction between the ossicles of the middle ear

The human ear is a complex biomechanical system and is divided by three parts: outer, middle and inner ear. The middle ear is formed by three ossicles (malleus, incus and stapes), ligaments, muscles and tendons, that amplify the sound, sending the sound waves to the inner ear. In this work, a finite element modelling of the middle ear and ligaments was made. The connection between ossicles was achieved using contact formulation. The modelling of ligaments was based in a hyperelastic model. Studies based in the displacement field of the eardrum and footplate were made, as well as the rotation of the footplate. The stress field in the ligaments to the exterior of the ossicular chain was still analyzed. These studies were done for different friction rates, between the ossicles, and for different acoustic pressure values applied in the eardrum. We can conclude that the connection between the ossicles may be assigned by contact formulation including friction. For simulation proposes, we can assume a quasi-rigid connection between ossicles.Peer Reviewe

A biomechanical perspective on perineal injuries during childbirth

Background and objective: Childbirth trauma is a major health concern that affects millions of women worldwide. Severe degrees of perineal trauma, designated as obstetric anal sphincter injuries (OASIS), and levator ani muscle (LAM) injuries are associated with long-term morbidity. While significant research has been conducted on LAM avulsions, less attention has been given to perineal trauma and OASIS, which affect up to 90% and 11% of vaginal deliveries, respectively. Despite being widely discussed, childbirth trauma remains unpredictable. This work aims to enhance the modeling of the maternal musculature during childbirth, with a particular focus on understanding the mechanisms underlying the often overlooked perineal injuries. Methods: A geometrical model of the pelvic floor muscles (PFM) and perineum (including the perineal body, ischiocavernosus, bulbospongiosus, superficial and deep transverse perineal muscles) was created. The muscles were characterized by a transversely isotropic visco-hyperelastic constitutive model. Two simulations of vaginal delivery were conducted with the fetus in the vertex presentation and occipito-anterior position, with and without the perineum. Results: The simulation that considered the perineum exhibited higher stresses over an extended area of the PFM, which suggests that including additional structures can impact the obtained results. The maximum stretch of the urogenital hiatus was 2.94 and the maximum stress was 23.86 kPa. The perineal body reached a maximum stretch of 1.95, which was more pronounced near the urogenital hiatus, where perineal tears may occur. The external anal sphincter's transverse diameter decreased by 51% and the maximum principal stresses were observed in the area close to the perineal body, where OASIS can occur. Conclusions: The present study emphasizes the importance of including most structures involved in vaginal delivery in its biomechanical analysis and represents another step further in the understanding of perineal injuries and OASIS. The superior region of the perineal body and its connection to the urogenital hiatus and anal sphincter have been identified as the most critical regions, highly susceptible to injury

Development of shear locking-free shell elements using an enhanced assumed strain formulation

The degenerated approach for shell elements of Ahmad and co-workers is revisited in this paper. To avoid transverse shear locking effects in four-node bilinear elements, an alternative formulation based on the enhanced assumed strain (EAS) method of Simo and Rifai is proposed directed towards the transverse shear terms of the strain field. In the first part of the work the analysis of the null transverse shear strain subspace for the degenerated element and also for the selective reduced integration (SRI) and assumed natural strain (ANS) formulations is carried out. Locking effects are then justified by the inability of the null transverse shear strain subspace, implicitly defined by a given finite element, to properly reproduce the required displacement patterns. Illustrating the proposed approach, a remarkably simple single-element test is described where ANS formulation fails to converge to the correct results, being characterized by the same performance as the degenerated shell element. The adequate enhancement of the null transverse shear strain subspace is provided by the EAS method, enforcing Kirchhoff hypothesis for low thickness values and leading to a framework for the development of shear-locking-free shell elements. Numerical linear elastic tests show improved results obtained with the proposed formulation. Copyright (C) 2001 John Wiley Sons, Ltd

Quadrilateral elements for the solution of elasto-plastic finite strain problems

In this paper two plane strain quadrilateral elements with two and four variables, are proposed. These elements are applied to the analysis of finite strain elasto-plastic problems. The elements are based on the enhanced strain and B-bar methodologies and possess a stabilizing term. The pressure and dilatation fields are assumed to be constant in each element's domain and the deformation gradient is enriched with additional variables, as in the enhanced strain methodology. The formulation is deduced from a four-field functional, based on the imposition of two constraints: annulment of the enhanced part of the deformation gradient and the relation between the assumed dilatation and the deformation gradient determinant. The discretized form of equilibrium is presented, and the analytical linearization is deduced, to ensure the asymptotically quadratic rate of convergence in the Newton-Raphson method. The proposed formulation for the enhanced terms is carried out in the isoparametric domain and does not need the usually adopted procedure of evaluating the Jacobian matrix in the centre of the element. The elements are very effective for the particular class of problems analysed and do not present any locking or instability tendencies, as illustrated by various representative examples. Copyright (C) 2001 John Wiley & Sons, Ltd

Finite element modelling of sound transmission from outer to inner ear

The ear is one of the most complex organs in the human body. Sound is a sequence of pressure waves, which propagates through a compressible media such as air. The pinna concentrates the sound waves into the external auditory meatus. In this canal, the sound is conducted to the tympanic membrane. The tympanic membrane transforms the pressure variations into mechanical displacements, which are then transmitted to the ossicles. The vibration of the stapes footplate creates pressure waves in the fluid inside the cochlea; these pressure waves stimulate the hair cells, generating electrical signals which are sent to the brain through the cochlear nerve, where they are decoded. In this work, a three-dimensional finite element model of the human ear is developed. The model incorporates the tympanic membrane, ossicular bones, part of temporal bone (external auditory meatus and tympanic cavity), middle ear ligaments and tendons, cochlear fluid, skin, ear cartilage, jaw and the air in external auditory meatus and tympanic cavity. Using the finite element method, the magnitude and the phase angle of the umbo and stapes footplate displacement are calculated. Two slightly different models are used: one model takes into consideration the presence of air in the external auditory meatus while the other does not. The middle ear sound transfer function is determined for a stimulus of 60 dB SPL, applied to the outer surface of the air in the external auditory meatus. The obtained results are compared with previously published data in the literature. This study highlights the importance of external auditory meatus in the sound transmission. The pressure gain is calculated for the external auditory meatus.info:eu-repo/semantics/publishedVersio

Geometric analysis of female pelvic floor muscles by using manual segmentation

Magnetic Resonance Imaging (MRI) has been used in the diagnostic evaluation of the pelvic floor dysfunctions. MRI can contribute to generate 3D solids of pelvic floor muscles through manual segmentation. The aim of this study is to calculate the area and its moment of inertia of 8 female pelvic floor muscles by using manual segmentation technique. Based on CAD software manual segmentation was used. To build 3D reconstruction models, through of twenty consecutive images. The models were made through splines in each sketch, documenting changes in the pubovisceral muscle (a part from the pelvic floor muscles) from the pubis to coccyx. Two sketches were chosen and biomechanics properties like area and stiffness (moment of inertia) were acquired for each sketch used to generate the pubovisceral muscles. The moment of inertia of the pubovisceral muscle decreases following the order: anterior sketch and posterior sketch. Higher values for the moment of inertia can be encountered in anterior sketcher. This conclusion can lead to more stability in the anterior compartment of pelvic floor visceral

Centrality evolution of the charged-particle pseudorapidity density over a broad pseudorapidity range in Pb-Pb collisions at root s(NN)=2.76TeV

Peer reviewe

Topics in Medical Image Processing and Computational Vision

VIII, 309 p. 147 illus., 88 illus. in color.onlin

Modelling human liver microphysiology on a chip through a finite element based design approach

Organ‐on‐a‐chip (OoaC) are microfluidic devices capable of growing living tissue and replicate the intricate microenvironments of human organs in vitro, being heralded as having the potential to revolutionize biological research and healthcare by providing unprecedented control over fluid flow, relevant tissue to volume ratio, compatibility with high‐resolution content screening and a reduced footprint. Finite element modelling is proven to be an efficient approach to simulate the microenvironments of OoaC devices, and may be used to study the existing correlations between geometry and hydrodynamics, towards developing devices of greater accuracy. The present work aims to refine a steady‐state gradient generator for the development of a more relevant human liver model. For this purpose, the finite element method was used to simulate the device and predict which design settings, expressed by individual parameters, would better replicate in vitro the oxygen gradients found in vivo within the human liver acinus. To verify the model's predictive capabilities, two distinct examples were replicated from literature. Finite element analysis enabled obtaining an ideal solution, designated as liver gradient‐on‐a‐chip, characterised by a novel way to control gradient generation, from which it was possible to determine concentration values ranging between 3% and 12%, thus providing a precise correlation with in vivo oxygen zonation, comprised between 3%–5% and 10%–12% within respectively the perivenous and periportal zones of the human liver acinus. Shear stress was also determined to average the value of 0.037 Pa, and therefore meet the interval determined from literature to enhance liver tissue culture, comprised between 0.01 − 0.05 Pa