Fibre Reinforcement in Living Cells: A Preliminary Study of the F-actin Filaments

AbstractCells are continuously exposed to physical stresses and strains from the Extracellular Matrix (ECM), thus, refining through numer- ical simulations the in vitro conditions during the cultures, may likely promote adequate tissue growth and remodelling [1].This paper describes a simplified three-dimensional constitutive model of the mechanical behaviour of the living cells. The necessary continuum mechanics background is skipped, along with derivations of the stress and spatial elasticity tensors for a transversely isotropic and hyperelastic material. The particular form of the strain energy proposed by Weiss [2] is used to describe the family of fibers. Also, the implementation of hyperelastic materials resorting the commercial finite-element-software Abaqus is discussed.Numerical examples are presented that demonstrate the utility and effectiveness of this approach. More specifically, homoge- neous deformations are imposed and the results compared with the analytical solution. Also, the convergence rate is checked for each case. Following, the use of UMAT routines using jacobian material matrices based on the Jaumann rate of Kirchhoff stress tensor ensured quadratic convergence rates

Influence of the insertion speed during a straight electrode array implantation, a numerical study

Approximately 466 million people worldwide suffer from some type of hearing loss. About ninety-three percent of them are adults, aged over 15 years (World Health Organization 2018). Profound hearing loss in children lead to a deficient development of spoken language, resulting in a negative impact on daily communication. On the other hand, in adults which have acquired the profound hearing loss after having developed spoken language and cognitive abilities are able to use these skills with the help of a cochlear implant, as mentioned by Jorgensen et al. (Jorgensen et al. 2018). Cochlear implant is an electronic device implanted into the cochlea to directly stimulate the auditory nerve. This device is particularly implanted in patients with severe-to-profound hearing loss (Khater and Mohammad 2017). The surgery is safe, but involves some risks, such as infections, device malfunction which can lead to poor hearing outcome (Loundon et al. 2010). Future improvements in cochlear implant surgery will necessarily involve the decrease of the intra-cochlear damage, thus preserving the patient’s residual hearing. The mechanical properties of the electrode array components, the geometrical shape, the processor and the surgical techniques are some of the aspects that can be optimized in order to help the patients to recover their normal hearing capacities. In this work, the influence of the insertion speed during a cochlear implantation was studied. A straight electrode array was initially modelled. Many authors indicate as being the less traumatic type of cochlear implant. The electrode array was meshed with linear hexahedral elements, with reduction integration, whereas the cochlear wall was modelled with 4-node shell elements. Four different insertion speeds: 0.25, 0.5, 1 and 2m/s were investigated. The numerical simulations of the cochlear implantation carried out in Abaqus software showed the same pattern of the insertion force against insertion depth, thus indicating the different phases of the implantation. Results demonstrated that lower insertion speeds, led to a reduction on the contact pressure and insertion force. It is then expected that a lower insertion speed will allow to increase the residual hearing while reducing surgical complications.info:eu-repo/semantics/publishedVersio

Numerical study of tympanosclerosis including its effect on human hearing

Tympanosclerosis is an abnormal disorder of the middle ear or only the eardrum (i.e., myringosclerosis) in which there are calcium deposits. Normally, it is caused by recurrent middle ear infections. In this work, a 3D finite element model of the ear was developed, simulating different cases of tympanosclerosis. Through this model, the magnitude and the phase angle of the umbo and stapes displacement were obtained. The middle ear sound transfer function was determined for a stimulus of 80, 90 and 100 dB SPL, in a frequency range between 100 Hz and 10 kHz, applied on the outer surface of the eardrum in the external auditory canal. Depending on the tympanosclerosis affected area, the main conclusion is that worse results (leading to hearing loss) occur when all of the ossicular chain is affected.info:eu-repo/semantics/publishedVersio

Efeitos biomecânicos da evolução do colesteatoma sobre a corda do tímpano

A otite média crónica pode levar ao aparecimento de um tumor benigno do ouvido, chamado colesteatoma. Esta patologia, se não for devidamente tratada, pode ter graves consequências. Uma delas pode resultar em paralisia facial se comprimir um ramo do nervo facial que atravessa o ouvido médio. Neste trabalho foram avaliadas as tensões exercidas do tumor contra o nervo. A maior tensão foi obtida na área de contacto entre o nervo e a bigorna.info:eu-repo/semantics/publishedVersio

Finite element modelling of the surgical procedure for placement of a straight electrode array: Mechanical and clinical consequences

A cochlear implant is an electronic device implanted into the cochlea to directly stimulate the auditory nerve. Such device is used in patients with severe-to-profound hearing loss. The cochlear implant surgery is safe, but involves some risks, such as infections, device malfunction or damage of the facial nerve and it can result on a poor hearing outcome, due to the destruction of any present residual hearing. Future improvements in cochlear implant surgery will necessarily involve the decrease of the intra-cochlear damage. Several implant related variables, such as materials, geometrical design, processor and surgical techniques can be optimized in order for the patients to partially recover their hearing capacities The straight electrode is a type of cochlear implant that many authors indicate as being the less traumatic. From the finite element analysis conducted in this work, the influence of the insertion speed, the friction coefficient between the cochlear wall and the electrode array, and several configurations of the cochlear implant tip were studied. The numerical simulations of the implantation showed the same pattern of the insertion force against insertion depth, thus indicating the different phases of the insertion. Results demonstrated that lower insertion speeds, friction coefficients and tip stiffness, led to a reduction on the contact pressures and insertion force. It is expected that these improved configurations will allow to preserve the residual hearing while reducing surgical complications.info:eu-repo/semantics/publishedVersio

Cupula response to otoconia debris in the semicircular canal

The vertigo symptoms are commonly related with inner ear diseases and it affects 20%-30% of the world population, and its prevalence increases with age. In this work, a three-dimensional computational model of the semicircular canal of the vestibular system, containing the fluids which promote the body balance, was used. The smoothed-particle hydrodynamics method was the computational process used to simulate the fluid behaviour, in which the elements are represented by particles and have constant mass. The other vestibular components were discretized using the finite element method. The movement performed to endolymph/cupula interaction analysis was reproduced in the simulation through the acquisition of the displacement field based on image analysis. The results obtained with the frames of the video recorded during the process is the appropriate method to simulate the real moves, due to the analysis of the region of interest located near the inner ear. The data obtained from the video acquisition were the input in the simulation with the semicircular model. The principal stress cupular response allowed to understand the interaction of the vestibular structures during a vertigo episode, and the influence of the otoconia in the cupula displacement. This model is the first step to improve the vestibular rehabilitation and the quality of life of patients suffering from vertigo.info:eu-repo/semantics/publishedVersio

How the computational methods can contribute to better knowledge of the ear

The biomechanical behavior of the human ear can be studied using mathematical approaches, such as the finite element method. This methodology allows to perform simulations to evaluate the influence of sound transmission through all way of the ear, since the sound is selected by the outer ear to the inner ear. The finite element method is currently the preferred method for the numerical solution of partial differential equations, and it is used in several fields of the biological sciences. Due to its large applicability and efficiency, there are several works where this methodology is applied in different specialties, to analyze loads, strains or displacements, as in the case of the biomechanical study of the ear. From CT images, three-dimensional accurate computational models are created. The technique employs a set of calculations of numerical analysis for solutions of kinematic (displacements and rotations) and mechanical aspects (strength, stress, pressure, deformation). The use of these computer models enables the motion analysis of all ossicular chain points at any moment.info:eu-repo/semantics/publishedVersio

Computational simulation of the cupula behavior in vestibular pathologies of the inner ear

Vertigo is reported as one of the most common symptoms in the world, commonly related with vestibular disorders. It is considered the third most frequent complaint in medicine, transmitting a sense of inadequacy and insecurity, mainly in elders. The aim of this work is to contribute to a better understanding on how the vestibular system works, mainly during vestibular rehabilitation process. This knowledge will help in the development of new techniques that will facilitate a more efficient rehabilitation. Vestibular rehabilitation consists in a set of exercises, known as maneuvers, that can reduce and even eliminate the symptoms of dizziness and imbalance associated with a vestibular disorder.info:eu-repo/semantics/publishedVersio

On the hearing effects of a cholesteatoma growing: A biomechanical study

Chronic otitis media enables the appearance of a benign middle ear tumor, known as a cholesteatoma, that may compromise hearing. To evaluate the influence of a cholesteatoma growth on the hearing function, a computational middle ear model based on the finite element method was used and three different size of cholesteatoma were modeled. The cholesteatoma solidification and the consequent degradation of the ossicles were also simulated as two condition that commonly occurs during cholesteatoma evolution. A sound pressure level of 80 dB SPL was applied in the tympanic membrane and a steady state analysis was performed for frequencies from 100 Hz to 10 kHz. The displacements of both the tympanic membrane and the stapes footplate were measured. The results were compared with a healthy case and it was shown that the cholesteatoma development leads to a decrease in the umbo and stapes displacements. The ossicles degradation simulation showed the higher difference comparing with the cholesteatoma in an initial stage, with lower displacements in the stapes footplate mainly for high frequencies. The observed displacement differences are directly connected to hearing loss, being possible to conclude that cholesteatoma evolution in the middle ear will lead to hearing problems, mainly in an advanced stage.info:eu-repo/semantics/publishedVersio