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J R Soc Interface ; 16(154): 20190108, 2019 05 31.
Artigo em Inglês | MEDLINE | ID: mdl-31039696


Orthodontic root resorption is a common side effect of orthodontic therapy. It has been shown that high hydrostatic pressure in the periodontal ligament (PDL) generated by orthodontic forces will trigger recruitment of odontoclasts, leaving resorption craters on root surfaces. The patterns of resorption craters are the traces of odontoclast activity. This study aimed to investigate resorptive patterns by: (i) quantifying spatial root resorption under two different levels of in vivo orthodontic loadings using microCT imaging techniques and (ii) correlating the spatial distribution pattern of resorption craters with the induced mechanobiological stimulus field in PDL through nonlinear finite-element analysis (FEA) in silico. Results indicated that the heavy force led to a larger total resorption volume than the light force, mainly by presenting greater individual crater volumes ( p < 0.001) than increasing crater numbers, suggesting that increased mechano-stimulus predominantly boosted cellular resorption activity rather than recruiting more odontoclasts. Furthermore, buccal-cervical and lingual-apical regions in both groups were found to have significantly larger resorption volumes than other regions ( p < 0.005). These clinical observations are complemented by the FEA results, suggesting that root resorption was more likely to occur when the volume average compressive hydrostatic pressure exceeded the capillary blood pressure (4.7 kPa).

J Mech Behav Biomed Mater ; 89: 150-161, 2019 01.
Artigo em Inglês | MEDLINE | ID: mdl-30286374


OBJECTIVES: This study aimed to develop a simple and efficient numerical modeling approach for characterizing strain and total strain energy in bone scaffolds implanted in patient-specific anatomical sites. MATERIALS AND METHODS: A simplified homogenization technique was developed to substitute a detailed scaffold model with the same size and equivalent orthotropic material properties. The effectiveness of the proposed modeling approach was compared with two other common homogenization methods based on periodic boundary conditions and the Hills-energy theorem. Moreover, experimental digital image correlation (DIC) measurements of full-field surface strain were conducted to validate the numerical results. RESULTS: The newly proposed simplified homogenization approach allowed for fairly accurate prediction of strain and total strain energy in tissue scaffolds implanted in a large femur mid-shaft bone defect subjected to a simulated in-vivo loading condition. The maximum discrepancy between the total strain energy obtained from the simplified homogenization approach and the one obtained from detailed porous scaffolds was 8.8%. Moreover, the proposed modeling technique could significantly reduce the computational cost (by about 300 times) required for simulating an in-vivo bone scaffolding scenario as the required degrees of freedom (DoF) was reduced from about 26 million for a detailed porous scaffold to only 90,000 for the homogenized solid counterpart in the analysis. CONCLUSIONS: The simplified homogenization approach has been validated by correlation with the experimental DIC measurements. It is fairly efficient and comparable with some other common homogenization techniques in terms of accuracy. The proposed method is implicating to different clinical applications, such as the optimal selection of patient-specific fixation plates and screw system.

Osso e Ossos/citologia , Análise de Elementos Finitos , Estresse Mecânico , Tecidos Suporte , Fenômenos Biomecânicos , Fêmur/citologia , Modelos Biológicos , Porosidade
IEEE Trans Biomed Eng ; 63(1): 188-98, 2016 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-26415146


GOAL: To validate a new electroanatomical model of the implanted guinea pig cochlea against independently obtained in vivo voltage tomography data, and evaluate the validity of exist-ing modeling assumptions on current paths and neural excitation. METHODS: An in silico model was generated from sTSLIM images and analyzed in COMSOL Multiphysics. Tissue resistivities and boundary conditions were varied to test model sensitivity. RESULTS: The simulation was most sensitive to the resistivities of bone, perilymph, and nerve. Bone tissue in particular should be separated by morphology because different types of bone have different electrical properties. Despite having a strong impact on intrascalar voltages and exit pathways, most boundary conditions, including a new alternative proposed to account for the unmodeled return path, only had a weak effect on neural excitation. CONCLUSION: The new model demonstrated a strong correlation with the in vivo voltage data. SIGNIFICANCE: These findings address a long-standing knowledge gap about appropriate boundary conditions, and will help to promote wider acceptance of insights from computational models of the cochlea.

Cóclea/fisiologia , Implantes Cocleares , Simulação por Computador , Estimulação Elétrica/métodos , Processamento de Imagem Assistida por Computador/métodos , Animais , Análise de Elementos Finitos , Cobaias , Reprodutibilidade dos Testes
IEEE Trans Biomed Eng ; 62(2): 728-35, 2015 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-25347872


The current conduction pathways resulting from monopolar stimulation of the cochlear implant were studied by developing a human electroanatomical total head reconstruction (namely, HEATHER). HEATHER was created from serially sectioned images of the female Visible Human Project dataset to encompass a total of 12 different tissues, and included computer-aided design geometries of the cochlear implant. Since existing methods were unable to generate the required complexity for HEATHER, a new modeling workflow was proposed. The results of the finite-element analysis agree with the literature, showing that the injected current exits the cochlea via the modiolus (14%), the basal end of the cochlea (22%), and through the cochlear walls (64%). It was also found that, once leaving the cochlea, the current travels to the implant body via the cranial cavity or scalp. The modeling workflow proved to be robust and flexible, allowing for meshes to be generated with substantial user control. Furthermore, the workflow could easily be employed to create realistic anatomical models of the human head for different bioelectric applications, such as deep brain stimulation, electroencephalography, and other biophysical phenomena.

Encéfalo/fisiologia , Cóclea/fisiologia , Implantes Cocleares , Cabeça/fisiologia , Modelos Biológicos , Adulto , Simulação por Computador , Campos Eletromagnéticos , Feminino , Humanos , Espalhamento de Radiação , Software
Conf Proc IEEE Eng Med Biol Soc ; 2013: 5291-4, 2013.
Artigo em Inglês | MEDLINE | ID: mdl-24110930


It is known that the inclusion of blood vessels in finite element (FE) models can influence the current conduction results. However, there have been no studies exploring the impact of blood vessel conductivity on human head models for cochlear implant (CI) stimulation. The three-dimensional (3D) FE model presented in this paper aims to provide understanding in this regard. The electrical conductivity of blood was varied to determine the sensitivity of the 3D model. The results show that some of the current is exiting the cochlea and taking the jugular vein pathway. When compared to the case with blood vessels being omitted, the current density in the blood increased by 13.1%, 17.2% and 20.7% for low, medium and high electrical conductivity cases considered, respectively. This study suggests that blood vessels cannot be neglected from CI models as the jugular vein can provide a low impedance pathway, through which current can leave the cochlea. It also indicates the importance of using correct tissue property values for performing accurate bioelectric modeling analyses.

Vasos Sanguíneos/fisiologia , Implantes Cocleares , Condutividade Elétrica , Análise de Elementos Finitos , Modelos Biológicos , Cóclea/anatomia & histologia , Cóclea/fisiologia , Implante Coclear , Estimulação Elétrica , Feminino , Cabeça , Humanos
Conf Proc IEEE Eng Med Biol Soc ; 2013: 1554-7, 2013.
Artigo em Inglês | MEDLINE | ID: mdl-24109997


Most neural prostheses feature metallic electrodes to act as an interface between the device and the physiological tissue. When charge is injected through these electrodes, potentially harmful reactions may result. Others have developed finite element models to evaluate the performance of stimulating electrodes in vivo. Few however, model an electrode-electrolyte interface, and many do not address electrode corrosion and safety concerns with respect to irreversible reactions. In this work, we successfully develop a time domain finite element model of cochlear implant electrodes that incorporate oxygen reduction and platinum oxidation reactions. We find that when electrodes are stimulated with current pulses (0.5 mA, 25 µs), faradaic reactions may cause an increase in the peripheral enhancement of the current density.

Implantes Cocleares , Eletroquímica/métodos , Análise de Elementos Finitos , Modelos Teóricos , Implante Coclear , Eletricidade , Eletrodos , Fatores de Tempo