Compressive properties of the whole TMJ disc

In this study, the dynamic and static compressive properties of the whole porcine temporomandibular joint (TMJ) disc were investigated. The aim of the study was to develop a new simple method for the evaluation of joint viscoelasticity, enabling examination of the load-bearing capacity and joint flexibility of the entire disc. For the experiments, a novel testing fixture that reproduces the condylar and fossa surfaces of the TMJ was developed to replicate TMJ disc geometry. Ten porcine discs were used in the experiments. Each disc was dissected from the TMJ and sinusoidal compressive strain was applied to obtain the storage and loss moduli. Static strain control tests were carried out to obtain the relaxation modulus. The result of static and dynamic tests indicated that the whole disc presented viscoelastic behavior under compression. Storage and loss moduli increased with frequency and the relaxation modulus decreased over time. The loss tangent showed less frequency dependence, with values ranging from 0.2 to 0.3, suggesting that the viscous properties of the disc cannot be neglected. These results provide a better understanding of whole disc mechanical compression behavior under realistic TMJ working conditions

Characterization and Assessment of Mechanical Properties of Adipose Derived Breast Tissue Scaffolds as a Means for Breast Reconstructive Purposes

Decellularized adipose tissue (DAT) has shown great potential for use as a regenerative scaffold in breast reconstruction following mastectomies or lumpectomies. Mechanical properties of such scaffolds are of great importance in order to mimic natural adipose tissue. This study focuses on the characterization of mechanical properties and assessment of DAT scaffolds for implantation into a human breast. DAT samples sourced from multiple adipose tissue depots within the body were tested and their elastic and hyperelastic parameters were obtained. Subsequently simulations were conducted where the calculated hyperelastic parameters were tested as a real human breast model under two different gravity loading situations (prone-to-supine, and prone-to-upright positions). DAT samples were also modelled for post-mastectomy, and post-lumpectomy reconstruction purposes. Results show that DAT shows similar deformability to that of native tissue, and varying DAT depots exhibited little intrinsic nonlinearity. Finally, contour defects were not observed for the samples under either loading conditions

Efficient isogeometric thin shell formulations for soft biological materials

This paper presents three different constitutive approaches to model thin rotation-free shells based on the Kirchhoff-Love hypothesis. One approach is based on numerical integration through the shell thickness while the other two approaches do not need any numerical integration and so they are computationally more efficient. The formulation is designed for large deformations and allows for geometrical and material nonlinearities, which makes it very suitable for the modeling of soft tissues. Furthermore, six different isotropic and anisotropic material models, which are commonly used to model soft biological materials, are examined for the three proposed constitutive approaches. Following an isogeometric approach, NURBS-based finite elements are used for the discretization of the shell surface. Several numerical examples are investigated to demonstrate the capabilities of the formulation. Those include the contact simulation during balloon angioplasty.Comment: Typos are removed. Remark 3.4 is added. Eq. (18) in the previous version is removed. Thus, the equations get renumbered. Example 5.5 is updated. Minor typos in Eqs. (17), (80), (145) and (146), are corrected. They do not affect the result

FINITE ELEMENT MODELING OF ICD LEAD SILICONE SOFT-TIPS

Although highly underutilized by the medical device industry, Finite Element Analysis (FEA) in the development of new technologies is gaining popularity as regulatory bodies such as the Food and Drug Administration (FDA) begin to require additional proof of safety through scientific methods. Non-linear FEA allows engineers to realistically simulate the mechanical behavior of implants as seen in the in-vitro, or in some cases, the in-vivo configurations. The work presented in this report investigates how computational methods can be used to simulate the interaction of a St. Jude Medical silicone soft-tip as it passes through a Peel-Away Sheath (i.e. introducer). In this analysis the soft-tips were modeled as axisymmetric with hyperelastic material properties assigned to the soft-tips. An Ogden, second order hyperelastic material model was used to describe the non-linear stress-strain behavior of silicone soft-tips. The finite element program, ABAQUS/Standard was used to simulate the soft-tip/introducer interactions. The reaction forces obtained through these simulations represent the force required to push a lead through an introducer, and were then compared to experimental data

Finite Element Analysis Simulating Indentation Testing of Human Vaginal Tissue

Finite element analysis has often been used in conjunction with experimental testing to provide in-depth understanding of material properties. The aim of this study was to develop a finite element model to be utilized for the interpretation of indentation testing on human, in vivo vaginal tissue. Two distinct models were explored to understand the mechanical material properties and the dynamic influences. First, a single layer, flat tissue model was evaluated. Small indentation simulation was performed to validate the model according to Hertz theory of elasticity. Once validated for multiple elastic moduli, large deformation was applied. Stress and strain along with force were investigated in relation to the displacement of the indenter into the tissue and the Young’s modulus. Next, the findings of the single layer simulation were compared against preliminary, experimental, indentation, test results. Force-displacement results were assessed. Although fundamental differences including geometric and process variances lead to non-congruent results, highly valuable information was attained including understanding of extreme limits that may be found during in vivo experimentation. Finally, a second model was developed based on the findings of the first single-layer model. This new model incorporated multiple tissue layers for the investigation of influence of adjacent tissue properties on vaginal tissue properties during compression testing. Interpretations of each model were then discussed and conclusions drawn regarding how changes in the properties provide further understanding of tissue dynamics. Further discussion was also provided on possible changes to enhance the model

Brain Tissue Response Analysis Based on Several Hyperelastic Models, for Traumatic Brain Injury Assessment

Abstract Numerous geometrically simplified models may be found in literature for simulation of the traumatic brain injuries due to the increased intracranial pressure caused by sever translational accelerations of the brain inside the cranium following the impact waves. Some researchers have used more accurate models but employed specific hyperelastic material models. No research has presented a comprehensive comparison among results of various geometric and hyperelasticity models, so far. In the present research, two distinct finite element models and four hyperelastic constitutive models (i.e., polynomial, Yeoh, Arruda-Boyce, and Ogden models) are employed to accomplish the mentioned task. Therefore, the motivation is checking accuracy of the modeling procedure and discussing the results according the traumatic brain injury criteria. In this regard, a realistic skull-brain model is reconstructed in CATIA software based on the MRI scans and employed for optimized mesh generation in HYPERMESH finite element software. Influence of the contact and nonlinear characteristics of the brain tissue are considered in simulation of the relative motions in LS-DYNA finite element code. Time histories of the accelerations and the pressures (von Mises stresses) are derived from ANSYS finite element analysis code. Finally, the responses are discussed based on the available traumatic brain injury criteria and tolerances. Comparisons made with the available experimental results for the four hyperelastic constitutive equations confirm that employing Arruda-Boyce or Ogden models may lead to inaccurate or even erroneous results. On the other hand, the polynomial model is the most accurate model but underestimates the injury probability and may be used with care

Acquiring Uniaxial Stress-Strain Curve by Fast Finite Element Analysis for Characterization of Whole-Cell Elastic Property

An understanding of whole-cell elastic property can provide insight into cellular response to mechanical loading. Hertz model is often used to extract the Young’s modulus from the atomic force microscopy (AFM) force indentation depth curve (F-D curve) for characterization of cell’s elastic property. However, Hertz model is only relatively accurate when the sample can be regarded as infinite half space and its material is linear elastic, which is contradictory with the fact that cell is usually very thin and cell’s elastic properties are considered to be highly nonlinear, especially when the deformation is very large. Finite element analysis can be used to handle the nonlinear elastic property and large deformation by using the hyperelastic model to model the cell material. However, previous studies have not demonstrated a convenient way to search for the model parameters that can fit the experimental data. In this paper, we put forward a method based on finite element analysis. Our new method adopts a general uniaxial stress-strain curve (associated with a hyperelastic model) to represent cell’s material and uses a recursive method to search for this uniaxial stress-strain curve by minimizing the difference between the experimental and simulated F-D curve. This new recursive approach not only offers a high match accuracy between the experimental and simulated F-D curve(error rate less than 5% is ready to be obtainable), but also minimizes the number of recursions in searching for the stress-strain curve(less than 10 recursions are enough for the good enough match in normal situation)

Measurement of the Hyperelastic Properties of Ex Vivo Breast Tissue Slices

The elastic and hyperelastic properties of biological soft tissues have been of interest to the medical community as there are several applications where parameters characterizing these properties are critical for a reliable clinical outcome. This includes applications such as surgery planning, needle biopsy, and cancer diagnosis using medical imaging. While there has been considerable research on the measurement of the linear elastic modulus of small tissue samples, little research has been conducted for measuring parameters that characterize non-linear elasticity of tissues included in slice specimens. In this work a method for measuring the hyperelastic parameters of tissue slice samples with tumours is presented. In this method, to measure the hyperelastic properties of a tumour within a slice sample, the tumour was indented to acquire its force-displacement response while the slice remained intact. To calculate the hyperelastic parameters from the acquired data, two inversion techniques were developed that use the slice nonlinear finite element model as their forward problem solver. One of these techniques was based on nonlinear optimization while the other is a novel iterative technique that processes the variable slopes ofthe force-displacement response to calculate the hyperelastic parameters. The latter was developed specifically for the Yeoh and the second order Polynomial hyperelastic model, since it was found that the other optimization based inversion technique did not perform well with these models. To validate the proposed techniques, numerical and phantom experiments were performed. Convergence with wide ranges of parameters of initial guesses was achieved, to within 1% error with the numerical simulation experiments, and also with errors of around 5-10% with the tissue mimicking phantoms. Moreover, these techniques were successfully applied to data that was acquired from 44 pathological breast tissue slice specimens where the goal was to determine the hyperelastic properties of the tumour within the breast tissue slices. A statistical analysis was performed in an attempt to correlate specific hyperelastic propertiestotissuepathology. Itwasconcludedthatfurtherresearchisrequiredto ascertain the reliability of using a hyperelastic parameter for cancer classification. It was also concluded that, based on the available data, it may be difficult to identify specific pathologies based solely on individual hyperelastic parameters and that a consideration of the entire parameter set may be necessary and that factors other than tissue pathology may be involved in tissue stifftιess, such as age