Luis Héctor Hernández-Gómez

Assessment of the Structural Integrity of C3–C5 Cervical Porcine Vertebrae Model Based on 2D Classic CAD, 3D Scanner and 3D Computed Tomography

In this chapter, the biomechanical behavior of C3–C5 porcine cervical vertebrae is analyzed. The objective of this evaluation is to establish the advantages and limitations of three numerical procedures when a compressive load is applied. In a first stage, a damaged C4 vertebral body is instrumented with a bone graft and a titanium alloy (Ti-6A1-4V) cervical plate fixed with titanium alloy screws. In the second stage, the biomechanical integrity of a healthy C3–C5 unit is studied. The required numerical models were created with three different techniques; these are 2D Computer Tomography (CT), 3D ZScan and CT scanning with a Siemens Emotion system. This was done in conjunction with Pro-E Wildfire 4.0, Scan IP 3.1, UGS NX-4 and Geomagics R 10 codes. Lateral displacements among the upper and lower surfaces of the vertebral bodies and the bone graft, as well as the von Misses stresses, were calculated. Numerical differences from the biomechanical models are discussed. In order to establish a performance criterion, the results obtained were compared against those obtained for the case of the instrumented C3–C5 unit. In order to establish helpful criteria to optimize the therapeutic procedures before a surgery is performed, the analysis of the results was focused to demonstrate that DICOM methodology can be applied when a biomechanical simulation for a patient is required. It is possible, to apply this technique safely as it is not invasive and geometrical parameters are obtained directly from a tomography taken at a hospital. On the other hand, classical CAD models and Z scan methodology has shown to be useful when specimens are numerically analyzed.

Biomechanical Characterization of a Cervical Corporectomy using Porcine Specimens, following an Experimental Approach

In this paper, the interaction among cervical vertebrae, a cervical plate and a bone graft implant, which is developed in a Corporectomy, is analyzed in an experimental form. In the case of specific damaged vertebra, its replacement is one of the alternative solutions. However, the displacement between the vertebral adjacent facets and the bone graft is a critical parameter which has to be evaluated in order to ensure the stability of the spine. Besides, it is advisable to make a precise evaluation of the structural integrity of the arrangement. For this study, porcine cervical vertebrae (C3-C5) were instrumented in order to replace a damaged C4 vertebra. This arrangement was tested under compression. The experimental observations were complemented with a numerical model. The displacements between the vertebral facets and the bone graft were measured. They are lower than 3 mm in order to develop stability in the spine. Besides, the proposed arrangement has structural integrity and the surgical procedure is simplified, as no wires are used.

Biomechanics and Numerical Evaluation of Cervical Porcine Models Considering Compressive Loads Using 2-D Classic Computer Tomography CT, 3-D Scanner and 3 -D Computed Tomography

In this paper the biomechanical behavior and numerical evaluation results of three C3-C5 porcine cervical models created with different modeling techniques are shown. The objective of this evaluation is to know the differences between the biomechanical effects on a bone graft, which replaces a damaged C4 vertebral body, a titanium alloy (Ti-6A1-4V) cervical plate, used to isolate the C4 damaged vertebra, and the influence on the compressive loads on the complete and instrumented C3-C5 cervical model. The biomechanical integrity of the healthy C3 and C5 vertebral body after the fixation of the cervical plate using titanium alloy screws is considered. Besides, 2-D Computer Tomography classic technique, 3-D Scanner Z-Corp 700 and a CT scanning Philips Brilliance system was used to create the three FEM models. In addition, 3-D Software as Pro-E Wildfire 4.0, ScanIP 3.1, UGS NX-4 and Geomagics R 10.0 was used to create specific numerical model. Main displacements and von Misses stresses between the upper and lower surfaces of the vertebral bodies and the bone graft and the influence of the titanium alloy (Ti-6A1-4V) screws on the vertebral body of C3 and C5 were evaluated. The contribution of this study is to optimize the actual surgical technique once the numerical results on the FEM model have been analyzed. In other words, the numerical disparity between classic CT techniques versus 3-D modern techniques is established.

Locating Defects Using Dynamic Strain Analysis and Artificial Neural Networks

An inverse artificial neural network (ANN) assessment for locating defects in bars with or without notches is presented in the paper. Postulated void defects of 1mm x 1mm were introduced into bars that were impacted with an impulse step load; the resultant elastic waves propagate impinging on the defects. The resultant transient strain field was analyzed using the finite element method. Transient strain data was collected at nodal points or sensors locations on the boundary of the bars and used to train and assess ANNs. The paper demonstrates quantitatively, the effects of features such as the design of ANN, sensing parameters such as number of data collection points, and the effect of geometric features such as notches in the bars.

Modelling of a Cervical Plate and Human Cervical Section C3 – C5 under Compression Loading Conditions Using the Finite Element Method

This paper presents the modelling of the effects due to load conditions on the cervical section defined between C3 and C5 after a cervical plate implant is used to transfer the compression loads from C3 to C5 as C4 is considered to be damaged as a result of a medical condition. For this study, three different scenarios which describe the common motion condition of the head-neck system are modelled. The first one refers to the effect of the head weight over the considered section. In the second case the average patient weight is supported by C3 and C5 vertebrae. The last case simulates extreme loading conditions as vertebrae lesions occur when these are compressed beyond its failure limit; the ultimate stress to compression load failure value is applied to C3. The stability and mechanical behaviour of cervical plates under compression loading conditions is evaluated using the Finite Element Method (FEM). Cervical plates are useful to restore stability of the spine by improving the inter-vertebral fusion, particularly when the cervical body has been damaged. The results show that the stresses on the plate and fixation screws, for the three cases, are within the elastic range. Conversely, it has to be considered that cortical and trabecular bone densities vary from one patient to another due to a number of factors, which can influence the fixation conditions of the screws. In the case of this analysis, healthy bone conditions were considered and the obtained results show that the risk of the integrity of the screwimplant- vertebrae system is not compromised.

Evaluation of crack propagation stability with the williams stress function—I. Stress field analysis

The influence of the value of the second coefficient of the Williams stress function on the crack propagation stability is studied. The conclusions obtained established that the second coefficient determines crack stability. Accordingly, the program ANGCRK is validated and used for the numerical evaluation of crack propagation stability. An extension of this study to the case of two dimension edge-cracked specimens loaded with biaxial load is made in a companion paper.

Assessment of data for dynamic crack initiation under shock pressure loading: Part I—experiment

Abstract A technique for analyzing crack initiation and growth in polymeric materials is described. The specimen is a circular plate fixed at the edge and subjected to a pressure shock wave loading. The design of the test is shown to reflect the loading history. Static tests can also be performed with the same equipment. The results of both static and dynamic tests are compared in terms of the load intensity required for crack initiation. It is found that this is higher for the static tests than for the dynamic tests, as expected.

Synthesis Optimization of Planar Mechanisms

This work presents an approach based on Genetic Algorithms (GA) for the dimensional synthesis of planar mechanisms as path generators. The study case deals with the development of a four-bar mechanism with application to lower limb prosthesis, specifically the knee joint. The optimization algorithm contains the objective function defined by the synthesis problem and the representation of a set of mathematical relationships that describe the kinematic restrictions of the planar mechanism. The objective function is a given numerical value for every solution that corresponds to the best possible mechanism. In other words, this objective function is the determinant to minimize the error between the desired and the generated points and can be affected by the lengths of the links, the transmission angles, the Grashof conditions, type of mechanisms, etc. The population, crossover or mutation in the GA determines the exactitude in the results. The first goal of this work is to find the optimal dimensions of the links to minimize the error between the actual coupler curve and the desired path.

Bidirectional optical Kerr transmittance in a bilayer nanocomposite with Au nanoparticles and carbon nanotubes

Experimental and numerical results about the propagation of optical signals in a bidirectional two-wave mixing system with Au nanocomposites and carbon nanotubes are presented. Au nanoparticles embedded in a TiO2 thin solid film were prepared by a sol–gel processing route; while carbon nanotubes were obtained by a thermal decomposition approach. A thin film conformed by carbon nanotubes was put on top of the Au nanocomposites for the nonlinear optical measurements. A two-wave mixing experiment was conducted to distinguish the direction of propagation of a probe-beam through the exploration of an induced birefringence and two-photon absorption. The third-order nonlinear optical response of the sample was evaluated by considering discrete groups of energy numerically modeled by the beam propagation method. Remarkable differences exhibited by the propagation and counter-propagation of a polarized probe beam were identified by nanosecond pulses at 532 nm wavelength. By employing a 405 nm wavelength as a probe beam, we were able to change the behavior of the direction of maximum Kerr transmittance in a particular geometry of a non-degenerated multi-wave system. It can be contemplated that the influence of distinctive near- and off-resonant excitations of the samples seems to be useful to control a selective one-way transmittance with potential applications for developing all-optical systems.

Optimization of the Design of a Four Bar Mechanism for a Lower Limb Prosthesis Using the Taboo Search Algorithm

In this chapter, the optimization of the design of a four bar mechanism used in polycentric prosthesis with voluntary control is reported. This prosthesis has been used by a male, whose left leg was amputated above the knee. He is 34 years old, weighs 78 kg and is 1.75 m tall. One of the objectives of this optimization was to fulfill the requirements of his anthropometric characteristics. The taboo search algorithm was used for this purpose. In this case, the lengths of the links were determined, following an inverse analysis. The objective function was the minimization of the error between the target trajectory of the instantaneous center of rotation (ICR) and the path followed by ICR of the four bar mechanism. This curve is very important because it is related with the kinematic and the forces that are developed in the gait cycle. Therefore, it is expected that the amputee individual develop a natural gait cycle with this prosthesis. In the final stage, 1,900 iterations were carried out and the lengths of the bars were augmented by 0.01 mm. The lengths of the links of the optimized mechanism are the following: Bar 1 = 43 mm; Bar 2 = 55.5 mm; Bar 3 = 59 mm and Bar 4 = 29 mm. With this information, the prosthesis was manufactured and adapted to the patient.