Guillermo Urriolagoitia-Sosa

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.

Identification of inhomogenous optical absorptive response by chaotic photonic signals in Au nanoparticles

A chaotic circuit allows us to identify with a high sensitivity the optical absorption associated with a highly transparent sample with Au nanoparticles embedded in a TiO2?thin film prepared by a sol?gel method. The measurements are based on a comparison of the correlation between a controlled optical irradiance that propagates through different zones of the sample. Nanosecond nonlinear optical measurements were obtained by monitoring the transmittance and the amplitude modification for the vectorial components of the electric fields in a two-wave mixing interaction. In addition, we theoretically study chaotic physical behavior exhibited by optical signals under nonlinear optical absorption. Our numerical results point out that small intensity fluctuations related to excitations of the absorptive nonlinearity can be described using a simple fractal model. Potential applications for developing sensors and instrumentation of the optical response of advanced materials are contemplated.

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.

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.

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.

Biomechanical evaluation of a corporectomy in porcine lumbar specimens using flexible polymer belts

This paper presents the experimental results of a biomechanical evaluation in lumbar porcine specimens (L2–L4), instrumented with flexible polymer belts, under fatigue and tensile loading. The clinical effect called facetary arthrosis is evaluated. An experimental analysis was carried on 3 lumbar porcine specimens. In two of them, polyamide belts are fixed on the interspinous ligament from L2 to L4. Specimens are taken from pigs which are 6 month old. For the present work, the stiffness reduction of the spine and the biomechanical behaviour of the belts in conjunction with the interspinous ligament are evaluated. The purpose is to determine the failure conditions for the elements of the specimen (vertebral disk, supra and intraspinous ligament and vertebral body). Under static loading, which is the base line case, the elements of the specimen failed as a typical healthy structure. While in the fatigue combined with static loading, the element failed in different order. Additionally, the stiffness changed in accordance with the fatigue loading conditions. Because of the simplicity of this alternative technique, a high level of the structural integrity is preserved, as no holes are made on the spinous process in order to insert the fixation screws. Furthermore, there is a cost reduction.

Performance Optimization of GA Based Planar Mechanism Synthesis

This paper present the analysis of the manipulation of some parameters to improve the performance of genetic algorithm based planar mechanism synthesis, such as the mutation and crossover probability and the population size, applied to a specific case of dimensional optimization, to obtain the best results for a group of design variables that achieve the best performance in the design of planar mechanisms, whose evaluation is expressed by means of an objective function that has to meet certain restrictions or requirements to minimize the error between the desired and generated trajectory of the coupler link, since the objective of path generation is to find the mechanism that properly describes the desired curve in shape, size, orientation and position. Two examples are given for illustration, for which the mentioned parameters are manipulated to see the effects of these on the final result for the minimization of the error and the value of variables involved in the dimensions of the links and the motion angles.

Numerical and experimental evaluation of the residual stress relaxation and the influence zone due to application of the crack compliance method

This paper presents the results concerning an evaluation of the crack compliance method. The research was focused on the relaxation caused by a cut induced to obtain the data required to calculate the residual stress field. The main objective in this research is to establish the optimum place to cut in a specimen that has suffered a failure and how extended is the zone of relaxed stresses. It has been recognized that a crack vanishes the beneficial or detrimental effects of the residual stress fields. This research has been performed in a numerical and experimental way, so results can be compared and FEM on this topic can be assessed.

Numerical Evaluation of the Crack Compliance Method (CCM) in Beams with and without Prior History

This work assesses the Crack Compliance Method (CCM), which has been extensively used for the experimental evaluation of residual stresses, by the Finite Element Method (FEM) to validate its experimental applicability through numerical evaluation. The CCM is a very powerful method that is based on Fracture Mechanics theory, but its experimental application and set up has not been totally scientifically validated. In this paper, a numerical evaluation is presented on the basic applications of the CCM. The assessment of the CCM is performed on bending beams with and without prior straining history. To determine the best position and orientation of the strain gages, as well as the optimum number of readings, a number of numerical simulations where also performed for the correct performance of the experimental evaluation of the CCM. The prior straining history condition, in the analyzed components, is induced by an axial pulling before the beam is bent. Three levels of preloading are considered: low, medium and high (which are related to the yield strain of the simulated material); Isotropic and Kinematic hardening rules are also considered. After the residual stress field is induced by bending, a slot cutting is simulated and the strain relaxation produced is captured, which is used later in the CCM program for the quantification of the original residual stress field. The results obtained in this work, provide a quantitative demonstration of the effect of hardening strain on the distribution of the residual stress in beams. In the same manner, the theoretical formulation of the CCM has been evaluated validating the application of this method for the determination of residual stress fields in mechanical components.