Guillermo Urriolagoitia-Calderón

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.

Mechano-optical modulation and optical limiting by multiwall carbon nanotubes

An optical limiting effect in multiwall carbon nanotubes was modulated by using a two-wave mixing experiment assisted with a mechanical actuator. We employed a 532 nm wavelength and 1 ns pulse duration for exciting the nonlinear optical absorption. The nanotubes were prepared by an aerosol pyrolysis method. The resulting samples were deposited on a pure silica substrate as an inhomogeneous thin film. The mechano-optical modulation was obtained by the orthogonal rotation of the sample with respect to the probe beam. In addition, low-irradiance patterns provided by a Michelson optical interferometer allowed us to comparatively corroborate the mechano-optical effect induced by the rotation of the film.

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.

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.

Numerical Study in Biomodels of Maxillofacial Prosthesis (Cancer and Osteonecrosis Cases)

This work shows a methodology to successfully generate an anatomically appropriate mandibular prosthesis for two patients with different conditions affecting the bone: cancer and necrosis. A common technique for bio-modeling was used in both cases, which includes tomographic slices of 0.5 mm for each clinical case. As a result of the processing a stereolithographic model was performed using two different techniques, were the affected area was reconstructed. In the osteonecrosis case, with the use of auxiliary guide paths and drawings in the CATIA platform a 3D model was produced, achieving a partial replacement with lateral support; while in the cancer case a left lateral replacement with the ramus was produced by reconstructing surfaces and patterns of the required area in PowerShape® and Solidworks® platforms. The region to replace was defined by the surgical expertise of a maxillofacial physician. Both cases were printed in acrylonitrile butadiene styrene (ABS) polymer producing a three-dimensional model, which was adjusted by the maxillofacial surgeon and subsequently integrated into a compound that includes cyanoacrylate with low toxicity, calcium powder, hydroxyapatite and isophthalic resin as a fundamental basis. The models were analyzed numerically using the same conditions that will be applied mechanically and clinically in order to obtain preliminary information on stress concentration zones and material deformation.