Analysis and Design of Biological Materials and Structures

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.

Stress distribution in the arterial wall has been shown to be associated with several vascular disease, e.g., atherosclerosis and abdominal aortic aneurysm (AAA). The variation of material properties of the vascular wall is related to the local onset of disease, which leads to the alterations of stresses and strains that provide essential clinical information. We therefore investigate the distributions of stresses and strains in a longitudinal, heterogeneous arterial wall under physiologic loadings. Four Models were analyzed: Model 1 was the idealized Young’s modulus for normal aorta, Model 2 was the idealized Young’s modulus for pathological aorta, Model 3 was the actual Young’s modulus for the normal aorta, and Model 4 was the actual pathological (AngiotensinII-treated) aorta. The arterial Models were assumed to have idealized geometry, i.e., axisymmetric, uniform, cylindrical, purely elastic. In Model 1, we assumed the wall material to be homogeneous, i.e., described by its Young’s modulus equal to 150 kPa. One stiff inclusion was defined at the middle part of Model 2, by changing its Young’s modulus 150–550–150 kPa. The local Young’s moduli, which are experimentally estimated from our previous study, in Model 3 and 4 were equal to 140.8 ± 10.2 and 1676.8 ± 926.0 kPa, respectively. Stress and strain calculations in all cases were performed using a finite-element method. The transmural stress and strain decreased toward the outer wall uniformly in Model 1, i.e., stress ratio was equal to 133.3%. But the stress dramatically increased at the boundary of stiff-soft region in Model 2, i.e., stress ratio was equal to 187.0%. While the trends of stresses and strains in Model 1 were uniform longitudinally, sharp-increases of stresses in Model 2 were found at the boundaries between high and low Young’s moduli, i.e., 25% higher of the adjacent sections. Model 3 and 4 have depicted similar stress and strain trends as Models 1 and 2. However, Model 3 is not perfectly homogeneous, and thus slight increases stress in axial direction, and an even higher number of such increases were found in Model 4. This is because of the longitudinal change in material properties that cause changes in the stress and strain distribution. These stress discontinuities may indicate a higher risk for rupture in the affected area. A feasibility study was thus shown for monitoring suspicious wall regions that may be more prone to disease due to their higher heterogeneity.

It is well known that the success of dental implants is heavily dependent on the initial stability and long-term osseointegration due to optimal stress distribution in the surrounding bones. This research describes a numerical study performed with the finite element method due to the commercial code, ABAQUS, of new dental implant system in order to know the effect of the elastomer material under an occlusal load on the equivalent von Mises interface stresses induced. These stresses were compared with the ones provoked by the standardized implant. The von Mises stress distribution indicated that the stress was maximal around the top of the implant with varying intensities in the different loading cases. The stress was highest in the cortical bone at the neck of the implant and lowest in the cancellous bone. Overall, the novel implant provoked lower interface stresses only in the cortical bone due to the stress shielding effect of the elastomeric stress barrier.

Bioceramics with reduced grin size below 100 nm have superior mechanical properties and more bioactivity than conventional ceramics. The aim of this work was to prepare and characterize a novel hydroxyapatite-forsterite-bioactive glass composite nanopowder. The novel hydroxyapatite-forsterite-bioactive glass composite nanopowder was fabricated by incorporation of forsterite and bioactive glass nanopowder in hydroxyapatite matrix via a sol–gel process. X-ray diffraction (XRD), scanning electron microscopy (SEM) and transition electron microscopy (TEM) techniques were utilized in order to determine the phase composition, and evaluate the morphology and particle size of the synthesized nanopowders. The effect of the sintering temperature was also investigated. The results show that the appropriate temperature for desired calcination was 600°C and that the particle size of the prepared composite nanopowder was about 60–70 nm. The obtained results suggest that the prepared composite nanopowder might be a good candidate for biomedical applications.

One of the most important issues in pediatric cardiac surgery is myocardial protection when a cardioplegic solution mixed with oxygenated blood is injected into coronary arteries with a pump. In this case, it is necessary to establish the right pressure of the cardioplegic solution in coronary arteries taking into account their biomechanical properties. Biomechanical properties of eight specimens of coronary arteries from neonates 12.3 ± 13.7 days old and weight 4.1 ± 0.9 kg were investigated and compared with adult arteries. Specimens were pressurized from 0 to 200 mmHg in steps of 20 mmHg while maintaining the length of the sample in situ. We observed that the relationship between stress and strain in neonates was non-linear. There was a rapid increase of strain until the inner pressure reaches 80–100 mmHg and not as rapid regarding to the stress in the arterial wall. When the internal pressure exceeds 100 mmHg the strain of the arterial wall increases much slower but at the same time the wall stress and modulus of elasticity begin to increase rapidly. It means that the structural elements of the arterial wall have been straightened and possible damage in the wall of coronary arteries of neonates may appear. These results were compared with biomechanical properties of arterial walls of adults and differences had been found. Our first experimental results show that the pressure of the cardioplegic solution in neonatal coronary arteries should not exceed 100 mmHg to decrease the risk of structural damage of the vascular wall.

The study to examine biomechanical properties of the aorta in neonates and the biomechanical properties of infantile aorta in case of different anastomoses used for surgical correction of aortic coarctation was started to detect the influence of the surgical technique on the biomechanics of infantile aorta and, therefore, the possible further changes in hemodynamics and blood flow. We analyzed seven specimens of native aorta and three specimens with the anastomosis end-to-end. We observed a non-linear relationship between stress and strain in the neonatal and infantile aorta. The strain of the end-to-end anastomosis was much smaller than in the native aorta. The modulus of elasticity of the aortic wall increased with the increase of inner pressure. However in the case of anastomosis end-to-end the modulus was almost constant and was relevant to the modulus of elasticity of the aorta with the inner pressure 100–120 mmHg. The results show that the stiffness of the anastomosis did not change with the changes in inner pressure which might affect hemodynamics.

Numerical studies of the blood flow system of aorta coronary sinus conduit were carried out using ANSYS™ CFD simulation. The pressure inside the conduit was investigated to ensure a pressure drop from 80 to 15 mmHg. It was aimed to model a coronary sinus conduit in three-dimension using ANSYS™ CFD. The simulation involved pre-modeling, modeling and simulation stages where the model will undergo each section of program in ANSYS™ CFD such as design modeler, meshing, pre-processing, solver and post-processing. From the analysis of coronary sinus conduit, it is found that a narrow tube needs to be incorporated into the conduit produce. This is to induce a venturi effect to reduce the pressure of blood from 80 to 15 mmHg within a specific throat length. A model of 3 mm inlet and throat diameter of 1.13 mm throat diameter show the best result for pressure reduction from 80 to 15 mmHg. The model gives a uniform pressure drop along the throat section of the conduit.

We developed a method to analyze aneurysm growth and rupture based on idealized spherical shape from actual patient-specific geometry data. This study was carried out to evaluate whether wall mechanics of soft tissue coupled with blood flow dynamics can be used to provide the insight into the weakening phenomena. In order to simulate the behavior of the system, the fluid structure interaction method (FSI) was utilized using transferred data from the fluid dynamics model to finite element wall mechanics. The FSI transferred these dynamics loads to exert the aneurysms wall whose respective deformations were then determined. The numerical modeling of aneurysms results the blood flow parameter of pressure and velocity inside the aneurysm sac in the form of profile correlations. These parameters generate a possible aneurysm rupture time during the growth as a reasonable quantitative observation. The developed method allows us to identify biomechanical factors that can influence the blood flow property changes and wall stress distributions. As part of the computed maximum wall stress to relate with growth and rupture, normalized velocity and pressure profiles inside the aneurysm sac were correlated. This explains the effect of blood flow to the weakening vessel wall and rupture behaviour due to variable flow conditions. These results assist medical practitioners to the prediction of time and location of ruptured aneurysm.

A generic method for keeping quality and quantity of fruits and vegetables named Modified Atmosphere Packaging is introduced. In this work, the interactions between respiration rates, permeability coefficients and headspace gas compositions are studied and the system is modeled mathematically. The dynamics of the system were solved using a fourth order Runge–Kutta method. A computer simulation package developed for analyses of mathematical aspects. Time to achieve equilibrium, equilibrium conditions and transient patterns compared under different permeation rates. A new performance index used as Integral of Time for Absolute Error (ITAE) based on dynamics of gas compositions to evaluate transient patterns for each gas. In this research, the permeability of some polymers from literature and theoretical packaging materials were studied and it was found that the behavior of each gas is different with others and the pattern of achieving the equilibrium depends on packaging permeability coefficients.

A kinetic model for biogas generation from banana stem waste was proposed on the basis of the obtained experimental results. The system consists of an anaerobic sequencing batch reactor for the first stage and an anaerobic fixed bed reactor for the second stage, which is operating at hydraulic retention times (HRT) of nine days. The process was conducted at ambient temperature for the first stage and thermophilic temperature for the second stage. Four differential equations described the overall process. This study employed first order kinetics for hydrolysis of non-soluble organic matter and a Michaelis–Menten equation type for the soluble organic matter decomposition, total volatile acids consumption and methane production. The following kinetics constants were obtained for the above-mentioned anaerobic stages: (a) hydrolysis and solubilization of organic matter: k₁ (kinetic constant for non-soluble organic matter degradation): 0.0037 day⁻¹; k₂ (maximum rate of soluble organic matter production): 0.0241 g soluble chemical oxygen demand (SCOD)/l day; k₃ (saturation constant): 0.0236 g SCOD/l; (b) acidogenesis: k₄ (maximum rate of soluble organic matter degradation): 0.0086 g SCOD/l day; k₅ (saturation constant): 0.0189 g SCOD/l; and (c) methanogenesis: k₆ (maximum rate of acetic acid (TVA) consumption): 0.0092 g TVA/l day; and k₇ (saturation constant): 0.0003 g TVA/l. The kinetic constants obtained and the proposed equations were used to simulate the different steps of the anaerobic digestion process of banana stem waste and to obtain the theoretical values of non-soluble and soluble CODs, TVA and methane production.

This work is a review of the mechanism of refraction in the human eye, to understand the deterioration of visual acuity. It is the conclusion of a work to 10 years for recovery of the presbyopia by the first author of this chapter doing physical exercises with the extra-ocular and ciliary muscle. It was Scheiner in 1619 apud (Werner et al. Arquivos Brasileiros de Oftalmologia, São Paulo, Brasil 2000), who proved in his experiments, made with holes in a card, in which an object is seen in each direction at a different distance. This corresponds to say that the person sees an object as projection images multiple superimposed in different positions on the retina, then, characterizes the effect resulting from the formation of lenses, originating from the clustering of metabolic secretions trapped in the cornea or lens without any organization. Through software, it is simulated the monocular vision of an object perceived by a patient, under the effect of metabolic secretions. The simulated object can be produced by a light source or the refraction of light, which causes different effects. In the image simulation of a text written by a pencil, on a lined paper, produced by the reflection of light, the text is erased and only the guidelines are displayed, as could happen with a person. It is shown, for monocular vision, the formation mechanism of the myopia, hyperopia, astigmatism and presbyopia due to the accumulation of metabolic secretions in the cornea or lens, and for binocular vision, it is justified the possibility of an individual having photosensitive epilepsy due to error refraction stimulated by colored beams and variable intensity emitted by television.

This work presents a kinematic and motion planning analysis for human gait simulation using a mechatronic model. The forward and inverse kinematics for calculating either positions or rotations of the lower member segments is based on collected data from a walking person. The trajectories are reconstructed using spline interpolation from the most representative motion points during gait in order to define different parameterized positions for each articulation. Both kinematics and motion planning allow obtaining suitable data for testing the mechatronic model which is designed considering direct current motors as muscle actuators for the knee and waist joints. Cylindrical objects are used for representing the thigh and shank along with their configured mechanical properties. Finally, through the use of Matlab \(^{\circledR} SimMechanics^{\rm TM}\) toolbox, interactions and dynamics between the lower member mechanism and the ground were simulated with motion captured data and experimental data from motion planning calculations. The motion planning results suggested that statistical data lead to gait paths not suitable for reproducing on a person, as each joint position does not match the subject’s real one. The simulation results from \(SimMechanics^{\rm TM}\)model, suggested that further components have to be considered in order to obtain more accurate trajectories thus, minimizing the error when comparing the obtained path with the motion captured data.