Tongtong Guo

Some factors that affect the comparison between isotropic and orthotropic inhomogeneous finite element material models of femur

The objective of this study was to investigate whether there were significant differences between isotropic and orthotropic inhomogeneous material models of femur by taking into account the effects of some factors, such as comparative parameters, loading conditions and mesh refinement. Three femoral meshes of increasing refinement levels were assigned isotropic and orthotropic material properties. Then six different loading conditions were separately applied to each material model. Based on the analysis results of Von Mises stress and nodal displacement, eight regions of interest in femur were selected to compare the differences between isotropic and orthotropic material models. The results showed that marked differences for Von Mises stress (maximum 13.25%) and nodal displacement (maximum 15.04%) appeared in the regions where the maximum absolute Von Mises stress and the maximum absolute nodal displacement did not occur. It was observed that the comparison results were significantly different under different loading cases. The mesh refinement had a great influence on the comparison results, especially for the Von Mises stresses in the regions of the femoral neck. Therefore, it can be concluded that the differences between two material property assignments are significant, at least in some local regions.

Effects of Materials of Cementless Femoral Stem on the Functional Adaptation of Bone

The objective of this paper is to identify the effects of materials of cementless femoral stem on the functional adaptive behaviors of bone. The remodeling behaviors of a two-dimensional simplified model of cementless hip prosthesis with stiff stem, flexible ‘iso-elastic’ stem, one-dimensional Functionally Graded Material (FGM) stem and two-dimensional FGM stem for the period of four years after prosthesis replacement were quantified by incorporating the bone remodeling algorithm with finite element analysis. The distributions of bone density, von Mises stress, and interface shear stress were obtained. The results show that two-dimensional FGM stem may produce more mechanical stimuli and more uniform interface shear stress compared with the stems made of other materials, thus the host bone is well preserved. Accordingly, the two-dimensional FGM stem is an appropriate femoral implant from a biomechanical point of view. The numerical simulation in this paper can provide a quantitative computational paradigm for the changes of bone morphology caused by implants, which can help to improve the design of implant to reduce stress shielding and the risk of bone-prosthesis interface failure.

Strain distribution of repaired articular cartilage defects by tissue engineering under compression loading

BackgroundIt is difficult to repair cartilage damage when cartilage undergoes trauma or degeneration. Cartilage tissue engineering is an ideal treatment method to repair cartilage defects, but at present, there are still some uncertainties to be researched in cartilage tissue engineering including the mechanical properties of the repaired region.MethodsIn this study, using an agarose gel as artificial cartilage implanted into the cartilage defect and gluing the agarose gel to cartilage by using the medical bio-adhesive, the full-thickness and half-thickness defects models of articular cartilage in vitro repaired by tissue engineering were constructed. Strain behaviors of the repaired region were analyzed by the digital correlation technology under 5, 10, 15, and 20% compressive load.ResultsThe axial normal strain (Ex) perpendicular to the surface of the cartilage and lateral normal strain (Ey) as well as shear strain (Exy) appeared obviously heterogeneous in the repaired region. In the full-defect model, Ex showed depth-dependent strain profiles where maximum Ex occurs at the low middle zone while in the half-defect mode, Ex showed heterogeneous strain profiles where maximum Ex occurs at the near deep zone. Ey and Exy at the interface site of both models present significantly differed from the host cartilage site. Ey and Exy exhibited region-specific change at the host, interface, and artificial cartilage sites in the superficial, middle, and deep zones due to the artificial cartilage implantation.ConclusionBoth defect models of cartilage exhibited a heterogeneous strain field due to the engineered cartilage tissue implant. The abnormal strain field can cause the cells within the repaired area to enter complex mechanical states which will affect the restoration of cartilage defects.

Numerical Simulation of Tibia-Femoral Joint Contact Mechanical Character

The biomechanical environment of knee joint is instrumental for understanding human joint function, damage and degeneration. The objectives of this study are to reconstruct the tibia-femoral joint finite element model of human in vivo, to simulate the joint mechanical character, especially in menisci and cartilage, and to understand the mechanism of menisci and cartilage of knee joint damage from mechanical aspect. Using the magnetic resonance imaging device we obtained the MRI date of knee joint in the straight position in vivo and then constructed the model. This model covered tibia plateau, femur, tibia cartilage, femoral cartilage and meniscus, using this model we simulate the distribution of the stresses and deformation of knee joint cartilage and meniscus. The material properties of cartilage and meniscus were derived from literature. This finite element model can be used as a non-invasive method for characterizing and monitoring subject-specific knee loading patterns.

The Influence of Some Biomechanical Factors on Endochondral Ossification on Long Bone

It is believed that the formation of endochondral ossification and the construction of the initial bone architecture are affected by some biomechanical factors. In 1987, Carter et al. have proposed a new set of rules in which mechanical stresses are thought to influence endochondral ossification and bone remodeling in the developing skeleton. Carter and Wong later proposed a theoretical time-dependent model of endochondral ossification and simulated the sequence of the appearance of morphological structures. The objectives of this study are to simulate the process of the bone growth and discuss the influence of some biomechanical factors on endochondral ossification on long bone. The discussed factors include load cases, empirical constant k and different mechanical stimulus related to bone growth. We conducted three-dimensional FE analysis of the model used by Carter and Wong. The results simulated showed that the empirical constant k 0.5 is reasonable, the bone growth equation with the strain energy density as the mechanical stimulus is more reasonable.

The Nonlinear Viscoelasticity of the Human Knee Articular Cartilage

The human knee cartilage play an important role in the knee joint. Osteoarthritis (OA) are related to knee joint cartilage. So the accurate description of the cartilage constitutive is the most important work for the understanding the cartilage test phenomenon. The role of viscoelasticity of collagen fibers in bovine articular cartilage was examined in compression and tension using stress relaxation measurements in the axial direction (normal to the articular surface. The human knee joint cartilage also shows the same viscoelastic property in compression and tension test using stress relaxation measurement in the direction (normal to the articular surface). The tension and compression test show the non-linear viscoelastic property. A viscoelastic fibril-reinforced model including fluid flow was used for analysis of the experimental data. The collagen fibrillar matrix was assumed to be viscoelastic with a strain-dependent tensile modulus, and the nonfibrillar matrix was modeled as linearly elastic. For axial tension, collagen viscoelasticity was found to account for most of the stress relaxation, while the effects of fluid pressurization on the tensile stress were negligible. So we use the viscoelastic constitutive to define the cartilage for simulating the tension and compression test. This study illustrates the essential and mainly role of collagen viscoelasticity. Introduction Articular cartilage provides a low friction, wear resistant bearing surface in diarthrodial joints and distributes stresses to the underlying bone. The articular cartilage consists of three major structural constituents: collagen fibers, proteoglycan matrix, and interstitial water. Recent developments in mathematical modeling have improved our understanding of cartilage mechanics, such as the high ratio of transient over equilibrium loads, the load-sharing between the solid and fluid phases, and the dependence of the apparent stiffness of the cartilage on loading velocity [1]. Experimentally, for the axial tension and compression test, the cartilage presents the non-linear viscoelastic property. Based on the test, there may be two load bearing mechanisms accounting for the transient mechanical behavior, i.e.a fluid-dependent and fluid-independent [2]. However, the contribution of structural constituents to each mechanism have not been fully investigated theoretically. Articular cartilage is a stiff, viscoelastic, fibril-composite material. The importance of collagen fibers for the mechanical function and integrity of cartilage has been demonstrated experimentally. Stress relaxation has been observed in tension and compression testing of cartilage, where the viscoelasticity is attributed primarily to the collagen fibers [2]. Many theories to explain articular cartilage behavior under loading, expressed in computational models that consider the nonlinearly tension and compression of the cartilage. There are several model account for the collagen network. (Li et al., 2000, 2002; Li and Herzog, 2004; Wilson et al. 2004b). And these models all include the viscoelastic behavior [3]. In current attempt to study the mechanisms of cartilage in cartilage, the collagen fibrillar matrix was assumed to be viscoelastic, and the nonfibrillar matrix was considered to linear elastic. For the tensile test, the transient response was dominated by collagen viscoelasticity. The most common tests used to determine the mechanical quality of articular are those of tension, confined compression, unconfined compression, indentation [3]. But none of theory models can explain all of the tests phenomenon. We hypothesized that a constitutive model considering collagen fiber and non-fibrillar matrix, not considering the fluid-dependent mechanism effect. The collagen fiber and non-fibrillar matrix were 236 Advances in Engineering Research (AER), volume 105 3rd Annual International Conference on Mechanics and Mechanical Engineering (MME 2016) Copyright

A Three-Dimensional Finite Element Model Constructed Using Magnetic Resonance Images of a Knee

Abstract. In recent years, MRI studies have resulted in a better understanding of the movement and deformation of the meniscus in the terbinafine connection and provide, information on the morphology of the articular cartilage. In this paper, we will use of computer-aided technique and MRI to reconstruct the shape of the living knee, and divide the mesh and add the material properties to create the three-dimensional nonlinear knee joint finite element model information. Examining the relative sliding and friction in the knee joint, I used the dynamic dominant non-linear finite element technique to simulate the photomechanical properties of the tibial femoral joint under different loads. Apply a pressure, in the 0 degree direction to calculate the change of each structure, including: maximum pressure, average pressure, contact pressure, internal stress.

Finite element simulation of inhomogeneity and anisotropy of femur

The finite element method has been increasingly adopted to study the biomechanical behavior of biologic structures. Once the finite element mesh has been generated from CT data set, the assignment of bone tissuepsilas material properties to each element is a fundamental step in the generation of individualized or subject-specific finite element models. The aim of this work is to simulate the inhomogeneity and anisotropy of the femur using the finite element method. A program is developed to read a CT data set as well as the finite element mesh generated from it, and to assign to each element of the mesh the material properties derived from the bone tissue density at the element location. Moreover, the transversely isotropy of femur is simulated by taking into account the principal material orientation for each element.