Finite element 3D modeling of mechanical behavior of mineralized collagen microfibrils

The aim of this work is to develop a 3D finite elements model to study the nanomechanical behaviour of mineralized collagen microfibrils, which consists of three phases, (i) collagen phase formed by five tropocollagen (TC) molecules linked together with cross links, (ii) a mineral phase (Hydroxyapatite) and (iii) impure mineral phase, and to investigate the important role of individual properties of every constituent. The mechanical and the geometrical properties (TC molecule diameter) of both tropocollagen and mineral were taken into consideration as well as cross-links, which was represented by spring elements with adjusted properties based on experimental data. In the present paper an equivalent homogenised model was developed to assess the whole microfibril mechanical properties (Young's modulus and Poisson's ratio) under varying mechanical properties of each phase. In this study both equivalent Young's modulus and Poisson's ratio which were expressed as functions of Young's modulus of each phase were obtained under tensile load with symmetric and periodic boundary conditions.Comment: Journal of Applied Biomaterials and Biomechanics 9, 3 (2011) xx

Study on the Impact of Diseases and Medical Treatments on Bone Mineral Density

Several diseases and medical treatments have been found to affect bone quality over decades. Bone mass characteristics summarized in bone mineral density (BMD), geometry, microarchitecture, and mechanical properties are the main parameters permitting to assess the quality of bone. Clinically, the diagnosis of bone diseases and the prediction of bone fracture are largely based on the BMD values. Thus, the investigation of how diseases and treatments alter the BMD value is primordial to anticipate additional treatment for the patient. In this chapter, we summarize the main research studies investigating diseases and treatments’ effects on bone quality and more specifically on BMD

Mechanobiological Behavior of a Pathological Bone

Bone density and bone microarchitecture are two principle parameters needed for the evaluation of mechanical bone performance and consequently the detection of bone diseases. The mechanobiological behavior of the skeletal tissue has been described through several mathematical models. Generally, these models fingerboard different length scale processes, such as the mechanical, the biological, and the chemical ones. By means of the mechanical stimulus and the biological factors involved in tissue regeneration, bone cells’ behavior and bone volume changes are determined. The emergence of bone diseases leads to disrupt the bone remodeling process and thus, induces bone mechanical properties’ alteration. In the present chapter, an overview of bone diseases and their relationship with bone density alteration will be presented. Besides, several studies treating bone diseases’ effect on bone remodeling will be discussed. Finally, the mechanobiological models proposed to treat bone healing and drugs’ effect on bone, are going to be reviewed. For this sake, the chapter is subdivided into three main sequences: (i) Bone remodeling, (ii) Bone deterioration causes, (iii) Mathematical models of a pathological bone, and (iv) Mechanobiological models treating bone healing and drugs effect

Multi-Criteria Decision Making for Medical Device Development

International audienceThe development of a new product is a complicated multi-stakeholder process with a significant risk of failure. This is particularly true in the medical device sector, where there are strict therapeutic, psychological, and normative constraints. This article presents a multi-criteria decision making process called “Define, Prioritize, Measure, and Aggregate” (DPMA). DPMA is designed to help engineering managers in decision making during the development process of new medical devices. The model is based on two sets of criteria linked to business and customer satisfaction. These criteria are weighted using the analytic hierarchy process (AHP) and group decision making (GDM) process. The performance of a medical device is measured according to each criterion. Furthermore, the final score of GO/NO GO alternatives are calculated with the simple additive weighting (SAW) method. A case study for the development of a new kind of femoral implant is presented to demonstrate the implementation of the DPMA process. This study shows that the application of the DPMA process during the design of a 3D printed femoral prosthesis provided engineering managers the key elements and green light to go ahead with the development of this medical device

New three-dimensional model based on finite element method of bone nanostructure: single TC molecule scale level

At the macroscopic scale, the bone mechanical behavior (fracture, elastic) depends mainly on itscomponents nature at the nanoscopic scale (collagen, mineral). Thus, an understanding of themechanical behavior of the elementary components is demanded to understand the phenomenathat can be observed at the macroscopic scale. In this article, a new numerical model based on finiteelement method is proposed in order to describe the mechanical behavior of a single Tropocollagenmolecule. Furthermore, a parametric study with different geometric properties covering themolecular composition and the rate hydration influence is presented. The proposed model has beentested under tensile loading. While focusing on the entropic response, the geometric parametervariation effect on the mechanical behavior of Tropocollagen molecule has been revealed using themodel. Using numerical and experimental testing, the obtained numerical simulation results seemto be acceptable, showing a good agreement with those found in literature

Effect of material and structural factors on fracture behaviour of mineralised collagen microfibril using finite element simulation

Bone is a multiscale heterogeneous material and its principal function is to support the body structure and to resist mechanical loads without fracturing. Numerical modelling of biocomposites at different length scales provides an improved understanding of the mechanical behaviour of structures such as bone, and also guides the development of multiscale mechanical models. Here, a three-dimensional nano-scale model of mineralised collagen microfibril based on the finite element method was employed to investigate the effect of material and structural factors on the mechanical equivalent of fracture properties. Fracture stress and damping capacity as functions of the number of cross-links were obtained under tensile loading conditions for different densities and Young's modulus of the mineral phase. The results show that the number of cross-links and the density of mineral as well as Young's modulus of mineral have an important influence on the strength of mineralised collagen microfibrils which in turn clarify the bone fracture on a macroscale. © 2014 © 2014 Taylor & Francis

Investigation of the Effect of Residual Stress Gradient on the Wear Behavior of PVD Thin Films

The control of residual stresses has been seldom investigated in multilayer coatings dedicated to improvement of wear behavior. Here, we report the preparation and characterization of superposed structures composed of Cr, CrN and CrAlN layers. Nano-multilayers CrN/CrAlN and Cr/CrN/CrAlN were deposited by Physical Vapor Deposition (PVD) onto Si (100) and AISI4140 steel substrates. The Cr, CrN and CrAlN monolayers were developed with an innovative approach in PVD coatings technologies corresponding to deposition with different residual stresses levels. Composition and wear tracks morphologies of the coatings were characterized by scanning electron microscopy, high-resolution transmission electron microscopy, atomic force microscopy, x-ray photoelectron spectroscopy, energy-dispersive x-ray spectroscopy, x-ray diffraction and 3D-surface analyzer. The mechanical properties (hardness, residual stresses and wear) were investigated by nanoindentation, interferometry and micro-tribometry (fretting-wear tests). Observations suggest that multilayer coatings are composed mostly of nanocrystalline. The residual stresses level in the films has practically affected all the physicochemical and mechanical properties as well as the wear behavior. Consequently, it is demonstrated that the coating containing moderate stresses has a better wear behavior compared to the coating developed with higher residual stresses. The friction contact between coated samples and alumina balls shows also a large variety of wear mechanisms. In particular, the abrasive wear of the coatings was a combination of plastic deformation, fine microcracking and microspallation. The application of these multilayers will be wood machining of green wood

Finite Element Analysis of the effect of High Tibial Osteotomy correction angle on articular cartilage loading

Osteoarthritis is a globally common disease that imposes a considerable ongoing health and economic burden on the socioeconomic system. As more and more biomechanical factors have been explored, malalignment of the lower limb has been found to influence the load distribution across the articular surface of the knee joint substantially. In this work, a three-dimensional finite element analysis was carried out to investigate the effect of varying the high tibial osteotomy correction angle on the stress distribution in both compartments of the human knee joint. Thereafter, determine the optimal correction angle to achieve a balanced loading between these two compartments. The developed finite element model was validated against experimental and numerical results. The findings of this work suggest that by changing the correction angle from 0 degrees to 10 degrees valgus, high tibial osteotomy shifted the mechanical load from the affected medial compartment to the lateral compartment with intact cartilage. The Von Mises and the shear stresses decreased in the medial compartment and increased in the lateral compartment. Moreover, a balanced stress distribution between the two compartments as well as the desired alignment were achieved under a valgus hypercorrection of 4.5 degrees that significantly unloads the medial compartment, loads the lateral compartment and arrests the progression of osteoarthritis. After comparing the achieved results against the ones of previous studies that explored the effects of the high tibial osteotomy correction angle on either clinical outcomes or biomechanical outcomes, one can conclude that the findings of this study agree well with the related clinical data and recommendations found in the literature