Microstructural Model of the Collagen Fibril using Finite Element Method

Microstructural Model of the Collagen Fibril using Finite Element Method

Sanchez, P.F.

Weinans, H.H. (mentor)
Zadpoor, A.A. (mentor)

Mechanical, Maritime and Materials Engineering

BioMechanical Engineering

BME

2013-11-29

The tendon is the connective tissues that attach the muscles to bones. It plays an important role in the mechanics of the articulation because the tendon transmits the tensile force from the muscle to the correspondent bone. Even though the tendons are designed to support different loading conditions, it generally accepted that mechanical loading plays the principal role in the development of tendinopathies. The mechanical properties of the tendon have been studied for many years; however, the mechanisms associated with the response at the microscopical scale are largely unknown. In the present work a computational structural model was developed to study the failure mechanics of the tendon fibril. The proposed model was implemented using finite element methodology (FEM). The mechanical properties of the components of the structure (collagen molecule, non-covalent bonds and crosslinks) are modeled based on the results obtained from molecular simulations available in the literature. In particular, the failure mechanisms of each element were implemented. The different components of the fibril were modeled separately and validated. The geometry of the fibril is based on the 2D Hodge-Petruska model. An automatic tool was developed to assembly the structure of the fibril, in that way different dimensions of the fibril could be modeled. To assess the accuracy and numerical stability of the simulations, a parametric study of the stabilization techniques used was performed. The results of this analysis show that the inclusion of the damage properties in the structure cause convergence difficulties and the values of the parameters of the numerical stabilization vary between models. Regardless, it was possible to analyze the mechanical behavior of the fibril. Different models were created and tested under tensile loading conditions. First, an analysis of the effect of the dimension on the response of the fibril was performed. The results show that the stress-stain response of the different dimension of the fibril is similar until the accumulation of the damage of the non-covalent bonds causes a change of the stiffness in the fibril. Then, the response varies according to the geometry and the crosslinks density. Second, a tensile test on a fibril with higher dimension was simulated. The results show similar responses to the experimental results of (Svensson et al., 2013). It was found that at small strain regimes the mechanical behavior of the fibril is dictated by the response of the non-covalent interactions, while at higher strains regimes, the stiffness of the structure is determined by the crosslinks, and shows a more rigid response. Finally, the model shows that the accumulation of the plastic deformation of the molecules at high strains leads to a brittle failure of the fibril.

tendon
fibril
failure
finite element method

http://resolver.tudelft.nl/uuid:6db70afa-fc9b-461c-981d-80520b5a7433

2015-11-29

Student theses

master thesis

(c) 2013 Sanchez, P.F.