In the field of computational biomechanics, investigators have primarily used commercial software that is neither geared toward biological applications nor sufficiently flexible to follow the latest developments in the field This lack of a tailored software environment has hampered research progress, as well as dissemination of models and results To address these issues, we developed the FEBio software suite (http://mrlsciutahedu/software/febio), a nonlinear implicit finite element (FE) framework, designed specifically for analysis in computational solid biomechanics This paper provides an overview of the theoretical basis of FEBio and its main features FEBio offers modeling scenarios, constitutive models, and boundary conditions, which are relevant to numerous applications in biomechanics The open-source FEBio software is written in C++, with particular attention to scalar and parallel performance on modern computer architectures Software verification is a large part of the development and maintenance of FEBio, and to demonstrate the general approach, the description and results of several problems from the FEBio Verification Suite are presented and compared to analytical solutions or results from other established and verified FE codes An additional simulation is described that illustrates the application of FEBio to a research problem in biomechanics Together with the pre- and postprocessing software PREVIEW and POSTVIEW, FEBio provides a tailored solution for research and development in computational biomechanics

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FEBio: finite elements for biomechanics.

Design of porous scaffolds for cartilage tissue engineering using a three-dimensional fiber-deposition technique.

Comparison of the equilibrium response of articular cartilage in unconfined compression, confined compression and indentation

Experimental verification of the role of interstitial fluid pressurization in cartilage lubrication.

Stresses in the local collagen network of articular cartilage: a poroviscoelastic fibril-reinforced finite element study

Nonlinear analysis of cartilage in unconfined ramp compression using a fibril reinforced poroelastic model.

A fibril reinforced nonhomogeneous poroelastic model for articular cartilage: inhomogeneous response in unconfined compression.

The stiffness of articular cartilage is a nonlinear function of the strain amplitude andstrain rate as well as the loading history, as a consequence of the ﬂow of interstitial waterand the stiffening of the collagen ﬁbril network. This paper presents a full investigation ofthe interplay between the ﬂuid kinetics and ﬁbril stiffening of unconﬁned cartilage disksby analyzing over 200 cases with diverse material properties. The lower and upper elasticlimits of the stress (under a given strain) are uniquely established by the instantaneousand equilibrium stiffness (obtained numerically for ﬁnite deformations and analyticallyfor small deformations). These limits could be used to determine safe loading protocols inorder that the stress in each solid constituent remains within its own elastic limit. For agiven compressive strain applied at a low rate, the loading is close to the lower limit andis mostly borne directly by the solid constituents (with little contribution from the ﬂuid). Incontrast, however in case of faster compression, the extra loading is predominantly trans-ported to the ﬁbrillar matrix via rising ﬂuid pressure with little increase of stress in thenonﬁbrillar matrix. The ﬁbrillar matrix absorbs the loading increment by self-stiffening:the quicker the loading the faster the ﬁbril stiffening until the upper elastic loading limitis reached. This self-protective mechanism prevents cartilage from damage since theﬁbrils are strong in tension. The present work demonstrates the ability of the ﬁbril rein-forced poroelastic models to describe the strain rate dependent behavior of articularcartilage in unconﬁned compression using a mechanism of ﬁbril stiffening mainly inducedby the ﬂuid ﬂow. @DOI: 10.1115/1.1560142#Keywords: Cartilage Mechanics, Fibril Reinforcement, Finite Element Analysis, Nonlin-ear Biomechanics, Poroelasticity

Strain-rate dependent stiffness of articular cartilage in unconfined compression

The role of viscoelasticity of collagen fibers in articular cartilage: axial tension versus compression.

Computational mechanics has been advanced in every area of orthopedic biomechanics. The objective of this paper is to provide a general review of the computational models used in the analysis of the mechanical function of the knee joint in different loading and pathological conditions. Major review articles published in related areas are summarized first. The constitutive models for soft tissues of the knee are briefly discussed to facilitate understanding the joint modeling. A detailed review of the tibiofemoral joint models is presented thereafter. The geometry reconstruction procedures as well as some critical issues in finite element modeling are also discussed. Computational modeling can be a reliable and effective method for the study of mechanical behavior of the knee joint, if the model is constructed correctly. Single-phase material models have been used to predict the instantaneous load response for the healthy knees and repaired joints, such as total and partial meniscectomies, ACL and PCL reconstructions, and joint replacements. Recently, poromechanical models accounting for fluid pressurization in soft tissues have been proposed to study the viscoelastic response of the healthy and impaired knee joints. While the constitutive modeling has been considerably advanced at the tissue level, many challenges still exist in applying a good material model to three-dimensional joint simulations. A complete model validation at the joint level seems impossible presently, because only simple data can be obtained experimentally. Therefore, model validation may be concentrated on the constitutive laws using multiple mechanical tests of the tissues. Extensive model verifications at the joint level are still crucial for the accuracy of the modeling.

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LePing Li

Papers

Nonlinear analysis of cartilage in unconfined ramp compression using a fibril reinforced poroelastic model.

A fibril reinforced nonhomogeneous poroelastic model for articular cartilage: inhomogeneous response in unconfined compression.

Strain-rate dependent stiffness of articular cartilage in unconfined compression

The role of viscoelasticity of collagen fibers in articular cartilage: axial tension versus compression.

Recent Advances in Computational Mechanics of the Human Knee Joint