Modelling indentation of human lower-limb soft tissue: simulation parameters and their effects
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O R I G I NA L A RT I C L E
Theodoros Marinopoulos · Lorenzo Zani · Simin Li · Vadim V. Silberschmidt
Modelling indentation of human lower-limb soft tissue: simulation parameters and their effects
Received: 18 March 2020 / Accepted: 1 October 2020 © The Author(s) 2020
Abstract Modern developments of biomedical applications demand a better understanding of mechanical behaviour of soft biological tissues. As human soft tissues demonstrate a significant structural and functional diversity, characterisation of their mechanical behaviour still remains a challenge. Limitations related with implementation of mechanical experiments on human participants lead to a use of finite-element models for analysis of mechanical responses of soft tissues to different loads. This study focuses on parameters of numerical simulation considered for modelling of indentation of a human lower limb. Assessment of the effect of boundary conditions on the model size shows that at a ratio of its length to the tissue’s thickness of 1.7 for the 3D model this effect vanishes. The numerical results obtained with models employing various sets of mechanical parameters of the first-order Ogden scheme were compared with original experimental data. Furthermore, high sensitivity of the resulting reaction forces to the indenting direction is demonstrated for cases of both linear and angular misalignments of the indenter. Finally, the effect of changes in material parameters and their domain on their contribution to the reaction forces is discussed with the aim to improve our understanding of mechanical behaviour of soft tissues based on numerical methods. The undertaken research with its results on minimal requirements for finite-element models of indentation of soft tissues can support inverse analysis of their mechanical properties and underpin orthopaedic and medical procedures. Keywords Finite-element analysis · Indentation · Hyperelastic · Soft tissue · Lower limb 1 Introduction Soft biological tissues are ensembles of cells of various types and their extracellular matrixes that together have a specific functionality. Biological tissues are among the most complex materials in terms of structural heterogeneity. This complicates the characterisation of their mechanical behaviour that depends strongly on the morphological features and mechanical behaviours of the underlying tissues and cell types. A human soft tissue consists of skin, adipose (fat), muscle, veins, each with its own substructure. The result of this complexity is an anisotropic mechanical response [1] varying throughout the tissue with the local morphology. Soft tissues are known to exhibit highly nonlinear [2] and time-dependent behaviours [3]. Due to high water concentration, soft tissues can be considered incompressible. Typically, soft tissues are characterised by their J-shaped stressstrain curves [3] with stress remaining (mostly) proportional to strain at initial small deformation, followed by a steep increase after reaching a certain deformation limit. Previous studies into me
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