Doctor of Philosophy, Sharif University of Technology (2018)
Master of Science, Ferdowsi University of Mashad (2012)
Bachelor of Science, Ferdowsi University of Mashad (2010)
David Camarillo, Postdoctoral Faculty Sponsor
Nonlinear mechanics of soft composites: hyperelastic characterization of white matter tissue components.
Biomechanics and modeling in mechanobiology
This paper presents a bi-directional closed-form analytical solution, in the framework of nonlinear soft composites mechanics, for top-down hyperelastic characterization of brain white matter tissue components, based on the directional homogenized responses of the tissue in the axial and transverse directions. The white matter is considered as a transversely isotropic neo-Hookean composite made of unidirectional distribution of axonal fibers within the extracellular matrix. First, two homogenization formulations are derived for the homogenized axial and transverse shear moduli of the tissue, based on definition of the strain energy density function. Next, the rule of mixtures and Hashin-Shtrikman theories are used to derive two coupled nonlinear equations which correlates the tissue shear moduli to these of its components. Closed-form solutions for shear moduli of the components are then obtained by solving these equations simultaneously. In order to validate the hyperelastic characteristics of components obtained in previous step, they are used in a bottom-up approach in a micromechanical model of the tissue with the aim of predicting the directional homogenized responses of the tissue. Comparison of model predictions with the experimental test results reported for corona radiata and corpus callosum white matter structures reveals very good agreements with the experimental results in both directions. The model predictions are also in good agreement with the analytical solution obtained by the iterated homogenization technique. Results indicate that axonal fibers are almost ten times stiffer than the extracellular matrix under large deformations.
View details for DOI 10.1007/s10237-019-01275-6
View details for PubMedID 31853724
A three-dimensional micromechanical model of brain white matter with histology-informed probabilistic distribution of axonal fibers
JOURNAL OF THE MECHANICAL BEHAVIOR OF BIOMEDICAL MATERIALS
2018; 88: 288–95
This paper presents a three-dimensional micromechanical model of brain white matter tissue as a transversely isotropic soft composite described by the generalized Ogden hyperelastic model. The embedded element technique, with corrected stiffness redundancy in large deformations, was used for the embedment of a histology-informed probabilistic distribution of the axonal fibers in the extracellular matrix. The model was linked to a multi-objective, multi-parametric optimization algorithm, using the response surface methodology, for characterization of material properties of the axonal fibers and extracellular matrix in an inverse finite element analysis. The optimum hyperelastic characteristics of the tissue constituents, obtained based on the axonal and transverse direction test results of the corona radiata tissue samples, indicated that the axonal fibers were almost thirteen times stiffer than the extracellular matrix under large deformations. Simulation of the same tissue under a different loading condition, as well as that of another white matter tissue, i.e., the corpus callosum, in the axonal and transverse directions, using the optimized hyperelastic characteristics revealed tissue responses very close to those of the experiments. The results of the model at the sub-tissue level indicated that the stress concentrations were considerably large around the small axons, which might contribute into the brain injury.
View details for DOI 10.1016/j.jmbbm.2018.08.042
View details for Web of Science ID 000448090700031
View details for PubMedID 30196184
Micromechanics of brain white matter tissue: A fiber-reinforced hyperelastic model using embedded element technique
JOURNAL OF THE MECHANICAL BEHAVIOR OF BIOMEDICAL MATERIALS
2018; 80: 194–202
A transverse-plane hyperelastic micromechanical model of brain white matter tissue was developed using the embedded element technique (EET). The model consisted of a histology-informed probabilistic distribution of axonal fibers embedded within an extracellular matrix, both described using the generalized Ogden hyperelastic material model. A correcting method, based on the strain energy density function, was formulated to resolve the stiffness redundancy problem of the EET in large deformation regime. The model was then used to predict the homogenized tissue behavior and the associated localized responses of the axonal fibers under quasi-static, transverse, large deformations. Results indicated that with a sufficiently large representative volume element (RVE) and fine mesh, the statistically randomized microstructure implemented in the RVE exhibits directional independency in transverse plane, and the model predictions for the overall and local tissue responses, characterized by the normalized strain energy density and Cauchy and von Mises stresses, are independent from the modeling parameters. Comparison of the responses of the probabilistic model with that of a simple uniform RVE revealed that only the first one is capable of representing the localized behavior of the tissue constituents. The validity test of the model predictions for the corona radiata against experimental data from the literature indicated a very close agreement. In comparison with the conventional direct meshing method, the model provided almost the same results after correcting the stiffness redundancy, however, with much less computational cost and facilitated geometrical modeling, meshing, and boundary conditions imposing. It was concluded that the EET can be used effectively for detailed probabilistic micromechanical modeling of the white matter in order to provide more accurate predictions for the axonal responses, which are of great importance when simulating the brain trauma or tumor growth.
View details for DOI 10.1016/j.jmbbm.2018.02.002
View details for Web of Science ID 000428486800025
View details for PubMedID 29428702
- Edge effects in adhesively bonded composite joints integrated with piezoelectric patches COMPOSITE STRUCTURES 2018; 200: 187–94
- A fresh insight into Kane's equations of motion ROBOTICA 2017; 35 (3): 498–510
- Relief of edge effects in bi-adhesive composite joints COMPOSITES PART B-ENGINEERING 2017; 108: 153–63
- On thermomechanical stress analysis of adhesively bonded composite joints in presence of an interfacial void COMPOSITE STRUCTURES 2015; 130: 116–23
- An analytical investigation on thermomechanical stress analysis of adhesively bonded joints undergoing heat conduction ARCHIVE OF APPLIED MECHANICS 2014; 84 (1): 67–79