Rheological characterization of human brain tissue

Budday S, Sommer G, Haybaeck J, Steinmann P, Holzapfel GA, Kuhl E (2017)

Publication Language: English

Publication Type: Journal article, Original article

Publication year: 2017

Journal

DOI: 10.1016/j.actbio.2017.06.024

Abstract

The rheology of ultrasoft materials like the human brain is highly sensitive to regional and temporal variations and to the type of loading. While recent experiments have shaped our understanding of the time-independent, hyperelastic response of human brain tissue, its time-dependent behavior under various loading conditions remains insufficiently understood. Here we combine cyclic and relaxation testing under multiple loading conditions, shear, compression, and tension, to understand the rheology of four different regions of the human brain, the cortex, the basal ganglia, the corona radiata, and the corpus callosum. We establish a family of finite viscoelastic Ogden-type models and calibrate their parameters simultaneously for all loading conditions. We show that the model with only one viscoelastic mode and a constant viscosity captures the essential features of brain tissue: nonlinearity, pre-conditioning, hysteresis, and tension-compression asymmetry. With stiffnesses and time constants of $μ_{\infty} = 0.7$ kPa, $μ_{1} = 2.0$ kPa, and $τ_{1} = 9.7$ s in the gray matter cortex and $μ_{\infty} = 0.3$ kPa, $μ_{1} = 0.9$ kPa and $τ_{1} = 14.9$ s in the white matter corona radiata combined with negative parameters $α_{\infty}$ and $α_{1}$ , this five-parameter model naturally accounts for pre-conditioning and tissue softening. Increasing the number of viscoelastic modes improves the agreement between model and experiment, especially across the entire relaxation regime. Strikingly, two cycles of pre-conditioning decrease the gray matter stiffness by up to a factor three, while the white matter stiffness remains almost identical. These new insights allow us to better understand the rheology of different brain regions under mixed loading conditions. Our family of finite viscoelastic Ogden-type models for human brain tissue is simple to integrate into standard nonlinear finite element packages. Our simultaneous parameter identification of multiple loading modes can inform computational simulations under physiological conditions, especially at low to moderate strain rates. Understanding the rheology of the human brain will allow us to more accurately model the behavior of the brain during development and disease and predict outcomes of neurosurgical procedures.

Authors with CRIS profile

Silvia Budday Lehrstuhl für Technische Mechanik (LTM) Paul Steinmann Lehrstuhl für Technische Mechanik (LTM)

Related research project(s)

Modeling and computation of growth in soft biological matter Feb. 1, 2014 - June 30, 2020

Involved external institutions

Technische Universität Graz

Austria (AT) Stanford University

United States (USA) (US)

How to cite

APA:

Budday, S., Sommer, G., Haybaeck, J., Steinmann, P., Holzapfel, G.A., & Kuhl, E. (2017). Rheological characterization of human brain tissue. Acta Biomaterialia. https://doi.org/10.1016/j.actbio.2017.06.024

MLA:

Budday, Silvia, et al. "Rheological characterization of human brain tissue." Acta Biomaterialia (2017).

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