Tissue‐Scale Biomechanical Testing of Brain Tissue for the Calibration of Nonlinear Material Models

Abstract

Brain tissue is one of the most complex and softest tissues in the human body. Due to its ultrasoft and biphasic nature, it is difficult to control the deformation state during biomechanical testing and to quantify the highly nonlinear, time‐dependent tissue response. In numerous experimental studies that have investigated the mechanical properties of brain tissue over the last decades, stiffness values have varied significantly. One reason for the observed discrepancies is the lack of standardized testing protocols and corresponding data analyses. The tissue properties have been tested on different length and time scales depending on the testing technique, and the corresponding data have been analyzed based on simplifying assumptions. In this review, we highlight the advantage of using nonlinear continuum mechanics based modeling and finite element simulations to carefully design experimental setups and protocols as well as to comprehensively analyze the corresponding experimental data. We review testing techniques and protocols that have been used to calibrate material model parameters and discuss artifacts that might falsify the measured properties. The aim of this work is to provide standardized procedures to reliably quantify the mechanical properties of brain tissue and to more accurately calibrate appropriate constitutive models for computational simulations of brain development, injury and disease. Computational models can not only be used to predictively understand brain tissue behavior, but can also serve as valuable tools to assist diagnosis and treatment of diseases or to plan neurosurgical procedures. © 2022 The Authors. Current Protocols published by Wiley Periodicals LLC. This article was corrected on 16 April 2022. See the end of the full text for details.

Poro-viscoelastic material parameter identification of brain tissue-mimicking hydrogels

“…Until processing for mechanical testing, the samples were stored as a whole in phosphate-buffered saline (PBS) and maintained within a temperature range of 5 °C-10 °C. All samples were processed within a maximum of 6 h post-mortem time (Fountoulakis et al, 2001;Garo et al, 2007;Faber et al, 2022). The Frontiers in Bioengineering and Biotechnology frontiersin.org brain hemispheres were cut into coronal slices to expose the region around the corona radiata.…”

“…From an experimental perspective, characterizing the mechanical behavior of the human brain is an extremely delicate task, and experimental data reported in the literature are often contradictory ( Budday et al, 2017a ; Faber et al, 2022 ). There are also limited availability, costs and ethical aspects to be considered.…”

Modeling the finite viscoelasticity of human brain tissue based on microstructural information

“…Subsequently, the samples were subjected to three cycles of compression and tension (minimum and maximum stretches of $$\lambda = [H + \Delta z] / H = 0.85$$ and $$\lambda = 1.15$$, where H denotes the initial specimen height and $$\Delta z$$ the displacement in the direction of loading) and a compression relaxation test at $$\lambda = 0.85$$ with a holding period of 300 s. The experimental setup is described in more detail in ref. [11].…”

Insights into the Mechanical Characterization of Mouse Brain Tissue Using Microindentation Testing

“…It has been established that the brain is among the softest tissues in the human body and is characterized by a highly nonlinear, poroviscoelastic, and spatially heterogeneous mechanical response (Budday et al., 2020). Therefore, brain tissue testing is subject to many challenges that include access to samples, size of samples, complexity of the microstructure, reproducing physiological loading conditions, testing environment, and effectively establishing a better understanding of the relationship between microstructure and mechanical response (Faber et al., 2022). Additionally, despite extensive research efforts, the mechanical properties of brain tissue remain subject for debate with a wide range of values reported in literature (Budday et al., 2020).…”