On the characterization of the heterogeneous mechanical response of human brain tissue

Abstract

The mechanical characterization of brain tissue is a complex task that scientists have tried to accomplish for over 50 years. The results in the literature often differ by orders of magnitude because of the lack of a standard testing protocol. Different testing conditions (including humidity, temperature, strain rate), the methodology adopted, and the variety of the species analysed are all potential sources of discrepancies in the measurements. In this work, we present a rigorous experimental investigation on the mechanical properties of human brain, covering both grey and white matter. The influence of testing conditions is also shown and thoroughly discussed. The material characterization performed is finally adopted to provide inputs to a mathematical formulation suitable for numerical simulations of brain deformation during surgical procedures.

Regional variations in stiffness in live mouse brain tissue determined by depth-controlled indentation mapping

“…In quantitative terms, it is interesting to note that, converting the averaged values of E obtained in our measurements ( Fig. 2a) to shear moduli G by dividing E by 2(1+ν) (where ν = 0.5 is the Poisson's ratio of compressibility), one obtains values for G of 0.5-0.8±0.1 kPa, which is in good agreement with macroscopic (i.e., not localized) frequency sweep measurements reported in the literature [28,31,[50][51][52][53][54][55][56]. A direct comparison with other local measurements is unfortunately not possible, because the latter have been either performed on different kind of samples (different age, species, slicing direction) or under very diverse indentation stroke protocols, which, because of the highly viscoelastic behavior of the material, give rise to very different results [23-26, 29, 33-36, 57].…”

“…Previous studies on brain mechanics have been mainly limited to the comparison between white and gray matter, with results that are either inconsistent or lack quantitative structure analysis [23][24][25][26][27][28][29][30][31]. Only recently, one study has shown that the mechanical properties correlate with myelin content in bovine brain [24], while stiffness was found to scale with the cell nucleus area in spinal cord of mouse and retinal ruminant tissue [30,32].…”

Fifty Shades of Brain: A Review on the Mechanical Testing and Modeling of Brain Tissue

“…Figures 11 and 12 illustrate that brain tissue not only stiffens with increasing strain but also with increasing strain rate. Rate-dependence of brain stiffness has consistently been reported in the literature using different testing techniques: shear testing or oscillatory shear testing [44,127,151], uniaxial compression or tension [57,83,85,132,137,140], indentation [20,107,136,163], and magnetic resonance elastography [36,145]. Figure 11 illustrates uniaxial compression, tension, and simple shear experiments performed at strain rates of 0.33 and 0.0067 1/s, respectively.…”

The Strain Rates in the Brain, Brainstem, Dura, and Skull under Dynamic Loadings

“…It is known that the brain has a rate-dependent behavior and gets stiffer by increasing the loading rate [16,59]. That is why, in literature, it is common to conduct in vitro tests with certain strain rates to capture the wider properties of the brain [18,19,60]. Similar approaches have been applied to identify the material parameters of brainstem, dura, and other rate-dependent biological tissue [31,61].…”