Material properties of human brain tissue suitable for modelling traumatic brain injury

Finite element (FE) brain models have revolutionised research on the biomechanics of traumatic brain injury (TBI). The accuracy and reliability of results arising from brain models depend equally on their geometric accuracy as the quality of the material properties used to describe the mechanical behaviour of brain. However, much of the literature on human brain tissues’ material properties have been performed at low strain rates and strains. This is particularly striking considering a large portion of the brain tissue mechanical characterisation literature is presented with a motivation of understanding brain tissues’ behaviour during TBI which occurs due to brain tissues’ exposure to large strains at high strain rates. Therefore, the aim of this review is to collate the mechanical characterisation studies on human brain tissue under conditions suitable for modelling TBI. We first review injury threshold studies and show that ≥20% strain at ≥10/s strain rate is a reasonable minimum threshold for producing injury to the brain. Using this threshold, we show that there are only five studies on the mechanical characterisation of human brain tissue under strains at strain rates relevant to TBI. These studies, provide material properties of human brain tissue at moderate and high rate loading, with only a recent study showing its region dependent characteristics. This review acts as a reference for scientists and engineers to select suitable material data when modelling human TBI. It also calls for more research to provide high fidelity material properties for modelling of TBI.

Statement of significance

The significance of this work is underscored by the reporting of brain tissues’ material properties in the context of traumatic brain injury (TBI) despite these properties having been characterised under strains and strain rates that are not relevant to TBI. This can result in inaccurate results if implemented in finite element brain models. Here, we address this problem by performing a review on the mechanical characterisation of human brain tissue under conditions that are suitable for modelling human TBI. Our findings show that there are only five studies on the mechanical characterisation of human brain tissue under strains at strain rate levels relevant to TBI. These results will allow researchers to select appropriate material properties for modelling human TBI providing more realistic behaviour of brain tissue in simulations. These results also provide minimum strain and strain rate values for mechanical characterisation experiments on brain tissue for TBI applications. Furthermore, our findings highlight the lack of suitable material properties of human brain tissue for modelling TBI and calls for more research into mechanical characterisation of human brain tissue under large strain at high strain rates.