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Traumatic brain injury poses a major public health challenge with significant immediate and long-term effects. Repetitive head trauma is an ongoing area of research, and little is known about the response of cerebral blood vessels to such loading. This study investigated the mechanical response of cerebral arteries to repetitive overstretch, hypothesizing that repeated overstretch leads to cumulative damage. To test this hypothesis, middle cerebral artery segments from twelve piglets were subjected to sub-yield, high-rate overstretch of varying severities, with up to 10 repetitions. The stress-stretch behavior of the vessels revealed that repetitive overstretch caused progressive softening that increased with both overstretch magnitude and number of exposures. This softening was notably limited to the toe region, with no changes occurring in the higher-stress, linear portion of the repeated overstretch curves. Mild-to-moderate overstretches resulted in gradual softening, while severe overstretches caused dramatic softening with the first exposure and little further change with subsequent overstretches. Mildly damaged vessels displayed a small amount of recovery with time, but the magnitude of this recovery was minimal and declined with increasing repetitions and severity. No clear relationship was observed between collagen denaturation and the magnitude and number of overstretches. These findings provide important insights into the mechanics of cerebral vessels under repetitive loading, suggesting that vascular damage from repeated trauma accumulates, potentially exacerbating existing injury. These results increase understanding of soft tissue damage and inform the development of constitutive damage models for cerebral arteries, a critical tool needed to improve predictions of traumatic brain injury progression. STATEMENT OF SIGNIFICANCE: This study investigates the mechanical response of cerebral arteries to repetitive overstretch, revealing cumulative softening effects. Unlike previous studies focusing on single overstretch events, our research is the first to explore repetitive exposures in cerebral arteries and to report softening as a function of both overstretch magnitude and number of exposures. Given the role of cerebral vessels in maintaining a healthy brain and their contributions to the structural response of the brain in TBI events, progressive vessel softening in repetitive TBI may lead to increased vulnerability with the potential to exacerbate existing injury. These findings enhance understanding of soft tissue damage mechanisms, providing critical insights for developing constitutive damage models and improving injury predictions in repeated TBI. 

Abstract Traumatic brain injury (TBI), particularly from explosive blasts, is a major cause of casualties in modern military conflicts. Computational models are an important tool in understanding the underlying biomechanics of TBI but are highly dependent on the mechanical properties of soft tissue to produce accurate results. Reported material properties of brain tissue can vary by several orders of magnitude between studies, and no published set of material parameters exists for porcine brain tissue at strain rates relevant to blast. In this work, brain tissue from the brainstem, cerebellum, and cerebrum of freshly euthanized adolescent male Göttingen minipigs was tested in simple shear and unconfined compression at strain rates ranging from quasi-static (QS) to 300 s−1. Brain tissue showed significant strain rate stiffening in both shear and compression. Minimal differences were seen between different regions of the brain. Both hyperelastic and hyper-viscoelastic constitutive models were fit to experimental stress, considering data from either a single loading mode (unidirectional) or two loading modes together (bidirectional). The unidirectional hyper-viscoelastic models with an Ogden hyperelastic representation and a one-term Prony series best captured the response of brain tissue in all regions and rates. The bidirectional models were generally able to capture the response of the tissue in high-rate shear and all compression modes, but not the QS shear. Our constitutive models describe the first set of material parameters for porcine brain tissue relevant to loading modes and rates seen in blast injury.