Transparent head surrogate for full-field in situ visualization of mechanical pathways of blast-induced brain injury

Understanding the mechanisms of blast-induced traumatic brain injury (bTBI) remains a major challenge due to the complex coupling of shock waves, skull deformations, and brain tissue responses. In this study, an anatomically accurate, transparent head surrogate incorporating realistic skull geometry, cerebrospinal fluid (CSF), and hydrogel brain tissue is developed to enable full-field in situ visualization of intracranial dynamics under controlled blast loading. Full-field displacement, strain, strain rate, and stress responses of the brain simulant under an incident overpressure of 100 kPa, 150 kPa and 200 kPa respectively are quantitatively studied using the three-dimensional digital image correlation (3D-DIC) method. The experimental results reveal rapid shock propagation through the brain, anisotropic deformation patterns and region-specific strain localization. The maximum principal strain increases from 0.075 under the incident overpressure of 100 kPa to 0.376 under 200 kPa, while the maximum strain rate changes from 19.13 s^-1 to 82.01 s^-1, exceeding the established thresholds for axonal injury. The brainstem and cerebellum exhibit the highest strain and strain-rate responses, highlighting their susceptibility to blast-induced injury. The maximum negative CSF pressure reaches -108.5 kPa, which is below the cavitation onset threshold, and no cavitation bubble is observed. These findings demonstrate that the transparent, high-biofidelity surrogate integrated with the 3D-DIC method provides a powerful platform for directly visualizing and quantifying the mechanical pathways of blast-induced brain injury, bridging the gap between experimental observations and computational modeling.