Editorial: When Physics Meets Biology; Biomechanics and Biology of Traumatic Brain Injury

We have launched this special topic to focus on the critical relationships between physical forces, biomechanics, and biological responses in traumatic brain injury (TBI). Understanding the precise connection between physical force(s) and biological response(s), the " physical to biological coupling " is essential for developing high fidelity models in experimental TBI, for designing better protective devices and measures, for establishing more accurate diagnostics, and – most importantly – for identifying specific, evidence-based pharmacotherapies for TBI. Several of the contributions are dedicated to the very important topic of modeling various forms of brain trauma describing an in vitro model of cavitation (Cao et al.), models of mild TBI (Chen et al.). Blast-induced TBI poses special challenge for modeling and two reviews are dedicated to address some of the issues associated with blast-induced TBI research (Courtney and Courtney; Needham et al.). As US epidemiology data show, the importance of understanding penetrating TBI – sadly – has became even more urgent. Cernak et al. describe a novel model for penetrating TBI, whereas Davidsson and Risling provide a great example of using finite element modeling in penetrating TBI. This study, together with a review by Carlsen and Daphalapurkar, focusing on the importance of structural anisotropy in biofidelity of computational models, both include the possibility for more sophisticated material definitions and can implement increasingly more physiologically relevant measures of injury. The overview by Young et al. fills a critical gap by comparing the physics of high velocity penetrating, blunt impact and blast injuries. As these contributions illustrate, modeling TBI is a truly multidimensional problem. The first dimension, the physical forces are highly variable and complex. They vary from relatively low-speed, low kinetic energy, typical in traffic and sport accidents to high velocity, high kinetic energy type observed in explosive blast. The next dimension is how these forces interact with the head and ultimately with the brain, whether they interact with the entire head during acceleration– deceleration causing diffuse, closed head TBI, or if they are high velocity, concentrated kinetic energy propelling, e.g., a bullet penetrating the skull and brain parenchyma causing focal, open TBI, or the combination of various velocities and intensities. The next important, yet currently, understudied dimension in modeling is to take into account the directionality of the physical forces relative to the anatomy of the brain. The use of the new generation of sensors, such as the Vector mouth guard (or the …