A shock-induced damage progression analysis on myelin sheath using molecular simulations

Myelin sheath are repetitive fat layers encapsulating and insulating neuronal cells. The primary role of the myelin sheath lies in facilitating uninterrupted signal transmission to the rest of the brain. As such, a clear understanding of how the myelin sheath responds to traumatic forces is crucial. While previous studies have primarily focused on myelin failure under incremental or quasi-static loading, these conditions allow sufficient time for the structure to reorganize and recover from the applied stress. In contrast, the response of the myelin sheath to sudden forces, such as those generated by blasts, remains poorly understood. Blast-induced shock waves are a specific type of traumatic force characterized by distinct overpressure and underpressure phases. In this study, molecular dynamics simulations are used to apply a shock impact to a myelin model and evaluate its behavior under extreme loading conditions. This manuscript focuses on two critical aspects: the modeling of the myelin sheath and the effects of shock waves under both subsonic and supersonic regimes relative to the sub-cellular level of brain tissue. Following an impact event, variations in density, axial pressure, and radial distribution functions, as well as mean-squared displacement, provide quantitative and qualitative measures for evaluating the system's response. Further insight into the rupture mechanism is gained through mean-squared displacement (MSD) analysis. Additionally, it is observed that the decay of peak pressure is more pronounced at supersonic speed, with a maximum drop of approximately 70 % around the lipid bilayer, compared to a 62.5 % drop at subsonic speed. This dynamic loading scenario simulates a realistic injury environment for the myelin structure, and aids in gaining a deeper understanding of the cellular-level response within brain tissue.