Department of Industrial and Mechanical Engineering, University of Brescia, Via Branze 38 (BS), Italy.
Istituto Ospedaliero Fondazione Poliambulanza, Head and Neck Department, Neurosurgery, via Bissolati, 57(BS), Italy; "Technology for Health" PhD Program, University of Brescia, Via Branze 38 (BS), Italy.
J Mech Behav Biomed Mater. 2022 Jun;130:105204. doi: 10.1016/j.jmbbm.2022.105204. Epub 2022 Mar 28.
This study focuses on the variations in the brain tissue dynamic behaviour pointing out new insight into the material nonlinear viscoelasticity. Shear dynamic response curves are obtained in different working conditions in terms of strain sweep and superimposed static compression offsets (SCO) applied in orthogonal direction to the shear. The strain sweep mode is used to study the storage and loss moduli dependence on the amplitude of the applied strain. It is found that the material exhibits linear viscoelastic behaviour up to about 0.1% strain amplitude. Above this critical threshold, the storage modulus G' decreases rapidly with increasing dynamic strain amplitude and this effect is gradually intensified as the SCO are increased. In addition, it is observed that the loss factor (G''/G') increases by increasing the SCO applied to the specimens. The dynamic strain amplitude results of the storage modulus reveal that the elastic component of the brain tissue's stiffness (G') evaluated at low strain strongly increases with increasing static superimposed compression strain while the loss factor in the same strain range appears to be SCO independent. Finally, dynamic stiffness recovery after a large strain deformation is considered. The reduction in low amplitude dynamic modulus and subsequent recovery kinetics due to a perturbation is found to be independent of the level of the SCO. The same assessments were carried out on 5 consecutive strain sweep cycle loading. It has been noticed that at the last cycle, the dissipation peak is reduced, and the non-linearity of the curve begins earlier. This could be explained by the effects of cerebral edema on cells and their surrounding environment.
本研究关注脑组织动态行为的变化，为物质非线性黏弹性提供新的见解。在剪切方向正交施加应变扫掠和叠加静态压缩偏移（SCO）的不同工作条件下，获得剪切的动态响应曲线。应变扫掠模式用于研究存储和损耗模量与施加应变幅度的关系。结果表明，该材料在约 0.1%应变幅度下表现出线性黏弹性行为。在这个临界阈值以上，随着动态应变幅度的增加，存储模量 G'迅速下降，并且随着 SCO 的增加，这种效应逐渐增强。此外，观察到随着施加到样品上的 SCO 的增加，损耗因子（G”/G'）增加。存储模量的动态应变幅度结果表明，在低应变下评估的脑组织刚度的弹性分量（G'）随着静态叠加压缩应变的增加而强烈增加，而在相同应变范围内的损耗因子似乎与 SCO 无关。最后，考虑了大应变变形后的动态刚度恢复。由于扰动导致的低振幅动态模量的降低及其随后的恢复动力学被发现与 SCO 的水平无关。在 5 个连续应变扫掠循环加载中进行了相同的评估。注意到在最后一个循环中，耗散峰降低，曲线的非线性更早开始。这可以通过细胞及其周围环境的脑水肿的影响来解释。
