Su Lijun, Wang Ming, Yin Jun, Ti Fei, Yang Jin, Ma Chiyuan, Liu Shaobao, Lu Tian Jian
State Key Laboratory of Mechanics and Control of Mechanical Structures, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, PR China; MIIT Key Laboratory for Multifunctional Lightweight Materials and Structures, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, PR China.
The Key Laboratory of Biomedical Information Engineering of Ministry of Education, School of Life Science and Technology, Xi'an Jiaotong University, Shaanxi 710049, PR China; Bioinspired Engineering & Biomechanics Center (BEBC), Xi'an Jiaotong University, Xi'an 710049, PR China.
Acta Biomater. 2023 Jan 1;155:423-435. doi: 10.1016/j.actbio.2022.11.009. Epub 2022 Nov 11.
Brain tissue is considered to be biphasic, with approximately 80% liquid and 20% solid matrix, thus exhibiting viscoelasticity due to rearrangement of the solid matrix and poroelasticity due to fluid migration within the solid matrix. However, how to distinguish poroelastic and viscoelastic effects in brain tissue remains challenging. In this study, we proposed a method of unconfined compression-isometric hold to measure the force versus time relaxation curves of porcine brain tissue samples with systematically varied sample lengths. Upon scaling the measured relaxation force and relaxation time with different length-dependent physical quantities, we successfully distinguished the poroelasticity and viscoelasticity of the brain tissue. We demonstrated that during isometric hold, viscoelastic relaxation dominated the mechanical behavior of brain tissue in the short-time regime, while poroelastic relaxation dominated in the long-time regime. Furthermore, compared with poroelastic relaxation, viscoelastic relaxation was found to play a more dominant role in the mechanical response of porcine brain tissue. We then evaluated the differences between poroelastic and viscoelastic effects for both porcine and human brain tissue. Because of the draining of pore fluid, the Young's moduli in poroelastic relaxation were lower than those in viscoelastic relaxation; brain tissue changed from incompressible during viscoelastic relaxation to compressible during poroelastic relaxation, resulting in reduced Poisson ratios. This study provides new insights into the physical mechanisms underlying the roles of viscoelasticity and poroelasticity in brain tissue. STATEMENT OF SIGNIFICANCE: Although the poroviscoelastic model had been proposed to characterize brain tissue mechanical behavior, it is difficult to distinguish the poroelastic and viscoelastic behaviors of brain tissue. The study distinguished viscoelasticity and poroelasticity of brain tissue with time scales and then evaluated the differences between poroelastic and viscoelastic effects for both porcine and human brain tissue, which helps to accurate selection of constitutive models suitable for application in certain situations (e.g., pore-dominant and viscoelastic-dominant deformation).
脑组织被认为是双相的，约80%为液体，20%为固体基质，因此由于固体基质的重排而表现出粘弹性，并由于流体在固体基质内的迁移而表现出多孔弹性。然而，如何区分脑组织中的多孔弹性和粘弹性效应仍然具有挑战性。在本研究中，我们提出了一种无侧限压缩-等长保持方法，以测量不同样本长度系统变化的猪脑组织样本的力随时间的松弛曲线。在用不同的长度相关物理量对测量的松弛力和松弛时间进行缩放后，我们成功地区分了脑组织的多孔弹性和粘弹性。我们证明，在等长保持期间，粘弹性松弛在短时间范围内主导脑组织的力学行为，而多孔弹性松弛在长时间范围内主导。此外，与多孔弹性松弛相比，发现粘弹性松弛在猪脑组织的力学响应中起更主导的作用。然后，我们评估了猪和人类脑组织的多孔弹性和粘弹性效应之间的差异。由于孔隙流体的排出，多孔弹性松弛中的杨氏模量低于粘弹性松弛中的杨氏模量；脑组织在粘弹性松弛期间从不可压缩变为多孔弹性松弛期间可压缩，导致泊松比降低。本研究为粘弹性和多孔弹性在脑组织中作用的物理机制提供了新的见解。意义声明：尽管已经提出了多孔粘弹性模型来表征脑组织的力学行为，但区分脑组织的多孔弹性和粘弹性行为仍然很困难。该研究通过时间尺度区分了脑组织的粘弹性和多孔弹性，然后评估了猪和人类脑组织的多孔弹性和粘弹性效应之间的差异，这有助于准确选择适用于某些情况（例如，孔隙主导和粘弹性主导变形）的本构模型。
