AO Research Institute Davos, Davos, Switzerland.
Institute for Biomechanics, ETH Zürich, Zürich, Switzerland.
J Mech Behav Biomed Mater. 2023 Jul;143:105900. doi: 10.1016/j.jmbbm.2023.105900. Epub 2023 May 11.
Intervertebral disc (IVD) degeneration and regenerative therapies are commonly studied in organ-culture experiments with uniaxial compressive loading. Recently, in our laboratory, we established a bioreactor system capable of applying loads in six degrees-of-freedom (DOF) to bovine IVDs, which replicates more closely the complex multi-axial loading of the IVD in vivo. However, the magnitudes of loading that are physiological (able to maintain cell viability) or mechanically degenerative are unknown for load cases combining several DOFs. This study aimed to establish physiological and degenerative levels of maximum principal strains and stresses in the bovine IVD tissue and to investigate how they are achieved under complex load cases related to common daily activities. The physiological and degenerative levels of maximum principal strains and stresses were determined via finite element (FE) analysis of bovine IVD subjected to experimentally established physiological and degenerative compressive loading protocols. Then, complex load cases, such as a combination of compression + flexion + torsion, were applied on the FE-model with increasing magnitudes of loading to discover when physiological and degenerative tissue strains and stresses were reached. When applying 0.1 MPa of compression and ±2-3° of flexion and ±1-2° of torsion the investigated mechanical parameters remained at physiological levels, but with ±6-8° of flexion in combination with ±2-4° of torsion, the stresses in the outer annulus fibrosus (OAF) exceeded degenerative levels. In the case of compression + flexion + torsion, the mechanical degeneration likely initiates at the OAF when loading magnitudes are high enough. The physiological and degenerative magnitudes can be used as guidelines for bioreactor experiments with bovine IVDs.
椎间盘（IVD）退变和再生疗法通常在具有单轴压缩载荷的器官培养实验中进行研究。最近，我们实验室建立了一种生物反应器系统，能够对牛 IVD 施加六自由度（DOF）的载荷，更接近 IVD 在体内的复杂多轴加载。然而，对于结合多个 DOF 的载荷情况，生理（能够维持细胞活力）或机械退变的载荷大小尚不清楚。本研究旨在确定牛 IVD 组织中最大主应变和主应力的生理和退变水平，并研究在与常见日常活动相关的复杂载荷情况下如何达到这些水平。通过对牛 IVD 进行有限元（FE）分析，确定了生理和退变状态下最大主应变和主应力的生理和退变水平，该分析基于实验确定的生理和退变压缩加载方案。然后，对 FE 模型施加复杂的载荷情况，例如压缩+弯曲+扭转的组合，随着载荷大小的增加，发现达到生理和退变组织应变和应力的情况。当施加 0.1 MPa 的压缩和±2-3°的弯曲和±1-2°的扭转时，所研究的机械参数保持在生理水平，但当与±2-4°的扭转结合时，弯曲达到±6-8°，外纤维环（OAF）的应力超过退变水平。在压缩+弯曲+扭转的情况下，当载荷足够大时，机械退变可能首先发生在 OAF。生理和退变的幅度可作为牛 IVD 生物反应器实验的指南。
