In vitro models are invaluable tools for deconstructing the biological complexity of the periodontal ligament (PDL). Model systems that closely reproduce the 3-dimensional (3D) configuration of cell–cell and cell–matrix interactions in native tissue can deliver physiologically relevant insights. However, 3D models of the PDL that incorporate mechanical loading are currently lacking. Hence, we developed a model where periodontal tissue constructs (PTCs) are made by casting PDL cells in a collagen gel suspended between a pair of slender, silicone posts for magnetic tensile loading. Specifically, one of the posts was rigid and the other was flexible with a magnet embedded in its tip so that PTCs could be subjected to tensile loading with an external magnet. Additionally, the deflection of the flexible post could be used to measure the contractile force of PDL cells in the PTCs. Prior to tensile loading, second harmonics generation analysis of collagen fibers in PTCs revealed that incorporation of PDL cells resulted in collagen remodeling. Biomechanical testing of PTCs by tensile loading revealed an elastic response at 4 h, permanent deformation by 1 d, and creep elongation by 1 wk. Subsequently, contractile forces of PDL cells were substantially lower for PTCs under tensile loading. Immunofluorescence analysis revealed that tensile loading caused PDL cells to increase in number, express higher levels of F-actin and α–smooth muscle actin, and become aligned to the tensile axis. Second harmonics generation analysis indicated that collagen fibers in PTCs progressively remodeled over time with tensile loading. Gene expression analysis also confirmed tension-mediated upregulation of the F-actin/Rho pathway and osteogenic genes. Our model is novel in demonstrating the mechanobiological behavior that results in cell-mediated remodeling of the PDL tissue in a 3D context. Hence, it can be a valuable tool to develop therapeutics for periodontitis, periodontal regeneration, and orthodontics.

中文翻译：

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具有磁拉伸载荷的工程 3D 牙周韧带模型


体外模型是解构牙周韧带 （PDL） 生物学复杂性的宝贵工具。在天然组织中紧密再现细胞-细胞和细胞-基质相互作用的 3 维 （3D） 构型的模型系统可以提供生理相关的见解。然而，目前缺乏包含机械载荷的 PDL 的 3D 模型。因此，我们开发了一个模型，其中牙周组织结构 （PTC） 是通过将 PDL 细胞铸造在悬浮在一对细长硅胶柱之间的胶原凝胶中来制成的，用于磁拉伸加载。具体来说，其中一个柱子是刚性的，另一个是柔性的，其尖端嵌入了磁铁，因此 PTC 可以使用外部磁铁承受拉伸载荷。此外，柔性柱的偏转可用于测量 PTC 中 PDL 细胞的收缩力。在拉伸载荷之前，PTC 中胶原纤维的二次谐波生成分析表明，PDL 细胞的掺入导致胶原蛋白重塑。通过拉伸载荷对 PTC 进行的生物力学测试表明，PTC 在 4 h 时具有弹性响应，1 d 时永久变形，蠕变伸长率为 1 wk。随后，PTC 在拉伸载荷下的 PDL 电池的收缩力大大降低。免疫荧光分析显示，拉伸负荷导致 PDL 细胞数量增加，表达更高水平的 F-肌动蛋白和 α-平滑肌肌动蛋白，并与拉伸轴对齐。二次谐波生成分析表明，PTC 中的胶原纤维随着时间的推移随着拉伸载荷而逐渐重塑。基因表达分析还证实了张力介导的 F-肌动蛋白/Rho 通路和成骨基因的上调。 我们的模型在展示在 3D 环境中导致细胞介导的 PDL 组织重塑的机械生物学行为方面具有新颖性。因此，它可以成为开发牙周炎、牙周再生和正畸疗法的宝贵工具。