Center for Musculoskeletal Research, University of Rochester Medical Center, Rochester, NY, 14642, USA; Department of Biomedical Engineering, University of Rochester, Rochester, NY, USA.
Center for Musculoskeletal Research, University of Rochester Medical Center, Rochester, NY, 14642, USA; Department of Biomedical Engineering, University of Rochester, Rochester, NY, USA.
J Mech Behav Biomed Mater. 2022 Jun;130:105192. doi: 10.1016/j.jmbbm.2022.105192. Epub 2022 Mar 23.
Tendon injuries are very common and result in significant impairments in mobility and quality of life. During healing, tendons produce a scar at the injury site, characterized by abundant and disorganized extracellular matrix and by permanent deficits in mechanical integrity compared to healthy tendon. Although a significant amount of work has been done to understand the healing process of tendons and to develop potential therapeutics for tendon regeneration, there is still a significant gap in terms of assessing the direct effects of therapeutics on the functional and material quality specifically of the scar tissue, and thus, on the overall tendon healing process. In this study, we focused on characterizing the mechanical properties of only the scar tissue in flexor digitorum longus (FDL) tendons during the proliferative and early remodeling healing phases and comparing these properties with the mechanical properties of the composite healing tissue. Our method was sensitive enough to identify significant differences in structural and material properties between the scar and tendon-scar composite tissues. To account for possible inaccuracies due to the small aspect ratio of scar tissue, we also applied inverse finite element analysis (iFEA) to compute mechanical properties based on simulated tests with accurate specimen geometries and boundary conditions. We found that the scar tissue linear tangent moduli calculated from iFEA were not significantly different from those calculated experimentally at all healing timepoints, validating our experimental findings, and suggesting the assumptions in our experimental calculations were accurate. Taken together, this study first demonstrates that due to the presence of uninjured stubs, testing composite healing tendons without isolating the scar tissue overestimates the material properties of the scar itself. Second, our scar isolation method promises to enable more direct assessment of how different treatment regimens (e.g., cellular ablation, biomechanical and/or biochemical stimuli, tissue engineered scaffolds) affect scar tissue function and material quality in multiple different types of tendons.
肌腱损伤非常常见，会导致活动能力和生活质量显著下降。在愈合过程中，肌腱在损伤部位产生疤痕，其特征是细胞外基质丰富且无序，并与健康肌腱相比存在机械完整性的永久性缺陷。尽管已经做了大量工作来了解肌腱的愈合过程并开发潜在的肌腱再生治疗方法，但在评估治疗方法对疤痕组织（特别是）的功能和材料质量以及整体肌腱愈合过程的直接影响方面仍存在显著差距。在这项研究中，我们专注于在增殖和早期重塑愈合阶段仅表征屈肌腱（FDL）肌腱中疤痕组织的机械性能，并将这些特性与复合愈合组织的机械性能进行比较。我们的方法足够灵敏，可以识别疤痕和肌腱-疤痕复合组织之间在结构和材料特性上的显著差异。为了解决由于疤痕组织的小纵横比可能导致的不准确问题，我们还应用逆有限元分析（iFEA）根据具有准确样本几何形状和边界条件的模拟测试来计算机械性能。我们发现，从 iFEA 计算出的疤痕组织线性切线模量在所有愈合时间点均与从实验计算出的显著不同，从而验证了我们的实验结果，并表明我们实验计算中的假设是准确的。综上所述，这项研究首先表明，由于未受伤残端的存在，在不分离疤痕组织的情况下测试复合愈合肌腱会高估疤痕本身的材料特性。其次，我们的疤痕组织分离方法有望实现对不同治疗方案（例如细胞消融、生物力学和/或生化刺激、组织工程支架）如何影响多种不同类型肌腱中疤痕组织功能和材料质量的更直接评估。
