Biomedical Engineering Department, Rensselaer Polytechnic Institute, Troy, New York 12180-3590, USA.
Tissue Eng Part A. 2013 May;19(9-10):1223-32. doi: 10.1089/ten.tea.2012.0321. Epub 2013 Jan 24.
Engineering strategies guided by developmental biology may enhance and accelerate in vitro tissue formation for tissue engineering and regenerative medicine applications. In this study, we looked toward embryonic tendon development as a model system to guide our soft tissue engineering approach. To direct cellular self-assembly, we utilized laser micromachined, differentially adherent growth channels lined with fibronectin. The micromachined growth channels directed human dermal fibroblast cells to form single cellular fibers, without the need for a provisional three-dimensional extracellular matrix or scaffold to establish a fiber structure. Therefore, the resulting tissue structure and mechanical characteristics were determined solely by the cells. Due to the self-assembly nature of this approach, the growing fibers exhibit some key aspects of embryonic tendon development, such as high cellularity, the rapid formation (within 24 h) of a highly organized and aligned cellular structure, and the expression of cadherin-11 (indicating direct cell-to-cell adhesions). To provide a dynamic mechanical environment, we have also developed and characterized a method to apply precise cyclic tensile strain to the cellular fibers as they develop. After an initial period of cellular fiber formation (24 h postseeding), cyclic strain was applied for 48 h, in 8-h intervals, with tensile strain increasing from 0.7% to 1.0%, and at a frequency of 0.5 Hz. Dynamic loading dramatically increased cellular fiber mechanical properties with a nearly twofold increase in both the linear region stiffness and maximum load at failure, thereby demonstrating a mechanism for enhancing cellular fiber formation and mechanical properties. Tissue engineering strategies, designed to capture key aspects of embryonic development, may provide unique insight into accelerated maturation of engineered replacement tissue, and offer significant advances for regenerative medicine applications in tendon, ligament, and other fibrous soft tissues.
工程学策略在发育生物学的指导下，可能会增强和加速组织工程和再生医学应用中的体外组织形成。在这项研究中，我们将胚胎肌腱发育作为模型系统，指导我们的软组织工程方法。为了指导细胞的自我组装，我们利用激光微加工技术，在纤维连接蛋白衬里的不同附着生长通道。微加工生长通道引导人真皮成纤维细胞形成单一的细胞纤维，而无需临时的三维细胞外基质或支架来建立纤维结构。因此，所得到的组织结构和机械特性仅由细胞决定。由于这种方法的自组装性质，生长的纤维表现出胚胎肌腱发育的一些关键方面，例如高细胞密度、快速形成（在 24 小时内）高度组织化和对齐的细胞结构，以及钙粘蛋白-11 的表达（表明直接的细胞间粘附）。为了提供动态机械环境，我们还开发并表征了一种方法，在细胞纤维生长时对其施加精确的循环拉伸应变。在细胞纤维形成的初始阶段（接种后 24 小时）之后，以 8 小时的间隔施加 48 小时的循环应变，拉伸应变从 0.7%增加到 1.0%，频率为 0.5Hz。动态加载显著提高了细胞纤维的机械性能，线性区域刚度和破坏时的最大载荷几乎增加了一倍，从而证明了一种增强细胞纤维形成和机械性能的机制。旨在捕获胚胎发育关键方面的组织工程策略，可能为工程化替代组织的加速成熟提供独特的见解，并为肌腱、韧带和其他纤维状软组织的再生医学应用提供重大进展。
