School of Chemical & Biomedical Engineering, Nanyang Technological University, Singapore, Singapore.
Acta Biomater. 2012 Jan;8(1):244-52. doi: 10.1016/j.actbio.2011.08.018. Epub 2011 Aug 25.
In cartilage tissue engineering, hydrogel is widely used as the scaffold for hosting and culturing chondrocyte suspension during neo-tissue formation. In order to develop cultured chondrocytes into a functional cartilage equivalent, the hydrogel must provide an ideal microenvironment for the rapidly proliferating chondrocytes. At the same time, the essential functions of chondrocytes, such as the secretion of type II collagen and glycosaminoglycans, must be maintained. In these studies, we quantitatively characterize the mechanobiology underlying a newly discovered "edge flourish" phenomenon of cultured chondrocytes within a three-dimensional agarose hydrogel, which may ultimately nurture scaffold-free cartilaginous tissue regeneration. First, real-time microscopy was used to track the spatiotemporal distributions of chondrocytes at different focal planes. The chondrocytes were observed to exhibit abundant neo-tissue outgrowth and significant cartilaginous phenotype at the edge of the hydrogel compared to those inside the hydrogel bulk. Secondly, the hydrogel surface stresses induced by the encapsulated chondrocytes were characterized quantitatively in real time using the finite-element method. Finally, the real-time three-dimensional matrix deformations of agarose hydrogel under the influence of chondrocytes were measured using a multiple-particle tracking assay. Our results indicate that the mechanism of the "edge flourish" phenomenon is induced by the oriented outgrowth of chondrocytic isogenous groups located at the edge of hydrogel. These isogenous groups exhibit directed outgrowth towards the surface of the hydrogel and eventually generate substantial surface tension on the interface of hydrogel and medium. Ultimately, the encapsulated chondrocytes closest to the hydrogel/medium interface will spontaneously sprout out of the hydrogel and form a layer of rich proliferative and chondrocytic extracellular matrix secreting chondrocytes at the surface of the hydrogel.
在软骨组织工程中，水凝胶被广泛用作支架，用于在新组织形成过程中承载和培养软骨细胞悬液。为了将培养的软骨细胞发育成具有功能的软骨等效物，水凝胶必须为快速增殖的软骨细胞提供理想的微环境。同时，必须维持软骨细胞的基本功能，如 II 型胶原蛋白和糖胺聚糖的分泌。在这些研究中，我们定量表征了在三维琼脂糖水凝胶中培养的软骨细胞新发现的“边缘茂盛”现象的力学生物学基础，这可能最终培育出无支架的软骨组织再生。首先，实时显微镜用于跟踪不同焦平面处软骨细胞的时空分布。与水凝胶体内部相比，观察到软骨细胞在水凝胶边缘表现出丰富的新组织生长和显著的软骨表型。其次，使用有限元法实时定量表征包封的软骨细胞所引起的水凝胶表面应力。最后，使用多粒子跟踪测定法测量琼脂糖水凝胶在软骨细胞影响下的实时三维基质变形。我们的结果表明，“边缘茂盛”现象的机制是由位于水凝胶边缘的同源软骨细胞的定向生长引起的。这些同源群体朝向水凝胶表面定向生长，并最终在水凝胶和介质的界面上产生大量表面张力。最终，最接近水凝胶/介质界面的包封软骨细胞将自发地从水凝胶中长出，并在水凝胶表面形成一层富含增殖和分泌软骨细胞的细胞外基质。
