Three-dimensional bioprinted culture platforms mimic the native microenvironment of tissues more accurately than two-dimensional cell cultures or animal models. Scaffold-free bioprinting eliminates many complications associated with traditional scaffold-dependent printing as well as provides better cell-to-cell interactions and long-term functionality. In this study, constructs were produced from bone marrow derived mesenchymal stem cells (BM-MSCs) using a scaffold-free bioprinter. These constructs were cultured in either osteogenic, chondrogenic, a 50:50 mixture of osteogenic and chondrogenic ('osteo-chondro'), or BM-MSC growth medium. Osteogenic and chondrogenic differentiation capacity was determined over an 8-week culture period using histological and immunohistochemical staining and RT-qPCR (Phase I). After 6 weeks in culture, individual osteogenic and chondrogenic differentiated constructs were adhered to create a bone-cartilage interaction model. Adhered differentiated constructs were cultured for an additional 8 weeks in either chondrogenic or osteo-chondro medium to evaluate sustainability of lineage specification and transdifferentiation potential (Phase II). Constructs cultured in their respective osteogenic and/or chondrogenic medium differentiated directly into bone (model of intramembranous ossification) or cartilage. Positive histological and immunohistochemical staining for bone or cartilage identification was shown after 4 and 8 weeks in culture. Expression of osteogenesis and chondrogenesis associated genes increased between weeks 2 and 6. Adhered individual osteogenic and chondrogenic differentiated constructs sustained their differentiated phenotype when cultured in chondrogenic medium. However, adhered individual chondrogenic differentiated constructs cultured in osteo-chondro medium were converted to bone (model of metaplastic transformation). These bioprinted models of bone-cartilage interaction, intramembranous ossification, and metaplastic transformation of cartilage into bone offer a useful and promising approach for bone and cartilage tissue engineering research. Specifically, these models can be potentially used as functional tissue systems for studying osteochondral defect repair, drug discovery and response, and many other potential applications.

中文翻译：

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无支架的生物打印成骨和成软骨系统，可模拟骨软骨生理。

三维生物打印的培养平台比二维细胞培养或动物模型更准确地模拟组织的天然微环境。无需支架的生物打印消除了与传统的依赖支架的打印相关的许多复杂问题，并提供了更好的细胞间相互作用和长期功能。在这项研究中，使用无支架的生物打印机从骨髓来源的间充质干细胞（BM-MSC）生产构建体。将这些构建物在成骨，成软骨，成骨和成软骨的50:50混合物（“成骨软骨”）或BM-MSC生长培养基中培养。使用组织学和免疫组织化学染色以及RT-qPCR（阶段I），在8周的培养期内确定了成骨和软骨形成的分化能力。经过6周的培养，粘附单个成骨和成软骨分化的构建体以创建骨-软骨相互作用模型。将粘附的分化构建体在软骨形成或骨软骨培养基中再培养8周，以评估谱系规格和转分化潜能的可持续性（第二阶段）。在其各自的成骨和/或软骨形成培养基中培养的构建体可直接分化为骨骼（膜内骨化模型）或软骨。培养4和8周后，显示出用于骨或软骨鉴定的阳性组织学和免疫组织化学染色阳性。成骨和软骨形成相关基因的表达在第2周到第6周之间增加。当在软骨形成培养基中培养时，粘附的单个成骨和软骨形成的分化构建体维持其分化表型。然而，在骨软骨培养基中培养的粘附的个体软骨形成分化构建体被转化为骨（化生转化模型）。这些关于骨-软骨相互作用，膜内骨化和软骨向骨的化生转化的生物打印模型为骨和软骨组织工程研究提供了有用且有希望的方法。具体来说，这些模型可以潜在地用作研究骨软骨缺损修复，药物发现和反应以及许多其他潜在应用的功能组织系统。在骨软骨培养基中培养的粘附的单个软骨生成分化构建体被转化为骨（化生转化模型）。这些关于骨-软骨相互作用，膜内骨化和软骨向骨的化生转化的生物打印模型为骨和软骨组织工程研究提供了有用且有希望的方法。具体来说，这些模型可以潜在地用作研究骨软骨缺损修复，药物发现和反应以及许多其他潜在应用的功能组织系统。在骨软骨培养基中培养的粘附的单个软骨生成分化构建体被转化为骨（化生转化模型）。这些关于骨-软骨相互作用，膜内骨化和软骨向骨的化生转化的生物打印模型为骨和软骨组织工程研究提供了有用且有希望的方法。具体来说，这些模型可以潜在地用作研究骨软骨缺损修复，药物发现和反应以及许多其他潜在应用的功能组织系统。软骨向骨骼的化生转化为骨骼和软骨组织工程研究提供了有用且有希望的方法。具体来说，这些模型可以潜在地用作研究骨软骨缺损修复，药物发现和反应以及许多其他潜在应用的功能组织系统。软骨向骨骼的化生转化为骨骼和软骨组织工程研究提供了有用且有希望的方法。具体来说，这些模型可以潜在地用作研究骨软骨缺损修复，药物发现和反应以及许多其他潜在应用的功能组织系统。