Once damaged, articular cartilage has a limited potential to repair. Clinically, a repair tissue is formed, yet, it is often mechanically inferior fibrocartilage. The use of monolayer expanded versus naïve cells may explain one of the biggest discrepancies in mesenchymal stromal/stem cell (MSC) based cartilage regeneration. Namely, studies utilizing monolayer expanded MSCs, as indicated by numerous in vitro studies, report as a main limitation the induction of type X collagen and hypertrophy, a phenotype associated with endochondral bone formation. However, marrow stimulation and transfer studies report a mechanically inferior collagen I/II fibrocartilage as the main outcome. Therefore, this review will highlight the collagen species produced during the different therapeutic approaches. New developments in scaffold design and delivery of therapeutic molecules will be described. Potential future directions towards clinical translation will be discussed. New delivery mechanisms are being developed and they offer new hope in targeted therapeutic delivery.

中文翻译：

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关节纤维软骨-为什么透明软骨无法修复？

一旦受损，关节软骨的修复潜力有限。临床上会形成修复组织，但在机械上通常是纤维软骨不足。使用单层扩增的细胞与未使用的细胞可能解释了基于间充质基质/干细胞（MSC）的软骨再生中最大的差异之一。即，如许多体外研究所表明的，利用单层扩展的MSC的研究报告了主要的局限性，即诱导X型胶原蛋白和肥大，这是一种与软骨内骨形成有关的表型。然而，骨髓刺激和转移研究报告了机械不良的胶原蛋白I / II纤维软骨为主要结果。因此，本综述将重点介绍在不同治疗方法中产生的胶原蛋白种类。将描述支架设计和治疗分子的递送方面的新发展。将讨论未来可能的临床翻译方向。正在开发新的输送机制，它们为靶向治疗输送提供了新的希望。