Scaffold Free Microtissue Formation for Enhanced Cartilage Repair.

Given the low self-healing capacity of fibrocartilage and hyaline cartilage, tissue engineering holds great promise for the development of new regenerative therapies. However, dedifferentiation of cartilage cells during expansion leads to fibrous tissue instead of cartilage. The purpose of our study was to generate 3D microtissues, spheroids, mimicking the characteristics of native fibrocartilage or articular cartilage to use as modular units for implantation in meniscal and articular cartilage lesions, respectively, within the knee joint. A set of parameters was assessed to create spheroids with a geometry compatible with 3D bioprinting for the creation of a biomimetic cartilage construct. Fibrochondrocytes (FC) and articular chondrocytes (AC) spheroids were created using a high-throughput microwell system. Spheroid morphology,  viability, proliferation and extracellular matrix were extensively screened. After 2D expansion, FC and AC dedifferentiated, resulting in a loss of cartilage specific extracellular matrix proteins. Spheroid formation did not result in FC redifferentiation, but did lead to redifferentiation of AC, resulting in microtissues displaying collagen II, aggrecan and glycosaminoglycans. This study demonstrates 3D cartilage mimics that could have a potential application in the next generation of Autologous Chondrocyte Implantation procedures. Moreover, spheroids can be used as building blocks to create cartilage constructs by bioprinting in the future.