Scaffold‐ and serum‐free hypertrophic cartilage tissue engineering as an alternative approach for bone repair.

Human adipose stem/stromal cell (ASC) spheroids were used as a serum‐free in vitro model to recapitulate the molecular events and extracellular matrix organization that orchestrate a hypertrophic cartilage phenotype. Induced‐ASC spheroids (ø = 450 µm) showed high cell viability throughout the period of culture. The expression of collagen type X alpha 1 chain (COLXA1) and matrix metallopeptidase 13 (MMP‐13) was upregulated at week 2 in induced‐ASC spheroids compared with week 5 (P <.001) evaluated by quantitative real‐time PCR. In accordance, secreted levels of IL‐6 (P <.0001), IL‐8 (P <.0001), IL‐10 (P <.0001), bFGF (P <.001), VEGF (P <.0001), and RANTES (P <.0001) were the highest at week 2. Strong in situ staining for collagen type X and low staining for TSP‐1 was associated with the increase of hypertrophic genes expression at week 2 in induced‐ASC spheroids. Collagen type I, osteocalcin, biglycan, and tenascin C were detected at week 5 by in situ staining, in accordance with the highest expression of alkaline phosphatase (ALPL) gene and the presence of calcium deposits as evaluated by Alizarin Red O staining. Induced‐ASC spheroids showed a higher force required to compression at week 2 (P <.0001). The human ASC spheroids under serum‐free inducer medium and normoxic culture conditions were induced to a hypertrophic cartilage phenotype, opening a new perspective to recapitulate endochondral ossification in vivo. [ABSTRACT FROM AUTHOR]