Purpose: Even though various types of scaffolds have been used lately as a complement to microfracture, the exact mechanism of reported cartilage repair improvement when using scaffolds is still unclear. In this study, an effort has been made to identify the specific effects that scaffolds may have on the cells of reparation when using this technique. Methods: A 3-D model in vitro, representing microfracture and containing both chondrocytes and bone marrowderived cells in different experimental

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... conditions was made, and the cells were cultured for eight weeks. Subsequently, the constructs containing our 3-D model were removed from the cell culture medium, fixed in paraffin and analyzed with immunohistochemistry. Results: Bone marrow -derived cells migrated to the upper compartment of the construct through a perforated nylon membrane containing both enzymatically digested-and non-digested particulated cartilage. The histological sections were stained with hematoxylin, eosin, S-100, SOX-9, Gomori, and procollagen type I and II. When minced cartilage wasn't pretreated with collagenase, exclusively bone-derived cells have created new extracellular matrix as showed by the histological analysis. Conclusions: In this model of microfracture, bone-derived cells but not chondrocytes have shown to have an active role in new cartilage formation without predigestion with collagenase. Moreover, it seems that the addition of a chitosan-based scaffold may lead to the improvement of a new cartilage matrix synthesis and integration. This effect hasn't been seen without the use of scaffold or when a fibrin-or a collagen-based scaffold have been used.