Chondrogenesis of Encapsulated MSCs

Patrick Erickson, Kevin B. Miles, Howard W.T. Matthew

Abstract

The human body lacks a mechanism to regenerate damaged articular cartilage. Shallow cartilage defects do not heal, and may progress until much of the cartilage in the joint has degraded. This study explored a modular tissue engineering approach that could be used to regenerate articular cartilage. Rat bone marrow mesenchymal stem cells (MSCs) were encapsulated in hollow, spherical microcapsules composed of an ionic complex of chitosan and either hyaluronan (HA) or a mixture of HA and chondroitin-4-sulfate (C4S). The encapsulated MSCs were cultured in chondrogenic medium for 3 weeks to induce differentiation. Cell morphology and organization were evaluated by phase contrast microscopy, while viability was assessed by Calcein/Ethidium staining. Histological staining was used to characterize the distribution of secreted proteoglycans and collagens type I, II, and X. Total collagen was determined using a hydroxyproline assay. Results to date show that the MSCs survived in all capsule types. In all of the capsules with hollow interiors, the MSCs distributed themselves into small clusters on the interior capsule surface. When cultured in chondrogenic medium, these cell clusters grew into larger, rounder structures, which were likely to be chondrocytes along with their secreted extracellular matrix (ECM). Hollow capsules made of HA had the most numerous cell clusters, and after 3 weeks in chondrogenic medium, the cells and ECM filled most of the capsule interior. Hollow capsules made of a mixture of HA and C4S appeared to have holes in their membranes, and the cell clusters in chondrogenic medium became large and round, but remained as discrete clusters, unlike in the HA capsules. Capsules made of HA with an interior filled with collagen type I shrank upon formation and condensed all of their cells together. The cells in chondrogenic medium seemed to form more continuous networks of cells and ECM in the capsule interior than did the same capsules cultured in growth medium. These results suggest that the cells differentiate in culture and produce ECM material, which shows the potential of the system to be used to regenerate cartilage.