DYNAMIC COMPRESSION PROMOTES CARTILAGE-LIKE FUNCTIONAL PROPERTIES IN MSC-SEEDED HYALURONIC ACID HYDROGELS

摘要

The specialized function of articular cartilage in distributing stresses during normal joint movement must be recapitulated in a successful engineered cartilage repair. Chondrocytes can generate in vitro cartilage constructs with mechanical properties at or near native levels [1-3] when cultured in specialized media formulations. While these advances in chondrocyte-based tissue engineering are highly instructive, the difficulty of obtaining sufficient numbers of healthy autologous chondrocytes represents a considerable challenge. To circumvent this limitation, many have evaluated mesenchymal stem cells (MSCs), an autologous cell type that can be expanded in vitro and with a demonstrated capacity for chondrogenic differentiation. Despite their potential, MSC-based engineered cartilage has yet to achieve functional properties comparable to those produced by chondrocytes in 3D culture [4-6]. In several recent studies, we have evaluated the potential of MSCs encapsulated within a photo-polymerizable hyaluronic acid (HA) hydrogel [7-8] to generate cartilage-like repair constructs. In early studies, construct mechanical properties were ～20 fold less than native cartilage [9]. Since that time, we have optimized the system to generate constructs with near-native functionality. These modifications included determination of an optimal HA macromer concentration (1% w/v) [10] and MSC seeding density (50-60 million MSCs/ml) [11]. In other studies, we and others have shown that dynamic loading can further improve the maturation of both chondrocyte- and MSC-based constructs [12-13]. For MSCs in agarose, anabolic response to daily dynamic compressive loading was dependent on a preliminary 3-week pre-culture period, during which time MSCs underwent chondrogenic differentiation and established a contiguous extracellular matrix [13]. HA, as a natural constituent of the cartilage microenvironment, provides a favorable biologic interface for MSC interaction through CD44 receptors, and can advance chondrogenesis relative to other photo-polymerizable materials (such as poly[ethylene glycol], PEG) that lack attachment sites [8]. The objective of the present study was thus to evaluate a number of different dynamic compressive loading regimens with the goal of improving functional properties of MSC-seeded HA constructs.