Polymer/Extracellular Matrix Composite Scaffolds for Articular Cartilage Regeneration
Mikos, Antonios G.
Doctor of Philosophy
Cartilage is highly dependent on its extracellular matrix (ECM) for many of its vital characteristics such as a low friction surface, high compressive strength, and force distribution. Unfortunately, articular cartilage is avascular in nature and exhibits limited capacity for self-healing. This thesis focused on fabricating polymer/ECM hybrid scaffolds containing bioactive signals able to direct chondrogenic differentiation for cartilage regeneration. To generate cartilaginous ECM within an electrospun fibrous poly(ε-caprolactone) (PCL) scaffold, co-cultures of chondrocytes, the primary cell type of cartilage, and mesenchymal stem cells (MSCs), a precursor of the chondrogenic lineage, were optimized for matrix production. Ultimately, co-cultures were used in an effort to improve ECM production within these scaffolds by utilizing cell-cell communication in order to reduce the number of chondrocytes needed due to their limited availability within the tissue and increased dedifferentiation upon expansion. It was found that glycosaminoglycan and collagen production in co-cultures with as few as 50% chondrocytes approximated ECM contents generated by cultures comprised entirely of chondrocytes. Additionally, the capability of these co-culture generated polymer/ECM hybrid scaffolds for directing the chondrogenesis of MSCs was examined. It was determined that MSCs grown on devitalized PCL/ECM scaffolds generated for 14 days by co-cultures of chondrocytes and MSCs in equal proportions led to similar chondrogenic gene expression patterns as on PCL/ECM scaffolds produced by chondrocytes alone with an increase in chondrogenic expression patterns compared to PCL controls. By investigating both direct and indirect co-culture methods, it was determined that cell secreted factors were sufficient for generating PCL/ECM hybrid constructs using chondrocytes and MSCs reducing the necessity of direct cell contacts between these cell types in both static and flow perfusion bioreactor cultures. Finally, nanoscale features were imparted within a microscale fibrous PCL scaffold utilizing dual extrusion electrospinning in order to examine the cellular benefits of scaffold architectures and compositions resembling native ECM. These studies led to a greater understanding of the interplay between chondrocytes and MSCs for the production of cartilaginous ECM and furthermore the influence of scaffold composition and architecture on the chondrogenic differentiation of MSCs.
Extracellular matrix; Cartilage; Co-cultures; Mesenchymal stem cells; Chondrocyte