Osteochondral (OC) defects are localized areas of injury or degeneration of articular cartilage and underlying
(subchondral) bone resulting in focal and degenerative lesions which if left untreated contribute to irreversible
and progressive joint deterioration leading to osteoarthritis (OA). OC defects are challenging to treat as the
damage occurs in both articular cartilage and subchondral bone, or more specifically at the OC interface,
involving tissues of distinct morphologic and molecular composition. Clinical treatments such as bone marrow
stimulation, debridement, autologous chondrocyte implantation, and OC autograft and allograft transplantation
may improve clinical symptoms, but do not treat the underlying pathology. Implantable tissue engineered
scaffolds that deliver mesenchymal stem cells (MSCs) hold great potential for cell-based OC defect repair as
they can be isolated from a variety of adult tissues, are readily expanded in culture, and have been shown to
undergo osteogenic and chondrogenic differentiation. Scaffolds embedded with gradients of diffusible growth
factors, adhesion ligands, and matrix stiffness have been shown to promote MSC differentiation into
chondrogenic and/or osteogenic lineage in 3D culture, however, most of these studies have been limited to
stimulating OC differentiation based on gradients of a single factor. We have previously developed novel
polymerization approaches that allow for the creation of synthetic hydrogel scaffolds with tunable and continuous
gradients of crosslink density and/or elastic modulus, proteolytically mediated degradation, and immobilized cell
adhesive peptides (RGD). Furthermore, we have shown that cells respond to these gradients through directed
and guided invasion and sprout formation in 3D culture. We hypothesize that spatiotemporal gradients of
proteolytic degradation, elastic modulus and integrin-binding peptide ligands can be used to regulate MSC
differentiation into osteogenic and chondrogenic lineage. This hypothesis will be addressed by the following
specific Aims: Aim 1. To define the effect of spatiotemporal gradients of proteolytic degradation, immobilized
RGD concentration, and matrix stiffness on MSC differentiation. Aim 2. To evaluate whether spatiotemporally
presented integrin-specific peptide ligands differentially promote MSC differentiation into osteogenic or
chondrogenic lineage. These studies will provide the first evidence of how spatiotemporal regulation of multiple
types of physiologically relevant gradients modulate MSC integrin expression and lineage commitment in 3D
culture in the absence of induction factors. These findings will contribute towards the development of implantable
tissue engineered scaffolds that can be used as MSC delivery vehicles to facilitate chondrogenic and osteogenic
differentiation for the regeneration of cartilage and bone.
