MINERAL DISTRIBUTION SPATIALLY PATTERNS MESENCHYMAL STEM CELL BEHAVIOR ON MONOLITHIC BONE SCAFFOLDS
The interfaces between soft tissue and bone at the ends of ligaments, tendons, and menisci, known as entheses, are characterized by their continuous apatitic mineral gradients. These interfacial tissues are essential to joint health, since they connect different tissues and mediate substantial changes in mechanical properties across the entheses. When damage occurs under extreme joint loading within an enthesis, repair of the enthesis is required to support growth locomotion and stability of joints. Implants are one possible repair route and fabricating implants that recapitulate the mineral gradient in native entheses can be challenging due to the complex, hierarchical structure of the interfacial tissue between bone and soft tissue. Tissue engineering provides a potential solution to repair damaged enthesis tissue by developing scaffolds that can be remodeled to mimic the extracellular matrix (ECM). Previously, we have demonstrated a ‘top-down’ method to create a monolithic bone scaffold with patterned mineral distribution at a scale around 40 microns and well-preserved native structure of trabecular bone. In this thesis, the cellular response to these scaffolds was studied. Mesenchymal stem cells (MSCs), which are the progenitor of most cells populations found in entheses, were seeded onto the scaffolds. Immunohistochemical (IHC) and histological stains were used to characterize their cellular behavior in regions of different mineral content. We found that MSCs in mineralized regions of the scaffold showed upregulated expression of osteogenic biomarkers, alkaline phosphatase (ALP) and osteocalcin (OCN) regardless of the presence of osteogenic biochemical cues in media. In contrast, MSCs in the demineralized regions of the scaffold showed downregulation of osteogenesis. In a chondrogenic biochemical environment, although osteogenesis was suppressed, MSCs in the mineralized regions of the scaffolds still showed improved osteogenesis compared to those in the demineralized regions of the scaffolds. These results indicate that we can spatially control the osteogenesis of the MSCs using our bone scaffolds with spatially distributed mineral. Additionally, this study provides the framework to tissue engineer an entire enthesis with more biomimetic cellular complexity and better integration between soft and hard tissue.
biomineral; bone scaffold; chondrogenesis; enthesis engineering; osteogenesis; Materials Science; Stem cells; Bioengineering
Estroff, Lara A.
Materials Science and Engineering
M.S., Materials Science and Engineering
Master of Science
dissertation or thesis