Osteogenic and Chondrogenic Differentiation of rBMSCs on Microsphere-Based Scaffolds Sintered Using Subcritical CO2

Abstract

Large bone defects remain a major clinical orthopedic challenge. It has been predicted that osteoarthritis will affect over 100 million adults in the United States by the year 2030. Current treatments for repairing bone defects include the use of bone grafts (autologous and allogenic) or implants (polymeric or metallic). These approaches have significant limitations due to insufficient supply, potential disease transmission, rejection, cost and the inability to integrate with the surrounding host tissue. The engineering of bone and cartilage tissue offers new therapeutic strategies to treat bone defects. Several scaffold-based approaches have been used in the past. However, this thesis presents a novel microsphere-based scaffold approach, sintered using subcritical carbon dioxide for osteogenic and chondrogenic tissue regeneration. As a next step in the fabrication of three-dimensional tissue engineered scaffolds, this thesis primarily focused on subcritical carbon dioxide sintering for forming scaffolds, performance of these scaffolds in culture for 6 weeks, and evaluation of two different polymers in osteogenic and chondrogenic differentiation. In this investigation, both temperature and pressure (along with time) were necessary to control during the CO2 sintering of PCL (higher temperature and pressure conditions with longer exposure time), as opposed to PLGA, which was sintered at ambient temperature and pressure conditions (for 1 hour exposure). The results obtained showed the feasibility of using these constructs for bone and cartilage tissue regeneration. Biochemical analysis, gene expression and histological staining were used to analyze the data. The mechanical integrity of the constructs was evaluated at the beginning and end of the culture period. The onset of PLGA degradation for the CO2 sintered microspheres in this study appeared at 1.5 weeks which affected chondrogenesis. With osteogenesis, the Osteogenic PLGA group showed greater calcium content value over the Osteogenic PCL group while PCL retained its shape, size and mechanical integrity and had twice as many cells per construct at 6 weeks. In conclusion, this thesis lays a foundation to explore numerous applications using subcritical carbon dioxide sintering for tissue engineering applications.