Hybrid Matrix Design for Cartilage-Mediated Bone Tissue Engineering

Treatment of large and complex bone defects remains a significant clinical problem. Due to the defect size, the regeneration cannot rely on natural bone healing process for recovery. Traditional scaffold design supports bone formation through intramembranous ossification, which limits vascularization leading to graft core necrosis and poor bone formation. Functional long bones can be regenerated following a developmental engineering approach, which requires a transient hypertrophic-cartilage template that contains all necessary signals to initiate bone tissue formation, vascularization, remodeling, and establishment of a functional bone marrow. This dissertation will present the design of a hybrid matrix system consisting of a mechanically stable polymeric microsphere and a hyaluronan-fibrin hydrogel phase which will support the formation of hypertrophic-cartilage template. Thus, the specific aims of this thesis are (i) to design and fabricate Hyaluronan-Fibrin hydrogel phase that mimics the natural ECM and supports formation of hypertrophic-cartilage template, (ii) in vitro evaluation of polymer-hydrogel scaffold system’s potential for bone formation through endochondral ossification, and (iii) in vivo assessment of polymer-hydrogel scaffold system’s bone formation via endochondral ossification using a critical-calvarial mouse (NSG/Col3.6Tpz) model. With the in vitro and animal studies, we concluded with confidence that the engineered hybrid matrix supported the formation of a rich hypertrophic-cartilage template and its subsequent mineralization. For the first time, a hydrogel-polymer matrix system has been developed to support bone formation through a process similar to the way our long bones are developed; this matrix system can potentially serve as a superior candidate for segmental bone tissue engineering applications