Mesenchymal Stem Cell Fate on Carbon-Based Biomaterials: Implications for Bone Regeneration and Repair

Treatment of traumatic bone injuries is actively relying on tissue engineering strategies for bone repair. In this research, we examined mesenchymal stem cells (MSCs) on carbon-based biomaterials, with a long-term goal of bone regeneration. MSCs are adultderived cells that can differentiate into osteoblasts, and simultaneously stimulate osteoprogenitors in bone tissue environments. More specifically, carbon-based materials such as graphene, provides a bone-specific microenvironment for MSCs to undergo ossification. However, although the goal is new bone formation, signaling mechanisms to achieve bone differentiation can vary. Therefore, the over-arching focus of this research was to evaluate the osteogenic behavior of MSCs in the presence of graphene materials. This dissertation contains five chapters. In chapter 1, we reviewed 3D-printing graphene scaffolds for tissue engineering. However, developing graphene scaffolds first requires understanding of MSC activity on graphene surfaces. Therefore, chapter 2 examines MSCs cultured on a low-oxidized graphene substrate, which supported several genes important to bone differentiation. In chapter 3, we examined the gene expression profile of MSCs cultured on graphene oxide (GO) and reduced graphene oxide (rGO), the major graphene derivatives. We found that genetic activity of MSCs was robustly upregulated on rGO in comparison to GO substrates. Afterwards, we shifted to the in vivo ovariectomized (OVX) rodent model, which mimics post-menopause osteoporosis. In chapter 4, we found that MSCs derived from OVX rats lacked normal bone mineralization in comparison to MSCs derived from healthy rats. RNA sequencing analysis revealed that several genes important to bone differentiation were not upregulated in OVX-MSCs. We therefore postulated that osteoporotic-bone injuries could be restored by delivering healthy MSCs on a graphene scaffold. In chapter 5, we created a mandible defect in both sham and OVX animals, which was filled with a 3Dprinted rGO-MSC construct. After 60 days, we found similar bone regenerative potential between sham and OVX animals, suggesting that rGO-MSC scaffolds provides an optimal signaling environment within osteoporotic bone. iv Overall, this information is a foundation of the cell signaling network between MSCs and graphene materials. Future models could potentially use graphene materials to prime MSCs into the bone differentiation pathway prior to in vivo applications.