Virus Particles Provide Nanotopographical Cues For Osteogenic Differentiation Of Mesenchymal Stem Cells

One key aspect of tissue engineering is to develop biomimetic scaffolding materials that can modulate the proliferation, self-renewal and differentiation of multipotent stem cells into different lineages. Bone marrow derived mesenchymal stem cells (BMSCs) can differentiate into several target cells such as osteoblasts, chondrocytes, adipocytes, and smooth muscle cells. BMSCs are commonly used for in vitro osteogenesis studies in bone tissue engineering field. However the mechanisms and signaling pathways that these cells use to recognize and response to biomaterial surface are still unclear. This dissertation focuses on investigating the effect of chemical and physical cues introduced by virus nanoparticles on the promotion of osteogenic differentiation of BMSCs by virus coated two dimensional substrates. Introduction to surface nanotopography influences on cell behaviors is highlighted in chapter 1. In this chapter, background and reports on the impact of different nanotopographies on stem cell behaviors are described. Then we investigated effects of particle shapes, nanoscale features, and surface chemistry on osteogenesis of BMSCs by utilizing substrates fabricated from five different plant viruses nanoparticles in chapter 2. Three shapes of virus nanoparticles (rod, fiber, and spherical) were used to investigate the effect of particle morphology. In each group of the same shape virus, different type of viruses were also included to examine whether surface nanoscale feature and different in amino acid sequence of coat protein can affect the differentiation. On the other hand, the ordered arrangement of coat proteins on virus nanoparticles has been well documented to exhibit astonishing effect on immune system stimulation. Likewise, we sought to examine this effect by comparing arrange and random organization of coat proteins on nanoparticles in chapter 3. For this study, the randomly coated TMV coat proteins on gold nanorods (TMV-GNRs) was assembled and used to represent nanoparticles with random TMV coat protein organization. Chapter 4 focuses on mechanical pathway of virus substrates mediated osteogenesis of BMSCs through a centralized modulator, bone morphogenetic protein 2 (BMP2) which is believed to be responsible for accelerated osteogenesis. The possible pathways associated with virus substrates induced BMP2 upregulation is further explored in this chapter. It was discovered that expression level of BMP2 and many genes involved in cell motility had significant alteration early after osteoinduction on TMV substrate. These results suggest stress-induced osteogenesis as the underlying mechanisms of virus substrates stimulated osteoblastic differentiation. Collectively, the research presented in this dissertation investigates the underlying mechanism of virus substrates mediate osteogenic differentiation of BMSCs in order to gain insights into the design of functional biomaterials for tissue engineering and regenerative medicine applications