Date of Award

1-1-2013

Document Type

Open Access Dissertation

Department

Chemistry and Biochemistry

Sub-Department

Chemistry

First Advisor

Qian Wang

Second Advisor

James M Sodetz

Abstract

For tissue engineering and regenerative medicine, it is important to understand factors directing the stem cell fate, including self-renewal, proliferation, differentiation, and apoptosis. Bone marrow derived mesenchymal stem cells (BMSCs) have the potential to differentiate into osteoblasts, chondrocytes, adipocytes, and smooth muscle cells. Specifically, in the field of bone tissue engineering, BMSCs are commonly used for in vitro osteogenesis studies. However the mechanisms and signaling pathways that these cells recognize material surface and utilize to differentiate are still unclear. This dissertation focuses on investigating the effect of surface nanotopography and functionalization on the promotion of osteogenic differentiation of BMSCs. Surface topographies were created by Tobacco mosaic virus (TMV) for chapter 1-5, Turnip yellow mosaic virus (TYMV) for chapter 6, and calcium phosphate crystals (CaP) for chapter 7. These surfaces were previously documented to promote osteogenesis.

The first two chapters present the study of early endogenous bone morphogenetic protein 2 (BMP2) expression pattern which is believed to be responsible for accelerated osteogenesis, and possible pathways that TMV substrate can induce BMP2 upregulation. It was discovered that BMP2 had a peak expression level at 8 hours after osteoinduction on TMV substrate, similar to stress-induced osteogenesis. The underlying mechanisms may be overlapping. Chapter 3 involves the decoration of adhesive peptide on the exterior surface of TMV particles via a Click reaction to improve cell adhesion on TMV

substrate. The results indicate that the presence of cell adhesive sequence combined with nanotopography of TMV substrate can further enhance the expression of osteospecific genes. Chapter 4 demonstrates the study of different TMV nanostructures on osteogenesis of BMSCs. TMV subunits can be diassembled and reassembled without internal RNA strand. However, the reassembled TMV was not stable in culture conditions. Native rod-like TMV particles are also transformed to spherical particles upon heat denaturation. Chapter 5 attempts to create a reproducible and even monolayer of TMV for consistent cell culture experiment utilizing layer-by-layer deposition. Nanoparticles are switched from TMV to TYMV in chapter 6 to study the effect of genetically modified TYMV presenting cell adhesive peptides on its surface on osteogenesis of BMSCs. Although both TMV and TYMV coated substrates have previously been reported to accelerate osteogenic differentiation, the particle shapes are distinctively different. TMV is a rod while TYMV is a sphere. The results illustrates that genetic mutation of TYMV is effective in displaying multivalent ligands on plant viral particles and mutant TYMV enhances BMSC adhesion depending on the amount of virus coating. The last chapter studies the osteoinductivity of calcium phosphate (CaP)-based surface generated in situ by nucleation on polyelectrolyte multilayer films. The novel fabrication of CaP coating is demonstrated as an example to easily create a biomimetic surface with controllable roughness on bone implant materials.

Collectively, the research presented in this dissertation explores into the osteogenic potential of BMSCs on different 2D surface topographies and functionalities, unique properties of these biogenic nanoparticles and biomimetic surface, and attempts to employ them as model systemsin order to gain insights into the design of functional biomaterials for medicinal tissue engineering and regenerative medicine applications .

Rights

© 2013, Pongkwan Sitasuwan

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