Date

2016

Author

Hastürk, Onur

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Mesenchymal stem cells (MSCs) are promising cell sources for tissue engineering applications as they can differentiate into a variety of adult cells types including osteoblasts. In vivo microenvironment of stem cells is known to provide both biochemical signals and micro- and nanoscale physical cues that influence the behavior and fate of stem cells. The use of soluble chemical factors is the most common strategy to guide the commitment of MSCs to specific lineages, but it is a cause of concern such as unsatisfactory results or potential side effects. Therefore, engineering of the substrate surfaces with the aim of mimicking in vivo physical cues is a promising approach to understand cell-substrate interactions and modulate the fate of MSCs. For this purpose, poly(methyl methacrylate) films were designed to have surfaces decorated with 4x4 µm² (P4G4), 8x8 µm² (P8G8) and 16x16 µm² (P16G16) square prism pillars of 8 µm height separated by 4, 8 and 16 µm gaps, respectively. One set of the substrates were treated with oxygen plasma to improve surface hydrophilicity. Human MSCs isolated from dental pulp tissues were cultured on these substrates and the influence of the dimension and hydrophilicity of micropatterns on attachment, conformational changes, proliferation and differentiation of cells were studied. The results showed that micropatterns increased cell attachment but decreased proliferation rate on the hydrophobic substrates; however, oxygen plasma modification promoted both attachment and proliferation rate on all substrates. Confocal micrographs and the following digital analysis of cell shapes revealed distinct deformations in varying degrees in the cytoskeleton induced by topographical features. These deformations were found to occur earlier and to a higher degree on plasma modified hydrophilic substrates. Cells cultured on substrates with smaller pillar and gap dimensions displayed significant deformations of their nuclei. The proliferation rates on these substrates were significantly lower compared to the control surfaces. The influence of micropatterns on the expression of stemness and osteogenesis related genes was determined by real time quantitative PCR method. Plasma modified substrates were found to downregulate the expression of stemness markers and did not lead to an increase in the expression of bone markers. Hydrophobic P4G4 and P8G8 surfaces having no oxygen plasma modification, however, caused a significant increase in the expression of the bone marker alkaline phosphatase (ALP) and demonstrated that unmodified hydrophobic micropillar structures induce osteogenesis without using any chemical osteogenic factors.  

Subject Keywords

Stem cells., Tissue engineering., Biomedical engineering., Mesenchymal stem cells.

URI

http://etd.lib.metu.edu.tr/upload/12620036/index.pdf
https://hdl.handle.net/11511/25699

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Graduate School of Natural and Applied Sciences, Thesis