SYNCHROTRON-BASED IMAGING AND TOMOGRAPHY OF HYDROGEL SCAFFOLDS FOR TISSUE ENGINEERING
Liu, Chenglin 1988-
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Tissue engineering aims to repair damaged tissues and organs by building artificial tissues using scaffolds. Recently, scaffolds made from hydrogels have shown great potential to encapsulate living cells to control the spatial distribution of the cells for various tissue engineering applications. Due to high water content, hydrogels are hard to visualize in aqueous environments, which is, however, essential to track the success of hydrogel scaffolds in their applications. Nowadays, synchrotron-based imaging holds huge promise for non-invasive high-resolution visualization of the cell-scaffold constructs in vitro and in vivo. The research presented in this thesis was aimed at preforming a preliminary study on the use of synchrotron-based imaging techniques in vitro to visualize scaffolds and cells in tissue engineering. Particularly, scaffolds were fabricated from alginate hydrogels and imaged in aqueous solution by means of various synchrotron imaging techniques. First, K-edge subtraction (KES) imaging with computed tomography (CT) visualized alginate scaffolds were taking advantage of barium contrast agents. In contrast to conventional physical methods, a novel chemical method to incorporate barium with alginate scaffolds was applied for the scaffold visualization. Second, chitosan micro-spheres (CMs) were encapsulated in alginate scaffolds as contrast agent for in-line phase contrast imaging (PCI). Chitosan can be visualized more easily by PCI than alginate so that the distribution of CMs can indicate the shape of the scaffolds. Lastly, a combination of absorption imaging and PCI were used to visualize both the encapsulated cells and alginate scaffolds. To visualize the cells, gold nano-particles (GNPs) were employed as a marker to generate absorption contrast. For the PCI of the scaffolds, samples of different alginate cross-linking levels were tested and examined for comparison. KES with barium contrast agents showed promising imaging results. The scaffolds which incorporated barium by a novel chemical method were imaged with brighter and highlighted edges than the physical method. Alginate/CMs scaffolds can be visualized by PCI and can also be clearly imaged if combining it with CT. It was found that increasing the concentration of CMs within scaffolds can improve the images, but can also inversely affect the fabrication of scaffolds. For cell/scaffold visualization, absorption radiography can produce some dark spots in the images, however those spots cannot be recognized as either GNPs marked cells or noise at the present study, suggesting that further research is needed. The visibility of the scaffold by PCI is found to mainly depend on the cross-linking time of alginate. Longer cross-linking time can help improve the contrast by PCI-CT for quantitative analysis of the structure. The present study shows that different synchrotron imaging schemes based on KES and PCI have potential to visualize hydrogel scaffolds in aqueous environments. The methods and findings of the present study would facilitate the development of non-invasive methods to visualize tissue scaffolds and cells in the future.
DegreeMaster of Science (M.Sc.)
CommitteeChen, Xiongbiao; Bugg, James D; Johnston, James D; Bergstrom, Donald J; Wahid, Khan A
Copyright DateOctober 2014