Functionalization of the polysaccharide hydrogel gellan gum for tissue engineering applications
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Hydrogels have for long been a promising class of materials for tissue engineering applications. Essentially, hydrogels form a scaffold-like support structure for cells and provide an aqueous environment. This artificial environment mimics natural tissues and allows for the research on cells and the effect of factors onto cells. Furthermore, hydrogels can be used in regenerative medicine for cell delivery to damaged tissue. The herein studied hydrogel material is the polysaccharide gellan gum, which has been developed as a food additive, but has recently been proposed as a suitable tissue engineering material. Although most hydrogel materials are biocompatible and do not negatively affect cell growth, they are also biologically relatively inert. To combat this situation, various approaches have been described in the literature to functionalize hydrogels with an abundance of different bioactive molecules through the means of various chemical strategies. Likewise, gellan gum hydrogels have been used successfully in cell culture, but satisfying cell adhesion and response have not been achieved. This thesis work describes the chemical functionalization of gellan gum and the covalent binding of the protein avidin to the gellan gum. Avidin is a tetrameric protein which binds biotin with high specificity and affinity. This allows for the convenient and flexible modification of the gellan gum network with biotin-labelled compounds, notably biotinylated ligands for cell attachment and signaling. Therefore, sodium purified gellan gum was successfully functionalized with avidin over carbodiimide coupling. Self-supporting gel samples could be created from the functionalized gellan gum. Commercial gellan gum was purified with an established method and its elemental composition was analyzed with atomic absorption spectroscopy. The covalent coupling of avidin was verified with gel electrophoresis, while its functionality was determined with fluorescence spectroscopy. Hydrogel samples were formed with calcium and bioamines and the mechanical properties of the gels were examined with compression testing. The results verify that the presented approach offers a mild functionalization that does not disturb hydrogel gelation or the avidin-biotin binding. Further work is required to improve the cross-linking and gel sample production, in order to achieve consistent results of parallel samples with good gel structure and desired suitable mechanical behavior. The next steps will be to discern a suitable biotinylated bioactive cue, such as biotinylated RGD, and test the ability of the functionalized gellan gum to serve as a cell culture matrix.