3D biofabrication of cell-laden alginate hydrogel structures
Tabriz, Atabak Ghanizadeh
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Biofabrication has been receiving a great deal of attention in tissue engineering and regenerative medicine either by manual or automated processes. Different automated biofabrication techniques have been used to produce cell-laden alginate hydrogel structures, especially bioprinting approaches. , These approaches have been limited to 2D or simple 3D structures, however. In this thesis, a new extrusion-based bioprinting technique and a new simple, manual 3D biofabrication method are presented to culture cells in 3D. These methods do not rely on any complex fabrication methods. The bioprinting technique was developed to produce more complex alginate hydrogel structures. This was achieved by dividing the alginate hydrogel cross-linking process into 3 stages: primary calcium ion cross-linking for printability of the gel, secondary calcium cross-linking for rigidity of the alginate hydrogel immediately after printing and tertiary barium ion cross-linking for the long-term stability of the alginate hydrogel in the culture medium. Simple 3D structures including tubes were first printed to ensure the feasibility of the bioprinting technique. Complex 3D structures, such as branched vascular structures, were subsequently printed successfully. The static stiffness of the alginate hydrogel after printing was 20.18 ± 1.62 kPa which was rigid enough to sustain the integrity of the complex 3D alginate hydrogel structure during the printing. The addition of 60 mM barium chloride was found to significantly extend the stability of the cross-linked alginate hydrogel from 3 days to beyond 11 days without compromising the cellular viability. The results based on cell bioprinting suggested that the viability of U87-MG cells was 92.94 ± 0.91 % immediately after bioprinting. Cell viability was maintained above 88 ± 4.3 % in the alginate hydrogel over a period of 11 days. On the other hand, the manual biofabrication approach developed in this thesis enabled the fabrication of scalable 3D cell-laden hydrogel structures easily, without complex machinery. The technique could be carried out using only apparatus available in a typical cell biology laboratory. The fabrication method would involve micro coating cell-laden hydrogels covering the surface of a metal bar by dipping into cross-linking reagent CaCl2 or BaCl2, to form hollow tubular structures. This method could be used to form single- or multi-layered tubular structures. This fabrication method has incorporated the use alginate hydrogel as the primary biomaterial and secondary biomaterial could be added depending on the desired application. The feasibility of this method has been demonstrated by showing the cell survival rate and normal responsiveness of cells within these tubular structures using mouse dermal embryonic fibroblast cells and human embryonic kidney 293 cells containing a tetracycline responsive red fluorescence protein (tHEK cells). By adjusting the fabrication protocol, complex hollow alginate hydrogel structures could be generated.