Engineering of Gelatin Methacryloyl (GelMA) Hydrogels for Developing Biomimetic Tissue Constructs

Three-dimensional (3D) cell culture offers a more physiologically-relevant context for disease modeling and drug screening. Hydrogel-based biomaterials support the long-term culture of cells in 3D and enhance memetic cell-cell and cell-matrix interactions. Herein, gelatin methacryloyl (GelMA) hydrogel, a well-known photo-crosslinkable hydrogel, was selected for engineering of different tissue constructs. This Ph.D. thesis consists of four research components. First, the practicability of imprinting cell topography on GelMA hydrogel was investigated. A novel method was developed to fabricate cell-like niches over the hydrogel’s substrate, and its effects on cytocompatibility and drug susceptibility of breast cancer cells were studied. Cancer cells showed higher viability on imprinted GelMA while becoming more susceptible to the anticancer drug compared to the plain substrates. Second, GelMA hydrogel was tuned in terms of mechanical properties and porosity to facilitate in vitro myelination of dorsal root ganglia (DRG) neurons by Schwann cells (SCs). It was shown that the tuned GelMA enhanced single axonal generation (unlike collagen) and promoted DRGs’ interaction with SCs (unlike PDL). Staining with specific biomarkers, i.e., myelin basic protein and myelin-associated glycoprotein, showed the signs of myelination. Third, the role of temperature on bioprintability of GelMA bioinks in a two-step crosslinking strategy was investigated. Lowering the temperature can enhance the physical gelation of GelMA and consequently improve filament formation. Results showed that the decrease in the temperature could improve the printability and shape fidelity of the deposited hydrogel, particularly at 15 °C. Time-dependent mechanical testing confirmed higher elastic properties of the collected hydrogel at the lower temperature. Numerical results confirmed the effectiveness of hydrophobic nozzle in the printability of GelMA. It was concluded that the coil- i helix transition of the GelMA macromeres was responsible for the observed changes in hydrogel mechanical behavior and a drop in porosity and cytocompatibility. Fourth, a hydrogel-based 3D human intracranial aneurysm (IA) model was developed using liquid assisted injection molding. With clinically relevant dimensions and tuned fluidic and matrix properties, the essential endothelium was successfully lined inside the reconstructed IA over pre-cultured smooth muscle cells. Based on the characterized viscoelastic properties of the GelMA hydrogel and with the help of a fluid-structure interaction model, the capability of the IA construct model in predicting the response of the IA to different fluid flow profiles was demonstrated. Finally, using the techniques developed in this thesis, a new approach is suggested to fabricate a fully hydrogel-based platform for tissue engineering and organ-a-chip applications. The in vitro tissue models can be used to enable the growth of different cell types within the hydrogel and study complex in vivo microenvironments by providing built-in vasculature and interfaces while they also support drug testing and disease modeling.