Book excerpt: As liver disease becomes more prevalent, the development of an in vitro culture system to study disease progression and its repair mechanisms is essential. Typically, 2D cultures are used to investigate liver cell (e.g., hepatocyte) function in vitro; however, hepatocytes lose function rapidly when they were isolated from the liver. This has promoted researchers to develop 3D scaffolds to recreate the natural microenvironment of hepatic cells. For example, gelatin-based hydrogels have been increasingly used to promote cell fate processes in 3D. Most gelatin-based systems require the use of physical gelation or non-specific chemical crosslinking. Both of these methods yield gelatin hydrogels with highly interdependent material properties (e.g., bioactivity and matrix stiffness). The purpose of this thesis research was to prepare modularly crosslinked gelatin-based hydrogels for studying the influence of independent matrix properties on hepatic cell fate in 3D. The first objective was to establish tunable gelatin-based thiol-norbornene hydrogels and to demonstrate that the mechanical and biological properties of gelatin hydrogels can be independently adjusted. Furthermore, norbornene and heparin dual-functionalized gelatin (i.e., GelNB-Hep) was prepared and used to sequester and slowly release hepatocyte growth factor (HGF). The second objective was to investigate the viability and functions of hepatocytes encapsulated in gelatin-based hydrogels. Hepatocellular carcinoma cells, Huh7, were used as a model cell type to demonstrate the cytocompatibility of the system. The properties of GelNB hydrogels were modularly tuned to systematically evaluate the effects of matrix properties on cell viability and functions, including CYP3A4 activity and urea secretion. The last objective was to examine the effect of heparin immobilization on hepatocyte viability and functions. The conjugation of heparin onto GelNB led to suppressed Huh7 cell metabolic activity and improved hepatocellular functions. This hybrid hydrogel system should provide a promising 3D cell culture platform for studying cell fate processes.