Heart valve disease is an increasing global burden affecting patients of all ages, ranging from pediatrics to the elderly. Unfortunately, there are currently no diagnostics for early detection or therapeutic treatment strategies. The only remedy for end-stage valve disease is a prosthetic heart valve replacement. However, these non-living prostheses do not possess the ability to remodel, integrate, and respond biologically with the patient, leading to life-long medications or multiple resizing surgeries. Tissue engineering offers an enticing strategy to fabricate living, biological heart valve conduits with growth and integration potential. While there has been advances in fabricating tissue engineered heart valves, there remains a challenge of producing a heterogenous valve. The focus of this dissertation was to develop and evaluate biomaterials and a bioreactor system that can better provide environments for cells to grow and remodel. A hybrid hydrogel biomaterial developed by incorporating solubilized decelluarlized aortic leaflets into a bioprintable base material promoted a myofibroblastic phenotype in encapsulated cells and led to more matrix deposition (Chapter 2). Next, a composite biomaterial was produced by conjugating nanocellulose crystalline with methacrylated gelatin. The material enhanced material properties and promoted a chondrogenic-like phenotype in encapsulated HADMSC (Chapter 3). Finally, a bioreactor system was built to capture a wide range of pressures and frequencies found in the pediatric and adult populations (Chapter 4). The system was validated by culturing ex vivo porcine heart valves and conditioning a bioprinted tissue engineered heart valve. Overall, the completion of this work advanced the field of tissue engineering heart valves by providing insights on two types of biomaterials that can modulate stem cell behavior and phenotype. The bioreactor system proved to be useful in future studies involving both engineered and ex vivo heart valves.