Cell culture models using 2D substrates have provided important conceptual advances in understanding the biology of cells. However, cells grown on flat 2D surfaces can differ substantially from physiological environments. Animal models provide a useful tool to study biology in a physiologically relevant environment. However, animals models are expensive, time-consuming, use a significant amount of test material, and do not always provide a useful extrapolation to humans. In vitro 3D cell culture models bridge the gap between the two, allowing the study of human cells in a physiologically-relevant environment with the convenience and speed of an in vitro model.