The complexity of living systems poses a formidable challenge to physical scientists interested in biology. I will discuss one theoretical approach towards gaining possible insight into biological phenomena: to design systems to exhibit similar phenomena. To do so, we start with systems with complex energy/cost landscapes, which have far more variation in their properties than those with simple ones. This natural variation can be pushed even further by design, allowing us to tune in properties than those common in living matter, such as the ability of proteins (e.g. hemoglobin) to change their conformations upon binding of an atom (oxygen) or molecule, or the ability of the brain's vascular network to send enhanced blood flow and oxygen to specific areas of the brain associated with a given task. We create ensembles of systems designed for a given task to gain new insight into the relation between microscopic structure and function that may help us understand living systems.