A structured substrate is described which is suitable for forming and hosting a crystal array, as well as associated methods for making and using such a structured substrate. The structured substrate is made by injection molding and has on one side a combination of macro- and micro-structured features. Each macro-structured feature comprises an edge that forms a perimeter around an enclosed area containing a large number of the micro-structured features. When a droplet of a solution containing molecules of interest and a solvent is deposited onto one of the enclosed areas such that it extends somewhat beyond the perimeter, the droplet slowly dries and shrinks through evaporation of the solvent, during which the edge acts to seed crystallization of the molecules, and the micro-structured features act to direct crystal growth from the seed into the enclosed area. The crystal thus forms over the whole of the enclosed area in a shape that conforms to the perimeter. Crystals of a desired size and shape can therefore be formed.