New research shows that cell size and membranes may play a key role in regulating the distribution of molecules inside cells. This discovery offers a new unconventional method for manipulating artificial cells via their size and interfacial properties, or their boundaries, instead of through molecular modification of their chemical structure. This could aid multiple industries, from cosmetics to pharmaceuticals, which want to avoid unexpected changes to the properties of artificial cells in their products, such as when creating new medicines like vaccines.