A plant or an animal cell uses numerous processes to sort and assemble tiny building blocks into larger molecules, to rebuild molecules or to dissolve them. Such processes depend on interactions between various cellular components and are pre-programmed at least in some of the building blocks. Using synthetic gel particles, scientists try to simulate these cellular procedures; however, mimicking the complexity of natural processes presents a formidable task for scientists. Researchers have now developed a set of four different, micrometer-sized building blocks, which can self-sort and co-assemble into defined compositions and disassemble at the push of a button.