Attitude towards organ donation and the risks associated with organ transplantation drive the search for alternatives. One such alternative, albeit a conceptual level, could be the generation of an organ replacement in a controlled setting. For instance, growing suitable cells onto a printed matrix under appropriate conditions would then lead to the formation of a functional organ. How about the practical issues surrounding either duplication or de novo generation of an organ with, say, a device to print a suitable matrix and grow and differentiate cells on it? Here, we wish to outline selected safety-related questions arising from the ex vivo growth, differentiation and maintenance of cells or cell systems.