Small everyday objects, airplane parts, and even houses have one thing in common. They can all be made by 3D printing. In medicine too, we can use metal, ceramic and plastic materials to 3D print replicas of body parts, like the spine or this bone, and even personalized prosthesis. However, these degrade over time because, unlike our tissues, they are not made by living cells which can renew themselves and heal damages. In my research, I try to fix that by 3D printing human tissues. Not with ceramics or plastics, but with living cells. However this is challenging, because cells are fragile and would not survive a normal 3D printing process. So to make that possible, I design water-rich gels called bio-inks, that carry and nurture the cells during the printing step. In this way, this mixture of cells and gels can be sculpted into the desired architecture by using 3D printing nozzles, or even cell-friendly laser light. Drawing inspiration from how naturally cells build our organs, we understand how to provide the printed cells with all the necessary nutrients and signals to guide them towards maturation into functional organ parts. In this way, we take steps towards a future in which personalized medicine is possible and in which we can 3D print body parts to replace tissues damaged by trauma, tumors or aging.