Methods, systems, and apparatus, including computer programs encoded on a storage medium, for integrating components into objects that are to be 3D printed. One of the methods includes obtaining a three-dimensional model of a first object; receiving an input identifying an additional component; generating a digital representation of the additional component; integrating the digital representation of the additional component with the three-dimensional model; and providing the three-dimensional model with the integrated digital representation to a 3D printer for fabrication.