This is an explanation of the first circuit we ever printed directly onto a 3D printed component. The design goal of the print was purely to make something interesting with a 3D printed object used as the substrate (this test was done using PLA). We decided upon an LED matrix because we're hoping to play around with some cool stuff embedding LEDs into clear plastic 3D prints in the future. The circuit diagram and an image demonstrating how I generated the tracks are shown below. Again, I designed these tracks in a CAD program called Vectorworks for no other reason than I work fastest in this medium (sorry, that means no Eagle file for modification just yet). This design uses 0805 LEDs and a single 1206 0R jumper to skip over one of the tracks. The 3D printed part was also designed in Vectorworks and has offsets in the surface so the LEDs can be placed upside down with the bulb poking through to the other side and the bottom remaining flush with the surface of the 3D print (the size of these holes are tuned to fit an LED on the Ultimaker printer I was using at the time so may not fit perfectly on your own machine without some tweaking). To assemble the circuit, conductive epoxy must be used to avoid melting the plastic (but a light heat source can help in speeding up the drying process of the epoxy). It should also be noted that I used a small amount of PVA glue to fill some small surface gaps in the 3D print before putting it into the Argentum. This is simply because FDM printing isn't perfect and is forced to leave tiny gaps in some layers. If your slicer is very good or you use an alternate form of 3D printing (3DP, SLS, SLA) this wouldn't be needed. I've attached a 600DPI version of the image, perfect for printing with the Argentum control software as well as an stl of the 3D printed part, oriented the way I printed mine.