MycoPrinter is an open source 3D bioprinter that prints mycelium substrate ready for inoculation with various types of fungi. MycoPrinter combines additive manufacturing with plant biological tissue to create living organisms sculpted into artistic shapes. As such, it brings together engineering, biological sciences, and art under the umbrella of open citizen science. The printer would allow printing relatively fine details that otherwise would be difficult to sculpt using regular mycelium growing techniques of mold-making. Any artist wanting to work with mycelium would be able to use the MycoPrinter. In this project, we start with a DIY 3D printer kit and modify its print head to extrude biological substrate. Starting with a 3D printer allows us to focus on the substrate and its extruder. A well-regarded ready-to-assemble 3D printer kit based on the open source RepRap project can be combined with a multi-substrate paste extruder, or better yet, an open source syringe pump design to create a basic 3D bioprinter.