University of Pennsylvania engineers modified the RepRap open source 3D printer to spew out vascular networks made from sugar. They published their research in the journal Nature Materials. From IEEE Spectrum:
"Scientists Build Vascular Network Using Sugar and a 3-D Printer"
The sugar template creates a temporary set of guiding pipes where fluid will flow. After it is printed, it is coated in a thin layer of corn-based degradable polymer to help stabilize the sugar. (Researcher Jordan) Miller and his colleagues then pour living cells around the template to encapsulate it in what becomes solid tissue. The sugar template dissolves leaving a bare vascular network through which nutrient-rich fluid can flow.