Lab-grown organs are a long-time ‘holy grail’ of organ engineering that has yet to be achieved, but new research has brought that goal a big step closer to reality using a new 3D-printing method called co-SWIFT. co-SWIFT prints branching networks of double-layered vessels that are infused with smooth muscle cells and endothelial cells into living human cardiac tissue, and can even replicate patient-specific vascular structures,indicating that it could one day be used for personalized medicine.