Dr. Jennifer Lewis, a 2016 Vannevar Bush Fellow, along with fellow Harvard researchers, has developed a technique for 3D-printing vascular channels into stem-cell-derived 
organ building blocks. The technique is called SWIFT (Sacrificial Writing into Functional Tissue), and uses gelatin to create the required channels in each organ building block. Tests of the technique found viable, contracting heart tissue whose contractions mimicked its human counterpart. Collaborations are underway to implant these tissues into animal models and explore their host integration.
For more, see: https://news.harvard.edu/gazette/story/2019/09/new-technique-being-developed-to-therapeutically-repair-and-replace-human-organs/