It is now many years that stem cells are considered crucial for the progress of bio-engineering. A stem cell can develop to become any type of cells of our body. You take a stem cell from a person (each of us has stem cells in several places, in the bone marrow -where they are usually harvested- as well as in the blood, in vessels, in the liver and even in the brain) and you can in principle create any type of tissue by multiplying and differentiated them into a specific target. The resulting tissue is "your" tissue, since the stem cells have your imprinting all over. Transplant would no longer need drugs to stave off rejection and there would be no ethical issues (at least the ones facing us today).
Hence the interest for this paper where researchers from Tsinghua University in Beijing and Drexel University in Philadelphia describe a method they have invented to print, using a 3D printer, a sort of scaffold onto which stem cells can multiply and assume the correct spatial relation as they would do in vivo. So far the multiplication of stem cells has occurred in a bi-dimensional space, on a Petri dish, or in a volume but without any structure (they are floating in a vase).
The researchers have managed to find a way to create micro-scaffolding (see the figure, and notice that the dimension is in mm, not in cm) using a 3D printer and have demonstrated that cells multiply efficiently on that, similarly to what happens in a volume but with the advantage that the scaffold directs the resulting architecture. In practice one uses the scaffold to lead the cells to create the target tissue architecture.
I keep pointing out a variety of applications of 3D printing. It seems to me that we are really entering a new fabrication paradigm! And notice the title of the publication: biofabrication! Factories in the next decade will broaden their products types to include production of meat (the first hamburger has already been fabricated, cooked and eaten) and ... flesh.