How it Works
Science has come a long way from what it was and now, we are able to print, in other words "biofabricate" human tissues and bones. This term of "printing" however is indirect, as in we don't actually print the tissue/organ. Rather, we print scaffolds that build a structure that guides the cells in its regrowth. The procedure for bone fabrication is different than the process for tissue.
Bone Fabrication
Bone Fabrication has been further advanced and researched on in comparison to Tissue Fabrication. The steps of bone fabrication are much simplier than tissue fabrication.
In the video above, it goes over the usage of a 3D printed scaffold that creates the structure for the bone as it regrows. The dimensions of the injury would be scanned and 3D printed into a scaffold. That scaffold would then be transplanted into the patient's injury and their stem cells would be injected among the structure of the scaffold so that it would grow back in a natural and perfected shape. The scaffold structure, being made of natural polymers would then disintegrate away with no chemical harms.
Tissue Fabrication
Tissue Fabrication has become a reality, however, only for rats. In the near future, biofabricated whole organs should be on their way. Scientists have proven that biofabricated organs can be real.
Tissue Fabrication does not use scaffolds as the video above explains. However, what it does use would be "bio-inks" which contain cells, protein, and such. The bioinks would then be dispensed in a certain structure/spot by the 3D printer in specific amounts. This is later on cultured slowly and they become vascularized networks that leads to the growth of actual organs. Many 3D printers are made specifically for this purpose as researchers and scientists are starting to experiment on making whole, biofabricated organs possible.