The concept of using 3D printing to “grow” or “build” body parts is properly referred to as tissue engineering.
This complex concept involves three levels.
1. Cells are relatively easy to 3D print. Medical science knows a lot about cells and how to make them survive and replicate them in certain conditions.
2. Tissues are considered to be collections of homogenous cells in a functional system. Presently, you can 3D print skin, which is considered an organ of the body. A few companies have successfully 3D printed liver tissue models for drug testing.
3. Organs are viewed by medical science as a collection of tissues in the right functional arrangement. To date, no one has really managed to 3D print an organ, other than as a non-functioning model. The challenges are many, but lets look at one–blood supply. How does one ensure the cells and tissues inside an organ receive the necessary blood to survive? No one has an answer yet.
Presently, the most successful tries have involved mechanical support structures, like cartilage, tendons, and ligaments. Science thinks these will be the first systems that it will be able to regenerate, but scientists are talking in terms of 15 to 20 years, maybe. It will be a long while before medical science can regenerate a heart of kidney either through lab growing methods or 3D printing.