The process of using cells to grow new body parts that can be used as natural prostheses is called regenerative medicine or tissue engineering.

Here's a breakdown of the terms:

* Regenerative medicine focuses on the repair or replacement of damaged tissues or organs through the use of stem cells, growth factors, and biomaterials.

* Tissue engineering is a subfield of regenerative medicine that focuses on creating tissues or organs in vitro (in a lab) using cells, biomaterials, and bioreactors.

Both terms encompass the concept of using cells to grow new body parts, which can then be used as natural prostheses.