While most 3D printers deposit melted plastic in carefully controlled positions to build up a physical model, a similar process called “bioprinting” can be accomplished with biological materials. Commercial bioprinters can cost tens of thousands of dollars or more, but as shown here you can make your own using the shell an inexpensive desktop machine. 

In this example, a Monoprice MP Select Mini V2 is stripped down to its bones and motors, subbing in an Arduino Mega and RAMPS 1.4 stepper driver board.

A syringe-like extruder is added to push out custom bioink, and the Z-axis switch mounting and Marlin firmware is modified to accommodate the new device. The homing sequence is modeled in the video below, giving a short snippet of how it works.