Complex sentence: In 2013, the company Organovo produced a human liver using 3D bioprinting, though it is not suitable for transplantation, and has primarily been used as a medium for drug testing.
Split into simpler sentences: In 2013, the company Organovo produced a human liver using 3D bioprinting. However, it is not a suitable transplant organ, and has primarily been used as a medium for drug testing.