Only a fraction of drug candidates that begin pre-clinical testing are ever approved for human use. The low success rate can be partly attributed to the differences in response between humans and the animal models currently used for testing.
Parallel to the development of 3D printing and additive manufacturing techniques using polymers and metals, another set of novel techniques has been developed that can print living biological cells. By encapsulating cells inside a gel, complex 3D structures can be printed with cells suspended throughout the structure. The cells grow and multiply within the structure, creating their own matrix and forming tissues. By using organ-specific cells generated from pluripotent stem cells, it should be possible to bioprint 3D organ-specific micro-tissues that replicate the response and functions of a human organ, but on a much smaller scale. These could be used for testing the response of human cells to drugs.