This means that if a drug is going to have an adverse effect on any part of the body, chances are it will be the liver. It would seem to follow, therefore, that if a pharmaceutical company wanted to test the safety of its products, it would be nice to have some miniature human livers on which to experiment – which is just what San Diego-based biotech firm Organovo is about to start selling.

Known as exVive3D, the three-dimensional liver models measure just a few millimeters across, and are created using a 3D bioprinter. The device incorporates two print heads, one of which deposits a support matrix, and the other of which precisely places human liver cells in it.

The resulting models are composed of living human liver tissue, and incorporate hepatocytes, stellate, and endothelial cells – just like a real, full-sized liver. They also produce liver proteins such as albumin, fibrinogen and transferrin, plus they synthesize cholesterol.