The tiny lab-grown livers that perform like the real thing... and could pave the way for human-sized organs for transplant Scientists used a 3D printer loaded with cells to create mini livers Can be infected with a disease to observe its progress through organ Tiny livers can also be used to monitor effectiveness of drugs Scientists working towards developing laboratory-grown livers for transplant have managed to create mini versions of the organ using a 3D printer. Just half a millimetre deep and four millimetres wide, the tiny livers are capable of performing many critical functions of the real thing; including producing proteins responsible for ferrying hormones, salt and drugs around the body. California-based bio-printing pioneers Organovo created the mini organs by using the machine to build up around 20 layers of liver cells - along with cells from the lining of blood vessels to nourish the liver cells with nutrients and oxygen. Multi-cellular: Scientists at Organovo, in San Diego, California, used bio-printing to build up layers of the cells that make up the liver in a lab The crucial addition of blood vessel cells means the 3D, multi-cellular tissue can survive for five days or more. This is in contrast to 2D cultures, based on single or double layers of cells, which only last two days and don't have the extent of functions as Organovo's new mini-livers. Detoxification: The mini-livers are capable of performing many of the vital functions of the real thing, including producing key proteins and cholesterol Ultimately Organovo is working towards developing human-sized versions suitable for transplant. Its mini-livers are capable of producing the key protein albumin as well as cholesterol and crucial detoxification enzymes - cytochrome P450s - that metabolise drugs in the liver, a report on newscientist.com said. The realistic structure and function of the mini organs - combined of layers of hepatocytes and stellate cells - has positive implications for research in that they can infected with a disease to observe its progress, or treated with a drug to monitor its impact. The liver is responsible for filtering the blood, metabolising and transporting drugs, and producing an array of proteins that are vital to homeostasis. A number of genetic disorders are linked to the reduction of absence of proteins that would usually be produced by the liver. Now researchers at the San Diego laboratory will be working on printing larger branched networks of blood vessels that could nourish a human-sized version of the structure. The firm unveiled the mini-livers at the Experimental Biology conference in Boston this week. Organovo has pioneered the bio-printing, which creates living human tissues that mimic the form and function of native tissues. The machine works by using two print heads; one of which lays down a scaffold, while the other places human cells into the shape of the organ that is being formed. In the case of the mini-livers, the cells used come from spare tissue removed in operations and biopsies. 3D printers allow objects of any shape to be created from just a digital file. They work in an extremely simple way, by building up a 3D object from layers of material. Like a traditional inkjet printer, material, usually plastic, is laid down on a base. Further layers are simply printed on top, gradually revealing a 3D object. The technology is used in a huge range of industries from construction to aerospace. Shoes, jewellery and even dresses have been created, with designs often sold online. Many believe it could even lead to 'mini factories' for living rooms allowing consumers to print anything they want - from a bracelet to a replacement part for a broken household appliance.