The lung-on-a-chip device mimics a human lung and allows living tissue to be studied without opening up people or animals

Scientists have grown lungs in the laboratory, a major first step towards growing tissue that could one day be used to replace diseased or damaged human lungs.

In one study, scientists at Harvard Medical School and the Children's Hospital in Boston created a device that mimics a human lung, by incorporating lung and blood vessel cells into a microchip (see video, above). Meanwhile, at Yale University, scientists have grown lung tissue that carries out some of the basic functions of the organ, including exchanging oxygen and carbon dioxide.

Both studies are published today in the journal Science.

The work at Harvard will be used mainly for studying the workings of living lung tissue without having to open up people or animals. It could also be used to test the effects of environmental toxins or new drugs.

The lung-on-a-chip could predict how human lungs absorb airborne nanoparticles and mimic the inflammatory response triggered by pathogens, said Donald Ingber, the vascular biologist who led the work at Harvard University's Wyss Institute. "Organs-on-chips could replace many animal studies in the future," he added. "We really can't understand how biology works unless we put it in the physical context of real living cells, tissues and organs."

The device was able to replicate many of the natural responses of lung tissue, such as detecting pathogens and speeding up blood flow so that immune cells can deal with the invaders.

The Harvard team is working on building other organ models, including ones made from gut, bone marrow or cancer cells.

The Yale scientists, led by Laura Niklason, started with lungs from adult rats and removed the cells, leaving behind only the network that supports the branching airways and blood system. This support network was later used as a scaffold to grow cells for a new lung, which was implanted into rats for up to two hours at a time.

"We succeeded in engineering an implantable lung in our rat model that could efficiently exchange oxygen and carbon dioxide, and could oxygenate haemoglobin in the blood," said Niklason. "This is an early step in the regeneration of entire lungs for larger animals and, eventually, for humans."

To make the technology work for humans will take several more years of work using stem cells to grow the complex structures required for a fully-funtioning organ, said Niklason.