Bone-making 'bioreactor'

Scientists have grown living bone tissue inside the body for the first time in a development that could revolutionise reconstructive surgery using bone transplants.

The researchers have grown fresh layers of bone on existing healthy leg bones. They have then transplanted this tissue successfully to mend damaged bones in other parts of the body.

The research has been carried out on laboratory rabbits, but the scientists believe they will be able to perform similar operations on human patients to repair serious injuries.

If the research can be replicated, it raises the possibility of exploiting the body's own bone-making capacity to produce fresh bone for transplanting back into the same patient.

As well as providing a new and abundant source of fresh bone tissue, the technique of self-transplant surgery would minimise the risk of introducing infections and would overcome the need for the patient to take tissue-rejection drugs.

Molly Stevens of Imperial College London, who was part of the international team of scientists who carried out the research, said that the breakthrough is one of the most important developments in the field of bone regeneration for many years.

"We're really excited because it deviates so much from the previous approaches and the results are so much better," Dr Stevens said.

Bone surgery is seriously hampered by the lack of fresh bone tissue for transplants. The conventional approach is to take small pieces of bone from the patient's hip or ribs, but the amount of bone that can be taken in this way is limited and the procedure is painful and risky.

A more revolutionary approach is to grow bone artificially in the laboratory but again this has proved disappointing. The amount of bone that can be grown is limited, and its internal structure is weak.

The latest technique is to grow new bone inside the body using the inherent bone-growing tissue - a thin membrane that surrounds the bone called the periosteum, which contains the vital stem cells of the bone.

The scientists injected a sterile saline solution underneath the periosteum to create a small fluid-filled cavity between the membrane and the surface of the bone. They then injected a special gel containing calcium, which stimulated stem cells in the periosteum to produce layers of fresh bone tissue within the cavity.

Prasad Shastri, assistant professor of biomedical engineering at Vanderbilt University in Nashville, Tennessee, said the process is akin to creating a miniature "bone bioreactor" inside the body.

"We have shown that we can grow predictable volumes of bone on demand. And we did so by persuading the body to do what it already knows how to do," Professor Shastri said.

It was relatively easy to peel away the freshly grown layers of bone without damaging the tibia or shinbone beneath and then transplant these bone fragments to repair damaged bones, Dr Stevens said.

"The new bone actually has comparable strength and mechanical properties to native bone, and since the harvested bone is fresh, it integrates really well at a recipient site," she said.

The study, which is published in the journal Proceedings of the National Academy of Sciences, has already formed the basis of an application to an ethics committee for human trials.

It is also being studied with a view to adopting a similar approach for the engineering of fresh liver and pancreatic tissue, organs that also have outer layers similar to a periosteum, said Professor Robert Langer of the Massachusetts Institute of Technology in Boston. He was also part of the research team.

"The research has important implications not only for engineering bone, but for engineering tissues of any kind. It has the potential for changing the way that tissue engineering is done in the future," Professor Langer said.

It took six weeks for new layers of bone to form in the rabbits and another 12 weeks or so for the transplants to fuse with and repair the damaged bones.

Bone surgery

* Conventional approach: Take small pieces of bone from the patient's hip or ribs (small amounts of bone only, painful and risky).

* Laboratory: Grow the bone artificially in the lab (amounts still limited, internal structure of bones are weak).

* Latest technique: Grow new bone inside the body using tissue (plentiful supplies of bone and little risk of infection but not yet tested on humans).

- INDEPENDENT