`Sponge' mends broken bones

FOOTBALLERS MIGHT kill for it; their trainers will clamour for it. For scientists have developed a "magic sponge" that really does seem to help mend broken bones.

The "sponge" is made from cow collagen, the same material as ligaments, and impregnated with genes that promote bone growth. It can be implanted into the fracture to encourage recovery. Tests on dogs have been encouraging, say scientists at the biotechnology company Selective Genetics in San Diego, California.

If the technique can be extended to humans it would have an immediate application in the elderly, where hip fractures often leave otherwise healthy people immobile.

The American tests, reported today in the journal Nature Medicine, involved a "gene activated matrix" (GAM) containing mobile loops of DNA called plasmids. These contained a gene that leads to the promotion of bone growth.

The team inserted the gene-carrying sponge into the broken bones of three dogs and measured the bone density by X-ray. Fractures usually take six weeks to heal. In the experiments, by two to six weeks after implantation there was an increase in new bone formation at the fracture site compared to fractures without the GAM.

The technique overcomes many of the stumbling blocks associated with gene therapy. In theory, adding extra genes could compensate for flaws in an individual's DNA or - as in this case - provide a boost for processes already underway.

But repeated problems include getting the new genes incorporated into the host's DNA, and getting them to work only where and when needed.

The plasmid method shows promise because the additional genes are restricted to the site where they are needed.