A sticky substance from the skin of frogs could be used to repair human knee joints, scientists believe.
Knee joints can be replaced
Australian researchers have already repaired torn cartilage on the knees of 10 sheep with this natural glue, which frogs use to trap insects.
They told New Scientist how it was far stronger than medical adhesives in current use.
The University of Adelaide team, with colleagues in Melbourne, is attempting to make its own version.
The glue is secreted by two species of burrowing Australian frogs of the Notaden genus that live one metre underground.
These frogs only surface during torrential rain.
At these times they are vulnerable to attack from insects.
To protect themselves they secrete a glue that gums up the jaws of the biting insects and traps them to their skin, which they later eat.
Environmental biologist Mike Tyler and his team tested the glue.
"We assumed the substance would be toxic, but when we found it wasn't, it made sense to explore it as a medical adhesive."
They found it hardened within seconds and stuck well, even in moist environments.
When set, it was flexible and had a porous structure that should make it permeable to gas and nutrients, which would encourage healing.
Mr Tyler teamed up with orthopaedic surgeon George Murrell of the University of New South Wales to test the glue in sheep with torn knee cartilage.
This cartilage, also found in human joints, acts as a shock absorber.
Knee cartilage can be damaged during sports and can be difficult to repair surgically.
Current synthetic adhesives are strong but they are somewhat toxic and form rigid, non-porous films that can hinder wound healing.
Biological glues tend to be too weak to fix parts of the body that have to withstand strong forces and wear and tear.
However, the frog glue held the damaged cartilage together well in the sheep.
A spokesman from Arthritis Care said: "This is a fascinating and encouraging development which would appear to be worthy of taking further.
"Many people with arthritis would also prefer the idea of natural substances being used in the scaffolding of a joint.
"However, only when such interventions reach the stage of being trialled among significant numbers of people will we really know whether the idea is as problem-free as it sounds."
Working with colleagues at the Commonwealth Scientific and Industrial Research Organisation in Melbourne, the scientists have characterised a key component of the glue and are now developing a genetically engineered version of this protein.
The findings were presented at a combined biological societies meeting, ComBio 2004, in Perth.