Thousands of patients could avoid painful knee replacements after scientists developed a material to help cartilage regrow.

The 'bouncy bio-glass' mimics the structure of cartilage and can be 3D-printed to fit precisely into damaged areas and stimulate new cell growth.

Cartilage - the flexible connective tissue found in joints and between vertebrae in the spine - is difficult to repair.

At the moment, surgeons can create scar-like tissue to help fix damaged cartilage, but most patients end up needing their joint replaced with metal and plastic parts anyway.

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Using the new material, scientists can create a tiny biodegradable 'scaffold' and implant it into a damaged area to encourage existing cartilage cells to grow through microscopic pores in the bio-glass.

Over time, the scaffold degrades naturally and safely in the body, leaving fresh cartilage in its place. Bio-glass, which is based on silica, has been used since the Vietnam War to help regrow bones.

But researchers from Imperial College London and the University of Milano-Bicocca in Italy have adapted it for joints.

They added the plastic polycaprolactone, which keeps it strong but makes it flexible and shock-absorbing like cartilage.

They were able to 3D print the material into structures that encouraged cartilage cells from the knees to grow in test tubes.

Within ten years they hope to use the technique in surgery, which could prevent thousands of people with damaged cartilage from needing knee replacements. Professor Julian Jones, of Imperial College London, said the technology could ultimately provide relief to people around the world.

He added: "Patients will readily attest to the loss of mobility associated with degraded cartilage, and the lengths they will go to try and alleviate often excruciating pain."

The technique is expected to help young people with sports injuries, or older people whose cartilage is wearing away from osteoarthritis.

Professor Jones added: "It is particularly good if you have got some damaged cartilage and you want to help it back to its original form. Most knee replacements are due to osteoarthritis, which is general degradation of cartilage over time. This could prevent that."

But he warned that the material would not work if all the cartilage had eroded away, so it is important that conditions such as arthritis are diagnosed before it is too late.

The researchers also developed synthetic cartilage discs from the bio-glass, which could be used to treat patients with slipped discs or damage to cartilage in the spine.

Bio-glass discs are flexible and could replace current treatments which involve fusing the vertebrae together with metal and plastic, reducing patients' mobility.

But the synthetic discs are not thought to be suitable for knees and hips because of the way the body's weight is distributed through these joints.

Dr Natalie Carter, of Arthritis Research UK, said: "This is truly exciting research. There are ten million people living with the pain of arthritis or a severe musculoskeletal condition in the UK. There is potential for this to transform their lives."