Tissue engineering offers new hope for damaged bodies

In as little as five years you might be able to visit your surgeon for a replacement ear or nose after injury, or a new piece of cartilage for your knee. They are coming from research into "tissue engineering", a unique blend of medicine and engineering.

The latest developments in tissue engineering were described yesterday at the British Association's Festival of Science by Dr Richard France, a lecturer in medical materials at the University of Sheffield.

"Tissue engineering is a new field employing life sciences and engineering principles to the restoration and replacement of diseased and damaged tissue," he explained.

Also known as biomaterials, the business of using metals, plastics and thread to fix broken bits is nothing new. The Romans and Chinese used gold in dental restorations as long as 2,000 years ago, Dr France said. Most of the work dates however from the end of the second World War when parachute cloth was used to replace veins. Silicone polymers are used as tracheal tubes which deliver air to the lungs and polyesters and nylons, originally used for raincoats, have been used as heart valves.

Some replacements such as artificial hip joints, represent a whole range of materials including stainless steel or titanium alloys and ultra-high molecular weight polyethylene in the cup where the metal ball joint sits. The assembly is glued into the bone end using special polymers.

The best hip joints last only 10 to 15 years, however, because the body was so very tough on "foreign" materials, Dr France said. Bone renews itself, but metal only wears and gradually degrades. The strong plastics slowly break down and the glues eventually loosen.

Much research was focused on a close examination of the "material-tissue interface", Dr France said, as a way to develop better biomaterials. This work had shown that not just the materials but the materials' surfaces also had an impact on how the body tolerated an implant.

The body's tissues also respond quite well to some materials. Bone would bond directly to titanium for example and this was now used in hips and in dentistry, he said. "The study of cells and proteins on materials is fundamental to the design of the next generation of biomaterials."

Another new approach was to find materials that could act as "scaffolds" that would support cultured tissues as they grew and then degraded and disappeared before the tissues were introduced to the recipient. This was being used to prepare both skin and cartilage cultures, he said.

Some skin products were already in use and were valuable in the treatment of burns. Scaffolds made of natural materials such as collagen were also being used in this way. Cartilage cells were first seeded onto a degradable scaffold and then cultured in a medium that contained all the nutrients needed to grow cartilage. Cartilage constructs grown in this way could be used to replace knee cartilage, he said, and clinical trials were already underway in the US for replacement nose and ear cartilage in reconstructive surgeries. Clinical application could come in five years, he said.

The goal was to use the body's own adhesion molecules and signalling molecules that would allow tissues to grow on scaffolds in much the same way they did in the body. "The challenge remains to find new ways of controlling cell behaviour and guidance on such scaffolds," he said.