Bone grafts could one day incorporate sea coral more extensively, thanks to a small clinical study that found refining its properties makes it more compatible and degradable than a currently used derivative.

Dr. Zhidao Xia, a specialist in regenerative medicine at Swansea University in the UK, and colleagues from the UK and China describe their findings in the latest online issue of the journal Biomedical Materials.

By partially converting calcium carbonate found in sea coral, they made a biodegradable composite material called coralline hydroxyapatite/calcium carbonate (CHACC) - comprising "a coral calcium carbonate scaffold enveloped by a thin layer of hydroxyapatite."

In a small trial, they found this material showed promising results in bone grafts in 16 patients.

They observed bone healing in each of the patients after 4 months, and after 2 years, the CHACC had fully biodegraded.

The researchers say the new material is superior to coralline hydroxyapatite (CHA), from which it is derived. CHA, which is commercially available, is already used in bone grafts, but its use is limited to specific bones because it does not fully biodegrade.

Dr. Xia comments:

"Our methods have considerably improved the outcome of bone grafts by using the partial conversion technique, in which the biodegradable composition from natural coral is reserved. It works in a very similar way to commercially available CHA for conductive bone regeneration, but the better biodegradation properties are compatible with the host tissue's natural bone turnover process."

Partial conversion technique offers improvement

Dr. Xia explains that when biomaterials do not fully biodegrade, they stay in the bone tissue and can cause problems. In some extreme cases this can lead to a new fracture or bacterial infection.

The team also suggests CHACC could be a promising alternative to autografts, where pieces of bone from another part of the body are used to grow new bone. Autografts are not ideal because there is a limited supply of source material, and the bone removal can be painful and cause long-term impairment.

For their study, the team used coral from the sea around South China and partially refined the calcium carbonate found in its exoskeleton into CHA to make CHACC.

The CHACC they made contained 15% CHA in a thin layer around the calcium carbonate. This provides a strong and porous structure, which is what makes CHA a successful bone grafting material, but it also offers a more biodegradable, bone-compatible overall product.

After testing the new material's physical and chemical properties, the team populated pieces of it with human mesenchymal stem cells and implanted them under the skin of lab mice.

After 10 weeks, they could see new bone had formed on the surface of the implanted CHACC.

The researchers then tested the CHACC in a small trial of 11 male and 5 female patients, who between them had four different kinds of bone defects.

The results showed not only that within 4 months bone healing took place around the implant sites, but also the CHACC implants themselves degraded after 18 to 24 months.

'Promising results,' but still more work to do

The timing of biodegrading is an important factor in bone grafts. After a fracture, it can take up to 5 years for bone remodelling (where old bone is totally replaced with new tissue) to complete.

So an ideal biomaterial is one that degrades within the natural bone remodelling cycle, but not too early so as to deny the regeneration a structure to model around.

The researchers point out this is still early days, and there is a lot of work to do before the biomaterial is up to the standard of an autograft, as Dr. Xia explains:

"Although our study has provided promising results, the CHACC material does not contain a bone organic matrix, living cells and the ability to induce, rather than conduct, new bone formation.

Therefore, our future work is to combine controlled growth factor delivery and stem cell technology in order to develop an even better solution for bone graft materials."

In September 2012, US researchers reported finding that the odds of successful grafts improved by resurfacing bone in a new way.