Bio-Active Prosthetic Joints for More Successful Implants

An unsuccessful joint replacement will cause pain, immobility and a progressively unstable hip or knee – for example – that needs repeat surgery. The EU-funded project BIOSTEM has developed a coating for artificial joints to improve the chances of stability and avoid these symptoms that threaten patient quality of life.

The current treatment for osteoarthritis is to replace the affected joint with an implant. More than 270 000 knee and hip replacements are carried out annually in the UK alone. Unfortunately, the device sometimes fails to integrate with the bone, which may already be compromised by diseases such as osteoarthritis (OA).

Credit: © georgerudy- fotoloia.com

The answer is to make the implant ‘biologically active’ so that after integration, the bone and the implant behave more like one entity. “Coating with a biological material that will promote bone formation should encourage ‘osseo’ or bone integration,” says Mary Murphy, scientific project leader within BIOSTEM.

Surface treatment

Coating the implant is one way to improve implant success. Previous research has shown that the surface properties strongly influence the fate of the implant and whether it is likely to become unstable or not. The BIOSTEM team has modified poly-(ether-ether)-ketone (PEEK) as a coating for metal implants. PEEK is a type of hard plastic with a success record in surgery on the spine as well as face and skull. Its drawback for joint replacement is that it is biologically inactive.

Modified collagen was therefore added to the PEEK; found naturally in bones, muscles and skin, collagen forms a scaffold to provide strength and structure. To complete the recipe, mesenchymal stem cells were added. These can produce bone cells to increase osseointegration.

The project has also tested a novel device to apply the coating that bombards the outer surface of PEEK with a gas containing the collagen. The molecules of collagen react with the destabilised outer area and become incorporated into the PEEK. The machine will fit on a lab bench and can therefore be used directly where it is needed – in the hospitals carrying out operations.

Promising trials

Preclinical trials on rabbits with PEEK implants are almost complete. The mechanical testing produced good results, indicating increased osseointegration.

Examination of the joints at molecular level after removal also proved encouraging. Protein modification indicated that the collagen component of the coating had been incorporated and there were positive effects on the potential of stem cells to form bone.

The team is optimistic that further optimisation of the coating with the addition of growth factors will add to these promising results, and expects additional improvements in implant quality. “Specific growth factors are required for generation of new bone and will increase osseointegration without potential side effects when localised to the area where they are needed,” Murphy explains.

The future for total joint replacement

Incidences of OA and the associated need for joint replacements will rise as the average age of the population increases. More critical is the rise in the number of younger people receiving joint replacements due in part to high-impact activities such as running. Murphy sums up the potential success of BIOSTEM research. “PEEK wears well and producing biologically active PEEK will increase osseointegration of joint implants to decrease the need for costly revision surgeries.”

Young researcher input

Jessica Hayes, the fellow involved in the BIOSTEM project had just finished her PhD in surface modification for titanium implant removal for paediatrics when she was recruited for this Marie Curie Intra-European Fellowship for Career Development.

“Involvement in this successful programme has certainly contributed to my subsequent achievements, such as becoming a Lindau Fellow, and my future involvement in a Horizon 2020 project, AUTOSTEM,” she says.