Metal oxide wire tips provide perfect surface for bone growth

Broken bones and joint replacements could heal faster, thanks to an coating for medical implants under development at The Ohio State University.

Researchers there have found that bone cells grow and reproduce faster on a textured surface than they do on a smooth one, and they grow best when they can cling to a microscopic surface made of tiny metal oxide wires.

In tests, the wires are said to have boosted cell growth by nearly 80 per cent compared to other surfaces, which suggests that the coating would help healthy bone form a strong bond with an implant faster.

The engineers have developed an affordable technique for creating the wires, which they describe in a paper in the July 2013 issue of the journal Ceramics International.

‘What’s really exciting about this technique is that we don’t have to carve the nanowires from a solid piece of metal or alloy. We can grow them from scratch, by exploiting the physics and chemistry of the materials,’ said Sheikh Akbar, professor of materials science and engineering at Ohio State. ‘That’s why we call our process ‘nanostructures by material design.’’

Akbar’s team was able to grow the wires by tailoring the mix of materials and gases inside a furnace. At temperatures around 1,300 degrees Fahrenheit, fine filaments of titanium dioxide rose from a smooth titanium surface. Each wire was found to have grown a protective coating of aluminium oxide around itself.

‘It’s strange that we don’t completely understand why this process works the way it does. We’re going to have to do some fancy microscopy to figure it out, but we do know that the wires only form under just the right conditions,’ Akbar said in a statement.

In tests, the researchers grew bone cancer cells on three different surfaces: smooth titanium, smooth titanium dioxide, and the nanowire surface.

The biggest difference in cell growth occurred within the first 15 hours of testing, when researchers measured a 20 per cent higher concentration of the bone-growth enzyme alkaline phosphatase being produced by the cells growing on the nanowires. By the end of the study, there were around 90,000 cells per square centimetre on the nanowire surface — 80 per cent more than the 50,000 cells per square centimetre on each of the other two surfaces.

Study co-author Derek Hansford, associate professor of biomedical engineering and materials science and engineering, said that the coating could aid people who have hip and knee replacements, dental implants, or broken bones that require screws and plates to repair them.

‘Our hope is that this surface treatment will become a simple-to-implement modification to titanium implants to help them form a stronger interface with surrounding bone tissue. A stronger interface means that implants and bones will be better able to share mechanical loads, and we can better preserve healthy bone and soft tissue around the implant site,’ he said.

Akbar believes that the price is right for commercial development with $100 worth of metal foil enough to make hundreds of samples.