An unusual “nanowire” coating for medical implants may soon be helping broken bones and joint replacements to heal faster.

Ohio State University reports that research engineers there have found that bone cells grow and reproduce almost twice as fast on a textured surface made of metal oxide wires, each tens of thousands of times thinner than a human hair.

The engineers have developed an affordable technique for creating these wires, which they describe in a paper in the current issue of the journal Ceramics International. The research suggests that the coating could help healthy bone form a strong bond with a metal implant.

The Ohio State University team call their process “Nanostructures by material design.”

Sheikh Akbar, professor of materials science and engineering at Ohio State, explains:

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.”

Co-advised by Suliman Dregia, associate professor of materials science and engineering, Prof. Sheikh Akbar’s team has been 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.

The rise of the fine filaments was expected, but what happened next was not. Each wire began to wrap a protective coating of aluminum oxide around itself – like a layer of bark around a tree trunk. This would have made sense if the scientists had been working with a titanium alloy that contained aluminum. But they were working with pure titanium, so it is not clear how this aluminum coating formed.

“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,” Prof. Sheikh Akbar said.

In tests, the researchers grew bone cancer cells on three different surfaces: smooth titanium, smooth titanium dioxide, and the nanowire carpet. They chose cancer cells because they are particularly hardy, and also reproduce in the same way healthy bone cells do.

The biggest difference in cell growth occurred within the first 15 hours of testing, when researchers measured a 20% higher concentration of the bone-growth enzyme alkaline phosphatase in the cells growing on the nanowires. By the end of the study, there were around 90,000 cells per square centimeter on the nanowire surface – 80% higher density than on 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 for repair.

Derek Hansford said:

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.”

Prof. Sheikh Akbar believes that the price is right for commercial development. Around $100 worth of metal foil provides enough material to make hundreds of samples. The method could hardly be simpler – set the right mix of materials and gases in a laboratory furnace, press the ‘On’ button, sit back and wait.

“Seriously, if you spent the day in my lab, you could learn how to do it yourself,” Prof. Sheikh Akbar said.

His team are now exploring other material and gas combinations to make different nano-sized shapes for cell growth and chemical sensing in a program partially funded by the US National Science Foundation.