Coating: Replacements Bond Jointed Better with Bone


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

Researchers here 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 shag carpet made of tiny metal oxide wires.

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

"What is really exciting about this technique is that we do not 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. "That is 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 was tens of thousands of times smaller than a human hair.

But then something unusual happened that the engineers could not explain. Each wire grew a protective coating of aluminum oxide around itself — like a layer of bark around a tree trunk. The growth of the coating might make sense, if the material in the furnace were a titanium alloy that contained aluminum. But in this case, the researchers were working with pure titanium, so it is not clear how the wires grew an aluminum coating.

"It is strange that we do not completely understand why this process works the way it does. We are 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 tests, the researchers grew bone cancer cells on three different surfaces: smooth titanium, smooth titanium dioxide, and the nanowire carpet. They chose the cancer cells because the cells are particularly hardy, and also reproduce 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 percent 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 centimeter on the nanowire surface – 80 percent more than the 50,000 cells per square centimeter on each of the other two surfaces.

"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," study co-author Derek Hansford said.; Source: The Ohio State University