The Engineer

Roughening orthopedic implants

News

Titanium and its alloys are used to make the orthopedic implants used by surgeons to repair damaged bones and joints. They are light, super strong and virtually inert inside.

But whether the implants are destined for the knee, a hip, a spine or a jaw, the silvery metal has one big drawback. Because it has a mirror surface, cells do not adhere to it very well, so implants are often roughened up before they are placed in the body.

A good way to roughen titanium is to etch nanotubes into it, since they provide a superb surface for bone cells to grasp onto as part of the healing process. But etching nanotubes in the titanium alloy is not cheap. Conventional techniques require platinum, which costs over $1,700 (£1,200) an ounce.

Now, however, through her PhD work with Prof Craig Friedrich, director of the Multi-scale Technologies Institute, Tolou Shokufar, a PhD candidate in Mechanical Engineering at Michigan Technological University, has developed a less expensive way to etch nanotubes into the titanium alloy.

In a weak solution of ammonium fluoride, she immerses two rods - one of the titanium alloy and another of copper - and hooks them up to a power source. An electrical current flows into the copper, through the solution and out through the titanium, creating a titanium-dioxide layer in the form of nanotubes about seven microns long and 100nm in diameter. Growing the ideal tube takes about two hours.

Then she applies heat and pressure to the titanium alloy, annealing the nanotubes to give them a hydrophilic, crystalline structure. The surface not only attracts water - tests show it provides a friendly place for cells to grow.

Shokufar has conducted experiments with fibroblasts - cells that make scar tissue - showing they grow faster on a layer of her titanium-dioxide nanotubes than on the unaltered surface of the titanium alloy. Next, she aims to do a similar experiment with bone-growing osteoblasts.

Because the nanotubes are chemically identical to the titanium alloy, Shokufar expects that her innovation could be approved for medical use with relative ease. It may also have a variety of other applications, ranging from drug delivery to solar cells and hydrogen generation.