Better Artificial Body Parts With Metal Nanobumps

By Roland Piquepaille

They based their theory on a simple fact. Surface bumps on conventional alloys used in prostheses are in the micron range, while they are ten times smaller in natural bones, around 100 nanometers. They thought a reduction of the size of these bumps in the prostheses would also reduce the risk of rejection by the body.

Thomas Webster, an assistant professor of biomedical engineering, and postdoctoral researcher Jeremiah Ejiofor, have shown that materials containing the nanometer-scale bumps could be critical to keeping the body from rejecting artificial parts.

"We believe the bone cells are basically recognizing the rougher nanometer surface and saying, 'Gee, this is a lot like what I'm used to adhering to in the body, so I am going to adhere to it and make bone,'" Webster said.

Here is how they proceeded.

The experiments -- in a field of research known as tissue engineering -- were done in petri dishes, not with animals or people. Webster had demonstrated similar increases in cell growth using ceramics and various polymers, or plastics, and composites made of both ceramics and polymers, which are used in artificial body parts.

Their results were pretty spectacular.

Webster and Ejiofor combined nanometer particles of a titanium alloy with a liquid suspension of human bone cells in petri plates. After three hours, they washed the alloys and used a microscope to count how many of the dyed cells adhered, which enabled the researchers to calculate how many cells stuck to the metal. Out of 2,500 bone cells in the suspension, about 2,300 -- or more than 90 percent -- were found to adhere to the metal. That compares with about 1,300 cells -- or about 50 percent -- adhering to metal with conventional, smoother surfaces.

So for now, research is limited to petri dishes. And several years will pass before improved artificial hips come to market. But the needs are growing.

For example, about 152,000 hip replacement surgeries were performed in the United States in 2000, representing a 33 percent increase from 1990. The number of hip replacements by 2030 is expected to grow to 272,000 in this country alone because of elderly baby boomers.

They presented their results on October 28, 2003 at the Nanoparticles 2003 Conference held in Boston. Here is the abstract of their presentation, "Nanoparticulate Metals: Promising Biocompatible Materials For Orthopedic Applications."

Most current implants for total bone replacement or their fixations are made out of metals. They have mechanical properties suitable for the specific bone clinical therapy, but have been shown to fall short of long-term compatibility with bone tissue and bodily fluids. Materials analyses showed that the crystal grain size of majority of these implants are in micrometer range, unlike the nanometer size dimensions of body macromolecules such as proteins and "stem" cells. This work attempts to develop new biocompatible materials with nanometer grain sizes, capable of increased mechanical properties, improved and sustained biofunctions of the boneforming cells. Alloy design, process design and in vitro cellular characterizations of these formulations yield significant improvements, a finding that identifies the substrates as promising scaffolds or fixation components in orthopedic applications.

Source: Emil Venere (writer) and Thomas Webster (source), Purdue University, November 3, 2003