Metal in Motion
UMaine researchers find that, when it comes to bone repair, foam metal may be just what the doctor ordered

About the Photo: UMaine engineer Darrell Donahue will use specialized equipment to measure the strength and efficacy of foam metal implants.

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At first glance, it's hard to imagine the drab lump of hardened metallic froth held by reconstructive surgeon Dr. Ian Dickey as any-thing important, much less a medical breakthrough. But placed inside the human body, it could be a wonder to behold.

The lightweight, pored material is a sample of foam metal. From aluminum-ceramic sleeves to sponge-like titanium discs, foam metals have been used in industrial applications for decades, primarily as insulators and filters. Working with Professor of Chemical and Biological Engineering Darrell Donahue and a team of other University of Maine researchers, Dickey is testing the potential of foam metals in medicine, and the preliminary findings have been nothing short of astounding.

"The results of our initial studies have been outstanding. Not only does one get bone growth into the material, but we had soft tissue ingrowth as well," says Dickey, who began a collaboration with Donahue in 2004 that examined the strength and compatibility of foam metal implants in animals. "This level of compatibility with an implant is really exciting. We haven't seen anything that works like this."

Because of the body's natural resistance to foreign materials, implants used for bone repair have been fraught with difficulties. Slow recovery times, costly and painful second surgeries, and imperfect results often leave patients less mobile and more prone to future complications. In most cases, the problems associated with medical implants like replacement hips and bone-strengthening pins have to do with compatibility — the body's tissues recognize the implant as foreign and treat it like any other invader, walling the implant off from the living cells for protection. Because no biological connection is established between the living and nonliving material, traditional implants are often weak and prone to infection.

Without the possibility of real, biological attachment between the implant and live tissue, scar tissue can form.

Tests have shown that foam metal washers used for repairs at the rotator cuff can be stronger than other surgical repairs at four weeks and as strong as a normal joint by six weeks. At 30 months, the attachments not only stayed strong, they were 20 percent stronger than a healthy, uninjured joint.

The added strength comes from the living bone and soft tissue growing in the porous structure of the foam metal, fed by tiny blood vessels that also form inside the implant. Where traditional implants caused the formation of scar tissue that weakened the repair, foam metal implants provide a kind of biological scaffolding for new tissue growth.
 

Dickey was conducting research at the Mayo Clinic in Rochester, Minn., when he started working with Donahue, an expert in bone biomechanics. The collaboration eventually brought Dickey to Eastern Maine Medical Center in Bangor.

As their research into medical uses for foam metals continued, Donahue and Dickey tapped into additional resources at UMaine, recruiting Scott Collins of the Laboratory for Surface Science and Technology (LASST), Anja Nohe and Michael Mason of the Department of Chemical and Biological Engineering, and Andre Khalil of the Department of Mathematics and Statistics. Their ultimate goal is not only to prove that foam metal implants work, but to find out why.

"My role in the project is relatively simple, but it's critical to understanding how well the implant interfaces with living tissue," says Mason, who, together with Khalil, is conducting a highly specialized mathematical analysis of foam metal samples that have been used as experimental implants. "Our goal is to develop reliable image analysis tools so that we can determine how the tissue responds to pore size, surface coatings and other factors. The challenge is finding methods that can separate the biological material in the image from the foam metal substructure."

Just down the hall from Mason, Nohe is applying her expertise in biological systems to develop new ways to test engineered samples in vitro, allowing the team to look at tissue growth in foam metal in a more precisely controlled laboratory environment. More effective methods for culturing tissue in foam metal samples will facilitate quicker, more reliable analysis of test samples and implant prototypes.
 

While Mason, Khalil and Nohe perfect new methods for testing foam metal samples and interpreting research data, Collins is manipulating the material itself, creating precisely engineered versions of foam metal implants to help determine how different physical characteristics in the metal affect its ability to integrate with living tissue.

"They needed to control the geometry of the pores down to the nanometer scale," says Collins. "By creating the material in a very controlled way, we can help determine whether the growth of tissue into the holes is a function of the length or the diameter of the pores, and we can also gather information on the topology of the surface and other characteristics so that they can set up manufacturing of the material accordingly."

Together, the researchers are developing a high-tech tool kit for the study of foam metals in an effort to better understand what makes the material so effective as a medical implant. Their discoveries will help foam metal manufacturers to develop a new line of products that will improve patients' lives.

Drawing on the energy, experience and equipment available through LASST, the Institute for Molecular Biophysics and other resources, the research team is pursuing public and private funding that could expand their research efforts. Foam metal projects also are being considered for UMaine internal R&D funding as an area of new and emerging research benefitting the state.

UMaine could take a leadership role in this area of medical technology akin to what has been done in pulp and paper research, says Dickey, an adjunct professor in UMaine's Department of Chemical and Biological Engineering.

"This stuff rebuilds bone. How often does a new technology come along where the initial data on its use is so overwhelmingly positive?" Dickey says. "We have an amazing opportunity to become a leader in foam metals research, not just with one project or with one material; we could define the whole genre."

By David Munson
September-October, 2006

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