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:
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
Without the possibility of real,
biological attachment between the implant and live tissue, scar tissue
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
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
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