More than 8 million surgical procedures are performed
in the United States each year to treat organ failure and tissue loss.
The emerging discipline of tissue engineering offers an alternative
to surgery.
Tissue engineering aims to either stimulate the body
to regenerate tissue on its own or, depending on the type of injury,
to grow tissue outside the body that can then be implanted as natural
tissue. This means that ultimately the body can heal itself, vastly
improving the treatment options for numerous injuries and illnesses.
Christine Schmidt, the T. Brockett Hudson Fellow
in the Department of Biomedical
Engineering at The University of Texas
at Austin, is a leader in the field.
Her research focuses on the nervous system and the
vascular system.
Working with the nervous system has long been a challenge
for doctors and scientists. The system is complicated, and individual
nerve structures themselves are very long. Yet paralysis due to nerve
debilitates 11,000 Americans each year.
“All the nerves in your body basically have
their origins in the spinal cord,” Schmidt says, “so they’re
either on the outside of your spinal cord or very near it, and that’s
how they interface with the brain and allow you to coordinate all
of your activities.”
Currently, the only hope for repairing severely damaged
nerves is by removing a healthy, but less essential, nerve from another
part of the body and grafting it to the damaged area.
Schmidt’s research centers on implanting biomaterials
that encourage the body to regenerate nerves on its own.
“When
you have a large defect in the nerve, what happens is when these
fibers are regenerating, or trying to regenerate, they go all over
the place,”
she says. “They can’t find where they are supposed to go. Here
we need to physically say, ‘You need to go to this muscle target,’
physically
providing that directionality, and also providing cues that will
stimulate predictable growth.”
Schmidt has developed an electricity-conducting polymer
that, in collaboration with a sugar molecule found in blood vessels
and most tissues, can stimulate new growth in peripheral nerves. Hollow
tubes made of this polymer bridge gaps in damaged nerves. Once in
place, the sugar in the tubes slowly starts to break down, releasing
substances that encourage the growth of new blood vessels, which in
turn help the nerve to re-grow within the tube. In a period of two
to six weeks, the tube itself disintegrates, leaving only the patient’s
own new nerves.
Electrical current has been proven to have a beneficial
effect on nerves, so it can also be used in the repair process. The
hope behind this research is that peripheral nerve regeneration can
be improved and that eventually the regeneration of the spinal cord,
where the most debilitating of injuries occur, will be possible.
Schmidt’s approach to vascular regeneration is to
create a vascular prosthesis that could be used in coronary bypass
procedures. Cardiovascular disease is the leading cause of death in
the United States, and over 1.4 million surgeries are performed each
year.
Coronary bypass requires that a blood vessel be transplanted
from elsewhere in the patient, usually from a leg, and used as a graft
to bypass blocked arteries. In collaboration with Sulzer Biologics,
an Austin-based biomedical company, Schmidt and her researchers are
developing in the lab a way of growing living tissue that will ideally
behave like a normal blood vessel when implanted into the body.
This process a biomaterial scaffold. A needle would
draw a small sample of blood vessel cells and grow the cells in large
numbers. Then those cells would be combined with a physical structure
to grow a living blood vessel. The new blood vessel could be used
in the coronary bypass, which would reduce the need for additional
surgeries in patients, hasten healing, and lessen the long-term side
effects of bypass surgery.
It may take a decade or more, however, before the
technologies she is developing are used in hospitals. Schmidt says
that while they have had some “very encouraging animal studies,” the
technology has not yet gone through clinical trials in humans. After
more animal studies, they will seek a company sponsor to supply the
funding and facilities for clinical studies and begin pursuing FDA
approval.
Some practical examples of tissue engineering products
are starting to appear on the market. A skin product already exists,
and a cartilage product should be available soon. Another company
is doing clinical trials on a collagen-based tube for use in repair
of very small nerve defects. Schmidt points out that scientists and
biomedical companies are beginning with the simplest structures in
seeking FDA approval, and that more complicated devices, especially
those with biochemical components, are much more difficult to be approved.
