Combat
Injuries: Regenerating the Nerves
[ Sound familiar? = Bio-Engineered Synthetic nervous system -- MC ]
Summary
When it comes to research on regenerating
nerve cells Mayo Clinic is taking point for the U.S. military. The research
team is part of a national consortium aimed at restoring mobility to severely
injured American combat veterans. The solution involves special growth
factors, dissolving polymers, and stem cells to reconnect and restore feeling
to the nervous system.
If there is any kindness at all in
war it is derived from the push it gives medical science to explore novel
ways of treating wounded service men and women. This impetus in part is
integral to a new medical emphasis known as regenerative medicine. Mayo
Clinic researchers are in the vanguard of this field with collaborative
efforts leading to innovations to aid in the regeneration of peripheral
nerves and bone that has been damaged in warfare.
The good news about Iraq and
Afghanistan war injuries is that well over 90 percent of wounded service men
and women survive. In contrast, only a quarter of wounded soldiers in Korea,
Vietnam and the Gulf War died from their injuries. The majority of injuries
in the Iraq and Afghanistan conflicts affect the arms and legs because
improved Kevlar body armor has lessened damage to the head, chest and
abdomen. The armor was tested for use on arms and legs, but soldiers rejected
it, as it reduced their mobility and quick access to their weapons.
The bad news?
“They survive with really serious
injuries, which can be life-changing,” says Michael Yaszemski, M.D., Ph.D., a brigadier general in
the U.S. Air Force Reserve, who has deployed to Iraq and served as deputy
commander of the theater hospital at Balad Air
Base, north of Bagdad. Dr. Yaszemski is also a Mayo
Clinic orthopedic surgeon and biomedical engineer. Dr. Yaszemski
and collaborator Anthony Windebank, M.D., Mayo neurologist and molecular
neuroscientist, are co-directors for nerve injury research in AFIRM
— the Armed Forces Institute of Regenerative Medicine. AFIRM was created
and funded by the Army, Navy and the National Institutes of Health to focus
on new treatments for war wounded. The consortium of 16 institutions has been
granted $85 million over five years to achieve its goals.
Dr. Yaszemski
has personally cared for patients in the field that he is now trying to help
in the lab. “In using synthetic polymer scaffolds as our core, we are
engineering new tissue where it doesn’t exist. It’s not exactly the same
process in place when we were in the womb, but we want to get to the same end
point to offer a better life for our wounded and for anyone suffering
traumatic nerve and bone injury.”
The pair has collaborated at Mayo
for five years on nerve and spinal cord regeneration and has successfully
regenerated peripheral nerves in the spinal cord of laboratory rats. They are
a couple of important regulatory steps away from testing their system on
humans in clinical trials.
Scaffolds
and Stem Cells
The system is comprised of
synthetic polymer scaffolds that deliver cells and nerve growth factors to
severed peripheral nerves. The goal is to recreate or regenerate the nerves
so patients’ functions and feelings will be restored. It entails several Mayo
Clinic innovations, including Dr. Yaszemski’s
development of the co-polymer, polycaprolactone fumarate, two compatible polymers never brought together
before, to serve as the scaffold. It involves novel efforts to use adult stem
cells from a patient’s own adipose (fat) tissues. And it brings to bear the
application of microfabrication techniques, such as
stereolithography — powerful lasers that form new
polymers, which are the foundation of the system’s architecture. The scaffold
is an analog of the naturally occurring extra cellular matrix, Dr. Yaszemski explains.
Two close up views of the synthetic
polymer scaffolds, with image (top) of myelinated
nerve fibers that have grown in the scaffolds.
“This is connective tissue that
provides the platform upon which cells, including stem cells, signaling
molecules and other components such as nerve growth factors ‘do their thing,’
if you will, that will stimulate nerves to regrow,”
he says. “To build new tissue, we need to provide that foundation which
functions to let cells that will make the natural tissue anchor to it.”
Peripheral nerves are sorts of electrical
connections between the brain and spinal cord that make muscles work and
feelings report from all over the body, Dr. Windebank
explains. The nerve is a very long cell; the cell body with its nucleus for
motor nerves that control muscle is in the spinal cord; if it’s a sensory
nerve, the cell body is beside the spinal cord. The very long extension of
the cell is called the axon. When severed, the part of the axon in continuity
with the cell body stays there, but the part beyond the cut — going into the
hand, for example — degenerates completely, along with the myelin, the
insulating material around it. To reestablish function, the nerve ending at
the cut has to regrow the entire length back to the
target in the hand.
The team is seeking approval from
the Food and Drug Administration and Mayo Clinic Institutional Review Board
for human clinical trials, which will involve defined injuries in which the
gap between the nerve cell body and the damaged axon is not so far to bridge.
“The goal of our research is to
come up with new strategies to build bridges in the peripheral nervous
system,” Dr. Windebank says. “The synthetic polymer
scaffolds are the basis of those bridges.”
Single lumen or tubule (A) and (B)
multiple lumen biodegradable nerve scaffolds. Frame C shows the flexibility
of a nerve guidance scaffold; it mimics the properties of a normal peripheral
nerve.
The researchers are creating an
environment whereby the synthetic polymer scaffolds support cells,
recognition and signaling molecules and nerve growth factors to generate new
nerve tissue over a period of weeks to months and then harmlessly biodegrades
in the body after delivering their goods.
Their system encourages a nerve to
grow so it gets longer and extends to its target. If this is done naturally,
a patient runs the risk of the nerve growing into a neuroma,
which Dr. Windebank describes as resembling a
knotted piece of wool, wrapped in circles, and very painful, one of the
reasons people endure much pain after amputations.
“There is a guidance component of
the system, with the scaffold providing the physical guidance and the growth
factors giving directional guidance,” Dr. Windebank
says. “There is a whole series of nerve growth factors well-known in their
developmental roles, and one of the things we’re doing is to supply these
factors to the regenerating nerves in a controlled way. We can essentially
impregnate the polymers with the nerve growth factors and then control how
they’re released.”
Scaffolds in regenerative medicine
also are made of minerals, primarily ceramics, and metals, mainly titanium
and tantalum. The Mayo researchers prefer synthetic polymers in this
application because they offer better control over the chemistry and
mechanical properties and flexibility compared with mineral or metal
counterparts.
“We can change polymer chemistry
if we feel that will be beneficial to do the job that we want done,” Dr. Yaszemski says. “For example, if we want a bone cell to
attach, there are certain sequences of peptides that those bone cells
recognize. We can modify the surface chemically and attach recognition
molecules. Bone cells would see this and recognize it as ‘home’.”
To create polycaprolactone
fumarate, polyester similar to the material in a
sports jacket, the researchers employed stereolithography,
an engineering technique used to make microchip computer components. It
allows the chemicals to operate in a watery environment and function as a
cross-linking polymer, rather than independent molecules, which is their
natural tendency. A pair of powerful lasers shone on the solution brings
about this polymerization.
The Yaszemski-Windebank
team has developed a method of procuring a patient’s own stem cells from
adipose tissue. It very recently received FDA approval.
“You make a small skin incision,
take out a small piece of fat, and we can make as many stem cells as we
need,” Dr. Windebank says.
Available also is a recent technique that allows them to take adult stem cells and engender them with the properties of embryonic stem cells. It was developed in other parts of the world and the country, but “it’s now in-house here,” he adds. (Editor’s note: see “iPS Cells (http://discoverysedge.mayo.edu/ips-regenerative-medicine/)
— Tony Fitzpatrick,
December 2009
Source: http://discoverysedge.mayo.edu/regenerative-medicine-military/index.cfm