THE NOVEL APPROACH involves using cloned genes and smart grafts to
foster bone regrowth in the area of injury, said Cato Laurencin of
Allegheny University Hospitals in Philadelphia.
Known as tissue engineering, the technique was made possible by the
cloning of genes that produce a natural growth factor that allows bone
cells to sprout where only dead tissue had been before.
So far, the new strategy is working, growing new bone in injured
rats and rabbits within a matter of weeks, Laurencin told a scientific
meeting in Philadelphia. Human testing is expected within five years.
The technique makes the current methods of transplanting bone tissue
from either a cadaver or from another part of the body seem barbaric, he said.
And within a decade or two, he said, similar methods will be used to
repair muscle, heart and other injured tissues. “As we move into the next
millennium, tissue engineering is going to revolutionize the repair,
restoration and regeneration of all types of body tissues.”
STIMULATING BONE GROWTH
The simplicity of the system is particularly noteworthy. A disciple
of what he calls the Volkswagen approach, Laurencin said, “You don’t need a
very complex system to stimulate blood vessels and bone growth. What we
need is a graft for all the people.”
The scenario, he said, would be something like this: First, some of
the patient’s healthy cells are removed by a simple needle biopsy. Then,
the cells and the cloned growth factor genes are implanted together into a
graft whose appearance he likened to a crouton.
As the cells begin to divide, the cloned genes begin producing the
growth factor protein needed for healing. Each time the cells divide, more
growth factor is produced; the process is allowed to continue for several
days before the entire complex is transplanted into the area of injury.
Once transplanted, the grafts, grown on a scaffold composed of smart
materials that biodegrade in the body in a matter of weeks, continue to
release the growth factor, sprouting blood vessels at the injured site. The
blood vessels, in turn, provide nourishment to the stem cells that are
constantly being produced by our bone marrow, Laurencin said, and bone
cells proliferate.
A patient’s graft is made from any of three compounds of varying
strengths that form a continuum from materials like those of the newer
sutures that dissolve in the body in a few days to smarter compounds
similar to the Kevlar used in bullet-proof vests.
A person with a simple finger fracture, for example, needs a less
durable graft that would dissolve in the body within six weeks, Laurencin
said, while a broken hip would require a graft that would last six months
or more.
LESS PAIN, LESS RISK
The method is not only associated with less pain and fewer
complications than methods now used to treat bone loss, he said, but solves
the problem of supply that now limits them.
Currently, a person with a crushing arm bone injury, for example,
has two choices: painful surgery in which a bone graft is taken from the
hip or a graft from a cadaver. The former often leaves the patient with an
agonizing limp, he said, while the latter can transmit viral diseases. Both
are in limited supply.
All these problems are obviated through tissue engineering,
Laurencin said.
But even more exciting, said fellow engineer Thomas Budinger, is the
possibility of using bioengineering to regenerate heart tissue.
Even if not stricken by a disease such as cancer or a heart attack,
a person eventually dies due to old age — his heart tissue simply becomes
too old to function, said Budinger, of the Lawrence Berkeley National
Laboratory in Berkeley, Calif.
But if heart tissue can be rejuvenated, he said, the healthy elderly
could expect to add decades to their lives.