When
good materials go bad
Julia Shuck, posted Nov. 17, 2006
As the movie clip begins, an Australian man is bungee jumping
toward a river with full intentions of bouncing right back.
Before he is jerked back into the air, a hidden alligator
caught him, letting nothing but a bungee cord jerk into the
air. This was Sheila Grant’s, MU assistant professor
of biological engineering, way of showing the audience what
it’s like when you expect one thing, such as a successful
implant, but something backfires, such as the body rejecting
the implant of a biomaterial.
Grant’s topic, “Biomaterials: When Good Materials
Go Bad,” discussed biocompatibility, biomaterials and
their implants. Hip and knee replacements, weak arteries and
hernias were the key topics of Nov. 11’s Saturday Morning
Science. The program is almost over for the year with only
two more sessions remaining in the weekends to follow Thanksgiving
break.
According
to Grant, a biomaterial is a “nonviable material used
in a medical device intended to interact with biological systems,”
such as knee and spine replacements and wall support in the
stomach, heart and veins, to name a few.
Different materials are used for different implant parts and
uses in the body. The preferred material for hip replacements
is ceramics, such as alumina and zircomia, which have less
friction that our natural hips, according to Grant. Silicone,
Poly Propaline and Polyurethane, to name a few polymers, are
used to repair hernias and removable stitches. This mesh-looking
material, which has some give, allowing for the body to easily
move around, can be implanted in the case of a hernia.
“Hernias are a breakdown of the tough connective tissues
that encases the abdominal musculature,” Grant said.
Stints, which resemble thin-zigzagged wire, are also made
from polymers and are used to support weakened arteries.
A few factors that can lead to an unsuccessful implant include
corrosion due to poor manufacturing, packaging or handling;
a lot of movement in the body that can wear the piece down;
the corrosion of metals which is highly toxic; and using a
one-size-fits-all piece instead of one that is customized.
Another possible side effect of getting an implant is Osteoporosis,
which is the breaking down of our bone because materials are
so much more stronger than out bones and they implants corrode,
according to Grant. Hernia implants in the abdomen can lead
to a painful growth between the mesh implant and the organs.
In 1999, the average age of someone getting a knee replacement
was 87, in 2003 the average age lowered to 67. In 2003, 418,000
people received knee replacements. Knee replacements are meant
to last 10 to 15 years, which isn’t that big of a deal
for an 85-year-old, but can be detrimental to someone that
is 65 years of age.
There are three main results from a body when it rejects foreign
materials. The body can ingest the implant using white blood
cells, wall it off by just pretending it is not there and
working around it or the implant can be expelled.
An example Grant gave was one patient who had a hernia replacement
and his body rejected it. The disk that was implanted forced
its way out of his body through his back and was easily extracted
by his doctor who just had to pull on the metal piece. “The
doctor said that in 20 years he had never seen anyone reject
the pin,” said Betty Crigler who received an implant
in her foot after having surgery on her bunions. “It
didn’t hurt at all,” said Crigler referring to
the pin that was being pushed out of her foot by her body.
