Biomedical Engineering Reference
In-Depth Information
purposes must be able to withstand the physio-
logical stressors present
in situ,
allow cells to
infiltrate the scaffold, and permit the exchange
of nutrients and waste. The cells are comparable
to workers, and the vasculature and extracellular
matrix represent material stores enabling the
cells to grow, proliferate, and produce tissue.
Finally, as constructional scaffolds must be
removed, biological skeletal aids must be
resorbed by the body, leaving the newly formed
tissue intact and functional
[1, 2]
.
The advent of engineered scaffolding systems
for medical use was prompted by the desire of
surgeon J. P. Vacanti to address the critical short-
age of organ donors in the 1980s and 1990s.
Regenerative strategies employing tailored scaf-
folds conceivably would remedy issues with
grafts (
autologous
—from the same organism,
allogeneic
—from the same species,
xenogeneic
—
from a different species). Although researchers
have made significant gains in refining tissue
engineering scaffolding, very few have been
clinically implemented
[3]
. Consequently, sub-
optimal treatments as gold standards of care still
persist.
multiple surgeries involved with this procedure
often lead to higher healthcare costs, prolonged
recovery times, and an increased susceptibility
to pathogens. To overcome these challenges, the
development of tissue-engineered scaffolds is
a primary objective for several researchers and
medical practitioners around the globe.
Improved treatments are also needed for
anterior cruciate ligament (ACL) ruptures or
tears. The ACL, one of four ligaments that aids
in stabilizing the knee, functions to support and
strengthen the knee while preventing excessive
anterior motion
[6, 7]
. As a result of its posi-
tion, there is a relatively high incidence of ACL
injuries, with an estimated 200,000 patients per
annum being diagnosed with disrupted ACLs.
The relatively high frequency of these ligament
injuries is a direct result of athletes participating
in high-risk sports such as basketball, football,
and soccer. Although the current standard of
care for ACL reconstruction—the use of auto-
grafts—is often successful, there are still signifi-
cant drawbacks to the procedure. The autograft
tissue is typically taken from the patellar ten-
don, hamstring tendon, or quadriceps tendon.
These tendons have limited availability and
require multiple surgical procedures. Moreover,
if allografts are employed, there is an increased
likelihood of infection and transplant rejection
[3]
.
Another prominent area of medicine in
which inadequate care exists is in the treatment
of coronary artery disease (CAD). It is esti-
mated that CAD accounts for approximately
50% of the nearly 1 million deaths resulting
from cardiovascular disease every year
[8]
.
CAD involves the narrowing of arteries as a
result of plaque, cholesterol, lipids, and other
materials accumulating on the interior of arte-
rial walls. As the luminal space progressively
narrows, oxygen is effectively prevented from
reaching the heart. When the severity of the
blockage renders angioplasty ineffective, grafts
are often used to circumnavigate the occluded
7.1.1 Limitations of Current Practices in
Tissue Regeneration
More than 3 million musculoskeletal procedures
are done annually in the United States; about
half of these involve bone grafting with either
an autograft or an allograft
[4]
. An autograft is
tissue taken from a person and implanted else-
where in his body, whereas an allograft involves
tissue borrowed from another person. As the
gold standard of care for bone injuries, autografts
account for the majority of the 500,000 bone-
grafting procedures performed annually in the
United States and the more than 2.2 million per-
formed worldwide
[5]
. Bone autografts are ideal
in their capacity to support new bone growth;
however, grafts often lead to donor-site morbid-
ity and are limited in supply
[5]
. Moreover, the
