Biomedical Engineering Reference
In-Depth Information
4.
Biodegradable Orthopedic Implants
Hansoo Park, Johnna S. Temenoff, and Antonios G. Mikos
List of Abbreviations
current treatments using nondegradable fi xa-
tion materials have proven effi cacious, tissue-
engineering approaches with biodegradable
implants are being considered as promising
future alternatives [
ECM: extracellular matrix
GAG: glycosaminoglycan
HA: hyaluronic acid
MMP: matrix metalloproteinase
OPF: oligo(poly(ethylene glycol) fumarate)
PBS: phosphate-buffered saline
PCL: poly(
]. One possible advan-
tage of these systems is that biodegradable
implants can be engineered to provide tempo-
rary support for bone fractures, and because
they can degrade at a rate matching new tissue
formation, their use can eliminate the need for
a second surgery [
8
,
49
-caprolactone)
PEG: poly(ethylene glycol)
PEG-DA: poly(ethlylene glycol)-diacrylate
PEG-DM: poly(ethlylene glycol)-
dimethacrylate
PGA: poly(glycolic acid)
PLA: poly(lactic acid)
PLGA: poly(lactic-co-glycolic acid)
POE: poly(orthoester)
PPF: poly(propylene fumarate)
PPF-DA: poly(propylene fumarate)-diacrylate
rhBMP-
ε
]. In addition to providing
support for the tissue surrounding a defect,
the scaffold can serve as a substrate for seeded
cells, facilitating new tissue formation at the
site of injury [
49
]. The incorporation of
drugs or bioactive molecules may also acceler-
ate new tissue formation, or can be used to
treat specifi c conditions, such as osteomyelitis
[
35
,
100
].
In designing biodegradable orthopedic
implants, several important factors should be
considered. First, the material should degrade
over an appropriate time, so that the scaffold
functions as a temporary support, but allows
space for newly generated tissue to replace the
defect [
4
,
10
: recombinant human bone
morphogenetic protein
2
2
TGF-
β
1
: transforming growth factor
β
1
4.1 Introduction
]. Second, neither the initially
implanted biomaterials nor the degraded mate-
rials and related products, such as monomers,
initiators, and residual solvents, should elicit a
serious infl ammatory or immunogenic response
in the body [
49
,
91
Over the past
years, there have been signifi -
cant advances in the development of biode-
gradable materials [
30
]. In particular, these
materials have received attention for use as
implants to aid regeneration of orthopedic
defects [
79
]. Finally, the material should
possess suffi cient mechanical strength to
sustain loads applied to defects during the
healing process. Additionally, the material
should show a decrease in mechanical strength
as defects are replaced with new tissue to
28
1
million orthopedic surgeries are performed in
the United States alone [
49
,
91
]. Every year more than
3
.
1
]. However, although
55
