Biomedical Engineering Reference
In-Depth Information
12.3.6
Bone Tissue Grafts
Bone tissue occurs in different bones of the skeleton. Bone is a
hard and rigid tissue. Like cartilage, bone consists of living cells
with large amounts of ground substance or matrix. It is impreg-
nated with organic salts, such as calcium carbonate (7%) and cal-
cium phosphate (85%). Small amounts of sodium and magnesium
are also present. In addition to this, the matrix contains numer-
ous collagenous fibers and a large amount of water. Collagen fibers,
together with bone cells, constitute the organic (living) matter in
bonetissue.Boneservesseveralcriticalfunctions,includingprovid-
ing muscular support, producing blood cells and immune cells, and
acting as a mineral reservoir to maintain electrolyte balance in the
body. Bone may be lost after trauma, cancer, fractures, periodonti-
tis, osteoporosis, and infectious disease, and presently there is no
definitive method for regeneration.
32
Bone grafts are increasingly
used; however, they are plagued by high failure rates of between
16% and 50%.
33
Autografts also present problems associated with
a secondary surgery site, as well as a limited supply and morbid-
ity of the donor site.
34
Similarly, metal implants have a high failure
rate and often require a second surgical procedure.
35
The design of
scaffolds for bone tissue engineering (BTE) is based on the phys-
ical properties of bone tissue, such as mechanical strength, pore
size, porosity, hardness, and overall 3D architecture. For BTE, scaf-
folds with a pore size in the range of 100-350
μ
mandporos-
ity greater than 90% are preferred for better cell/tissue ingrowth
and hence enhanced bone regeneration.
36
To overcome the draw-
backs of the current bone graft materials, BTE using bone marrow
stem cells has been suggested as a promising technique for recon-
structing bone defects. To understand the influence of mesenchy-
mal stem cells (MSCs) on nanofibers, MSCs derived from the bone
marrowofneonatalratswereseededonananofibrousscaffold.The
resultsindicatedthattheMSCsmigratedinsidethescaffoldandpro-
ducedanabundantECMinthescaffold.Incontinuationtothisstudy,
Shin
et al.
tested PCL nanofibers, along with MSCs
in vivo
in a rat
model. Their results demonstrated ECM formation throughout the
scaffold, along with mineralization and type I collagen synthesis.
37
These studies demonstrated that PCL-based nanofibrous scaffolds
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