CELL - BASED NANOCOMPOSITES AND BIOMOLECULES FOR BONE TISSUE ENGINEERING - Advanced Biomaterials: Fundamentals, Processing, and Applications - page 542

as these materials do not get resorb in the body. Yet, the risk of implant failure is
prevalent and remnants of the failed implant will elicit an infl ammatory response,
hampering bone repair. This calls for a new generation of materials for bone
applications, particularly tissue-engineered bone grafts, which will be dealt with in
this chapter.
16.2 BONE GRAFTS
16.2.1 Current Bone Grafts and Bone Graft Substitutes
The gold standard for bone grafts is autologous bone grafts, also known as auto-
grafts, whereby healthy bone tissue is harvested from the patient and implanted
in the diseased site. One of the major advantages of autografts is that there is no
immunological response due to host compatibility and the presence of osteopro-
genitor cells and bone morphogenetic proteins (BMPs) needed for bone regen-
eration. The main drawbacks are donor site immobility and risk of infection at the
site of harvest. Allografts are grafts that are derived from another donor of the
same species, often from cadavers that are freeze-dried. Some benefi ts of allografts
include eliminating donor site morbidity caused by bone harvesting from the
patient and a second operative procedure. One of the disadvantages of allografts
is the possible immunological response in the patient as allografts are harvested
from another donor. As such, there is a risk of disease transmission. Furthermore,
donor shortage may also be an issue.
To circumvent some of the defi ciencies associated with autografts and
allografts, scientists have come up with bone graft substitutes, which consist of
systems based on deminerialised bone matrix (DBM), bioceramics, BMPs, coral
and composites. DBM is a processed product of allograft containing growth
factors, collagen and proteins and it comes in various forms such as putty, inject-
able gel, granules or powder. Since DBM is further processed, the risk of disease
transmission is reduced but it does not provide a strong framework for bone
healing. Although bioceramics such as tricalcium phosphate (TCP) and hydroxy-
apatite (HA) do not carry the risk of disease transmission, due to the lack of
bioactive molecules, bone regeneration may be impeded or the repair may occur
at a slower rate.
Some researchers had attempted to combine autogenous bone grafts and
DBM to treat tibial and femoral non-unions 4 - 6 . Out of thirty femoral non-
unions cases, twenty-four were healed within six months after surgical interven-
tion. Four patients needed a second plate before healing took place and the
remaining two cases were lost to follow-up. Others have shown that demineral-
ized bone matrix gel could be used as a supplement material to compensate
for the lack of autograft volume without compromising the fusion rates as of
those who used autografts alone 7 . Different manufacturers have their own pro-
curement, demineralization, and sterilization procedures. Individual DBMs
are often coupled with different carrier materials such as calcium sulfate,