Biomedical Engineering Reference
In-Depth Information
potential is unclear.
126
animal studies have demonstrated that iGF may be
administered systemically to increase bone formation. iGF-i effects were
age-dependent, being absent in young, rapidly growing animals.
130
in a
rat tibia model, the local administration of iGF-i had a greater stimulating
effect on fracture healing than tGF-b; the application of both GF resulted
in a significantly higher maximum load and torsional stiffness.
131
Although recombinant GF may be used for specific clinical applications,
there is concern that a single dose of exogenous protein will not induce an
adequate biological response in patients, particularly in situations in which
the viability of the host bone and surrounding soft tissues is compromised.
a better strategy for protein delivery might be gene therapy, which involves
the transfer of genetic information to cells. there are two ways to deliver
the required GF gene to the regeneration site: it can be delivered directly to
the tissue so that host cells are transfected and express the protein (
in vivo
transduction) or the gene can be delivered through transfection of cultured
cells, which are implanted at the regeneration site (
in vitro
transduction). in
general, the duration of protein synthesis after gene therapy depends on the
technique used to deliver the gene to the cell. Both short-term and long-term
expression are possible. the treatment of the bone repair defects usually
requires short-term protein production, while long-term expression is useful in
chronic diseases such as osteoporosis. MSC, genetically engineered to express
BMp-2,
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have been shown to stimulate osteogenesis and angiogenesis. Before
the clinical application of the gene therapy, however, questions concerning
the safety of viral vectors and the immunological reactions to viral proteins
need to be addressed.
autologous or homologous platelet rich plasma (prp) is used to accelerate
bone repair through the osteogenic GF released from platelet a-granules
during activation.
133
the advantages of prp lie in its mimicking the GF
effects of the physiological wound healing and regenerative tissue processes.
Moreover, if autologous prp is used, immunological reactions are avoided.
the drawbacks consist in the unpredictability of GF concentrations in different
preparations, owing both to individual factors and to different preparation
methods. The efficiency of PRP in improving bone regeneration is increased
by its combination with bone allografts.
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a recent prospective, randomized,
controlled clinical study has demonstrated that prp alone or combined with
bone marrow stromal cells increases the osteogenetic potential of lyophilized
bone chips.
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3.5.7 Demineralized bone matrix
dBM is the product of acid extraction of allograft bone, resulting in the
loss of most of the mineralized component. it contains type i collagen,
non-collagenous proteins and osteoinductive GF (BMp, GdF, tGF-b1, -2
