Biomedical Engineering Reference
In-Depth Information
60
processes (autoclave, ethylene oxide and
Co irradiation) may affect
the polymer properties [122].
There is a variety of biocompatible polymers suitable for
biomedical applications [123, 124]. For example, polyacrylates,
poly(acrylonitrile-
-vinylchloride) and polylysine have been
investigated for cell encapsulation and immunoisolation [125, 126].
Polyorthoesters and PCL have been investigated as drug delivery
devices, the latter for long-term sustained release because of their
slow degradation rates [127]. PCL is a hydrolytic polyester having
appropriate resorption period and releases nontoxic byproducts
upon degradation [128]. Other polyesters and PTFE are used for
vascular tissue replacement. Polyurethanes are in use as coatings
for pacemaker lead insulation and have been investigated for
reconstruction of the meniscus [129, 130]. Polymers considered for
orthopedic purposes include polyanhydrides, which have also been
investigated as delivery devices (due to their rapid and well-defined
surface erosion), for bone augmentation or replacement since they
can be photopolymerized
co
[127, 131, 132]. To overcome
their poor mechanical properties, they have been co-polymerized
with imides or formulated to be cross-linkable
in situ
[132]. Other
polymers, such as polyphosphazenes, can have their properties (e.g.,
degradation rate) easily modified by varying the nature of their side
groups and have been shown to support osteoblast adhesion, which
makes them candidate materials for skeletal tissue regeneration
[132]. PPF has emerged as a good bone replacement material,
exhibiting good mechanical properties (comparable to trabecular
bone), possessing the capability to cross-link
in situ
through the C=C
bond and being hydrolytically degradable. It has also been examined
as a material for drug delivery devices [127, 131-134]. Polycarbonates
have been suggested as suitable materials to make scaffolds for bone
replacement and have been modified with tyrosine-derived amino
acids to render them biodegradable [127]. Polydioxanone has been
also tested for biomedical applications [135]. PMMA is widely used
in orthopedics, as a bone cement for implant fixation, as well as to
repair certain fractures and bone defects, for example, osteoporotic
vertebral bodies [136, 137]. However, PMMA sets by a polymerization
of toxic monomers, which also evolves significant amounts of heat
that damages tissues. Moreover, it is neither degradable nor bioactive,
does not bond chemically to bones, and might generate particulate
debris leading to an inflammatory foreign body response [131, 138].
in vivo
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