Biomedical Engineering Reference
In-Depth Information
osteoconductivity, biocompatibility, and high stiffness retainable for
the period necessary to achieve bone union [388]. The initial bending
strength of ~280 MPa exceeded that of cortical bone (120-210
MPa), while the modulus was as high as 12 GPa [168]. The strength
could be maintained above 200 MPa up to 25 weeks in phosphate-
buffered saline solution. Such biocomposites were obtained from
precipitation of a PLLA/dichloromethane solution, where small
granules of uniformly distributed CDHA microparticles (average
size of 3 µm) could be prepared [167]. Porous scaffolds of PDLLA
and HA have been manufactured as well [332, 397, 398]. Upon
implantation into rabbit femora, a newly formed bone was observed
and biodegradation was significantly enhanced if compared to
single-phase HA bioceramics. This might be due to a local release of
lactic acid, which in turn dissolves HA. In other studies, PLA and PGA
fibers were combined with porous HA scaffolds. Such reinforcement
did not hinder bone ingrowth into the implants, which supported
further development of such biocomposites as bone graft substitutes
[50, 51, 377, 399, 400].
Blends (named as SEVA-C) of EVOH with starch filled with 10-30
wt.% HA have been fabricated to yield biocomposites with modulus
up to ~7 GPa with a 30% HA loading [401-406]. The incorporation
of bioactive fillers such as HA into SEVA-C aimed to assure the
bioactive behavior of the composite and to provide the necessary
stiffness within the typical range of human cortical bone properties.
These biocomposites exhibited a strong
bioactivity that was
supported by the polymer's water-uptake capability [407]. However,
the reinforcement of SEVA-C by HA particles was found to affect the
rheological behavior of the blend. A degradation model of these
biocomposites has been developed [408].
Higher homologues poly(3-hydroxybutyrate), 3-PHB, and
poly(3-hydroxyvalerate), 3-PHV, show almost no biodegradation.
Nevertheless, biocomposites of these polymers with calcium
orthophosphates showed a good biocompatibility both
in vitro
in vitro
and
in vivo
[102, 409-415]. Both bioactivity and mechanical properties
of these biocomposites can be tailored by varying the volume
percentage of calcium orthophosphates. Similarly, biocomposites
of PHBHV with both HA and amorphous carbonated apatite
(almost ACP) appeared to have a promising potential for repair and
replacement of damaged bones [416-419].
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