Biomedical Engineering Reference
In-Depth Information
the amount of glutaraldehyde cross-linking agent should be less
than 8% to decrease the toxicity on the osteoblasts and to avoid
inhibition of cellular growth caused by the release of residual or
uncross-linked glutaraldehyde. A long-term implantation study of
PDLLA/α-TCP composites in a loaded sheep implant model showed
good results after 12 months but a strong osteolytic reaction after
24 months. This was ascribed to the almost complete dissolution of
α-TCP to this time and an adverse reaction of the remaining PDLLA
[488].
More complex calcium orthophosphate-based formulations are
known as well. For example, there is a biocomposite consisting of
three interpenetrating networks: TCP, CDHA and PLGA [489]. Firstly,
a porous TCP network was produced by coating a polyurethane foam
by hydrolysable α-TCP slurry. Then, a CDHA network was derived
from a calcium orthophosphate cement filled in the porous TCP
network. Finally, the remaining open pore network in the CDHA/
α-TCP structures was infiltrated with PLGA. This biocomposite
consists of three phases with different degradation behavior. It was
postulated that bone would grow on the fastest degrading network
of PLGA, while the remaining calcium orthophosphate phases would
remain intact thus maintaining their geometry and load bearing
capability [489].
6.4.1.3 Other calcium orthophosphate-based biocomposites
The number of research publications devoted to biocomposites
based on other calcium orthophosphates is substantially lesser than
those devoted to apatites and TCP. BCP, which is a solid composite
of HA and β-TCP; however, similar composites of HA and α-TCP are
possible, as well (see section
for details) appears to be most
popular among the remaining calcium orthophosphates. For example,
collagen-coated BCP ceramics was studied and the biocompatibility
towards osteoblasts was found to increase upon coating with
collagen [490]. Another research group created porous PDLLA/
BCP scaffolds and coated them with a hydrophilic PEG/vancomycin
composite for both drug delivery purposes and surface modification
[491]. More to the point, both PLGA/BCP [492, 493] and PLLA/BCP
[494] biocomposites were fabricated and their cytotoxicity and
fibroblast properties were found to be acceptable for natural bone
tissue reparation, filling and augmentation [495, 496]. Besides, PCL/
1.3.14
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