Biomedical Engineering Reference
In-Depth Information
7.2.3 Composites of Silicate Bioceramics and Polymers
Ceramic/polymer composites have been considered third-generation ortho-
pedic biomaterials due to their ability to closely match properties (such as
surface, chemistry, biological, and mechanical) of natural bone. Mixing bio-
active ceramic powders with polymers is an effective method for generating
bioactivity to the polymer-matrix composites, but it is necessary to incorpo-
rate up to 40 vol% of bioactive ceramic powder. However, such a high mix-
ing ratio offsets the advantages of the flexibility and formability of polymer
matrix and it would be highly advantageous to lower the mixing ratio.
7.2.3.1 Particles
Liu and Webster (2010) demonstrated that well-dispersed ceramic nanopar-
ticles (titania or HAp) in PLGA improved mechanical properties compared
with agglomerated ceramic nanoparticles even though the weight percentage
of the ceramics was the same. Specifically, well-dispersed nanoceramics in
PLGA enhanced the tensile modulus, tensile strength at yield, ultimate ten-
sile strength, and compressive modulus compared with the more agglomer-
ated nanoceramics in PLGA (Liu and Webster 2010). Since surface loading of
ceramic powders in the polymer is thought to be an effective way of reducing
the mixing ratio of the ceramic powder while maintaining bioactive activ-
ity, CaSiO
3
/polylactic acid (PLA) composites were prepared by three meth-
ods: (1) casting, (2) spin coating, and (3) hot pressing. The bioactivity of these
samples was investigated
in vitro
using simulated body fluid. Apatite forma-
tion was not observed in the samples prepared by method 1 but some apa-
tite formation was achieved by mixing polyethylene glycol (PEG) with the
PLA, producing a porous polymer matrix. In method 2, apatite was clearly
observed after soaking for 7 days. Enhanced apatite formation was observed
in method 3, the thickness of the resulting apatite layers is about 20 microm
after soaking for 14 days. Since the amount of CaSiO
3
powders used in these
samples was only ≤0.4 vol%, it is concluded that this preparation method
is very effective in generating bioactivity in polymer-matrix composites by
loading with only very small amounts of silicate ceramic powder (Okada et
al. 2007).
7.2.3.2 Microspheres
CaSiO 3 (CS) has been proposed as a new class of material suitable for bone
tissue repair due to its excellent bioactivity. Wu, Zhang, Fan, et al. (2011) incor-
porated CS into PLGA microspheres to investigate how the phase structure
(amorphous and crystal) of CS influences the
in vitro
and
in vivo
bioactivity
of the composite microspheres. The results showed that the incorporation
of both amorphous-CS and crystal-CS enhanced the
in vitro
and
in vivo
bio-
activity of PLGA microspheres. Crystal-CS/PLGA microspheres improved
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