Biomedical Engineering Reference
In-Depth Information
HAp particulates have been incorporated into PEEK matrix using a vari-
ety of processing techniques, i.e., melt compounding, granulating and
injection molding [48]. Authors have demonstrated the feasibility of
fabricating PEEK/HAp biocomposites with high HAp loading of up to
40 vol% [49], which was achieved through appropriate selection of the
processing parameters.
Tricalcium phosphate has been used to prepare PEEK/TCP compos-
ites using a variety of methods, for example, compounding and injection
molding [50] and selective laser sintering (SLS) [51-53]. The latter method
can also be used to produce macroporous scaffolds with a network struc-
ture similar to that of bones.
Cell attachment on bioactive PEEK composites has been demonstrated
using fi broblasts [54], human osteoblasts [43, 50], and human fetal osteo-
blasts [53]. Osteoblast proliferation and spreading were reported to be
greatest for bioglass (45S5)-reinforced PEEK, followed by PEEK and then
b -TCP-reinforced PEEK [50, 51, 53]. However, another study reported no
differences in osteoblast proliferation and alkaline phosphatase activity
(differentiation) for PEEK, HA-reinforced PEEK, and Sr-HA-reinforced
PEEK [55]. HA alone is known to suppress cell proliferation but enhance
differentiation [56]. Systematic investigations for the effects of the bioac-
tive reinforcement composition, content, size, and morphology on cellular
behavior are needed in the future. Recently, research results on carbon
nanotubes (CNTs)/PEEK composites have been reported [57, 58]. The
authors undertook studies on their physical and mechanical properties.
However, it was indicated that further studies on CNT-based PEEK com-
posites need to be conducted to understand cellular behavior and the
mechanism of bone tissue formation.
5.3.4
Poly(methyl methacrylate) (PMMA) Nanocomposites
PMMA and its derivatives are the polymers most commonly used as bone
cements for fi xation in orthopaedic surgeries. PMMA is an amorphous ther-
moplastic polymer and is still the current standard for cement-held prostheses.
It is an inert material for fi broblastic cells observed at the bone-cement
interface. It forms a strong bond with the implant, but the bond between
the cement and the bone is considered to be weak, with fi broblastic cells
observed at the implant site. Incorporation of HAp increases the bio-
logical response to the cement from tissue around the implant site, thus
giving increased bone apposition. Research revealed that the addition of up
to 40 wt% of HAp to PMMA cement has been shown to increase the fracture
toughness, and that the addition of up to 15 wt% of HAp led to an increase
in fl exural modulus, while the tensile and compressive strengths remained
unchanged [59]. Dalby and coworkers [60] used an in vitro tissue culture
model to evaluate the biological response of conventional PMMA and
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