Biomedical Engineering Reference
In-Depth Information
PMMA/HAp composites. An increase in biological activity of bone cements
in response to increasing HAp content was observed. The authors suggested
that loading of HAp into cements could be the way forward in producing
active materials with the the biological properties that benefi t the patient.
Kwon and coworkers conducted studies [61] that showed that a PMMA/
HAp composite (30 wt% of HAp) increased the interfacial shear strength
at the bone-implant interface 6 weeks after implantation in rabbits. Several
other studies also found that the addition of HAp can enhance the mechani-
cal properties of bone cements, although the extent of improvement varied,
depending on the type of bone cement [62]. The response of osteoblasts to
PMMA/HAp materials was also investigated by Moursi
et al.
[63], and found
that osteoblasts proliferation was improved when PMMA/HAp was used
when compared to those of traditional materials (titanium and PMMA).
The PMMA-based nanocomposites with various forms of TCP were
also investigated by several other research groups [64-68]. The prepara-
tion of PMMA-based composites were enriched with
b
-TCP and BaSO
4
to
improve the inherent porosity of cement, thus increasing the amount of
absorbed antibiotic. These properties and their
in vitro
and
in vivo
perfor-
mance have also been studied [64, 65]. Yasuda
et al.
[67] reported the
a
-TCP
dissolved in the body faster than both HAp and
b
-TCP. Thus, the biocom-
patibility of HAp/
a
-TCP and HAp/
b
-TCP composites is expected to be
different from each other. Authors demonstrated the method of prepara-
tion of dense HAp/
a
-TCP composites by a colloidal process. The colloidal
process suppresses agglomeration due to electrostatic, steric or electro-
static repulsive force by polymer dispersant. An addition of the appropri-
ate amount of dispersant leads to a good dispersion of particles, resulting
in better mechanical properties. The composite of HAp/
a
-TCP was dis-
persed in PMMA matrix and was found to form porous structure contain-
ing 100 μm-sized pores to incorporate cells needed for bone regeneration
and to allow bone ingrowth. The biological properties of PMMA/
a
-TCP
composite was tested by means of
in vitro
and
in vivo
investigations and
the results were compared with those for controlled PMMA. Osteoblast
cultures (MG63) demonstrated that composites signifi cantly improved
osteoblast viability [68], and the implant of PMMA/
a
-TCP composite suc-
cessfully osteointegrated in trabecular and cortical tissue within 12 weeks.
Recently, other types of nanomaterials, namely carbon nanotubes [69] and
wollastonites [70], have been incorporated into the PMMA matrix, and
their physical and mechanical properties have been investigated [69].
5.4
Biodegradable Polymer and Nanocomposites
Over the last two decades there has been an increasing demand for
biodegradable and bioresobable materials for tissue engineering and
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