Bioactive Polymers and Nanobiomaterials Composites for Bone Tissue Engineering - Biomimetics: Advancing Nanobiomaterials and Tissue Engineering - page 97

(HDPE) was reinforced with either the synthesized HAp whiskers or a
commercially available spherical HAp powder using a novel powder
processing technique that facilitated uniform dispersion of the additive
in the matrix prior to compression molding. An increase of the volume
fraction of either of the two reinforcement types by more than 0-50 vol%
resulted in increased elastic modulus, a maximum in ultimate tensile stress
and decreased work-to-failure rate. Due to alignment of the whiskers in
the matrix during processing, composites containing HAp whiskers were
anisotropic and had higher elastic modulus, maximum tensile strength and
work-to-failure rate relative to composites reinforced with spherical HAp.
Other researchers [32] studied the effect of partially stabilized zirco-
nia (PSZ) on the biological properties of the HDPE/HAp composites by
investigating the simultaneous effect of HAp and PSZ volume fractions on
the in vitro response of human osteoblast cells. It was found that the vol-
ume fraction of HAp has a signifi cant effect on the bioactivity of the com-
posites. The composites provided a favorable site for cell attachment, with
cells frequently found to be anchoring to the HAp particles. Interestingly,
the results show that the addition of PSZ into the HDPE/HAp compos-
ites does not adversely affect the biological properties of these composites
and, in some cases, composites with PSZ showed better biological results
than HDPE/HAp systems [32].
Tricalcium phosphate [TCP; Ca 3 (PO4) 2 ] is another class of ceramic-
based effective candidate material for bone tissue engineering, which
showed excellent osteoconductivity and bioactivity [33-35]. Although
there are several types of TCP such as, b -TCP, a - TCP, a ' TCP, and g -TCP
[36], only b -TCP is widely used for bone tissue engineering due to its
simple and defi ned fabrication process. It has been reported [37-39] in
several studies that nanoparticle b -TCP composites could enhance the cel-
lular proliferation and bioactivity of osteoblast cells. However, the lack of
tensile strength of b -TCP alone limited the application of this biomaterial
in load-bearing clinical applications [40]. Therefore, the combination of
low grain-sized b -TCP particles with fl exible polymer matrices, e.g., poly-
ethylene (PE), could improve its mechanical properties for a wide range
of applications such as artifi cial hip joints. Homaeigohar and coworkers
[41] investigated the skeletal cell lines proliferation using b -TCP/HDPE
blends as matrix and confi rmed signifi cant improvement. Therefore,
b -TCP nanoparticles blended with HDPE or UHMWPE as scaffolds can
be used for bone tissue remodeling of effective matrices (Table 5.1) [42].
5.3.2 PolyamidesNanocomposites
Polyamides (PAs) are semicrystalline engineering polymers with a wide
range of suitable properties. There are a number of different PAs, but
PA-6,6 has good mechanical properties, exhibits good biocompatibility