Bioactive Polymers and Nanobiomaterials Composites for Bone Tissue Engineering - Biomimetics: Advancing Nanobiomaterials and Tissue Engineering - page 105

HAp-containing bioactive composites are suitable as bone-fi lling mate-
rials without any side effects, which has been demonstrated by implanta-
tion in an animal model in vivo for bone tissue regeneration (Figure 5.3)
[75, 76]. The complete process of bioresorption and concurrent bone
replacement of rods made of forged composites of PLLA and raw HAp
particles implanted in the femoral medullar cavities of rabbits has been
described [77]. The results of this procedure in terms of bioresorption,
osteoconductive bioactivity and bone replacement in three implantation
sites were compared (Figure 5.3).
Recently, researchers have demonstrated [78, 82] that PLLA can be
functionalized by chemical grafting onto the hydroxyl groups in the sur-
face of nanoHAp particles by ring-opening polymerization. These PLLA-
grafted HAp materials had better mechanical and bending strength with
improved cellular compatibility [82] which are required for bone tissue
regeneration as compare to that of non-grafted composites. The compos-
ites of poly(D,L-lactide) (PDLLA) and HAp have been developed which
possess biodegradation, biocompatibility and shape memory properties
[83]. Such shape memory effect may have a certain advantage for some
bone implant applications to mimic the exact shape of the bone. Other
researchers [85] have reported that titanium dioxide (TiO 2 ) nanoparticles
can be used as a promising fi ller material for use in designing bone tissue
engineered constructs based on PLA matrices.
5.4.1.2 Poly(e-caprolactone) (PCL) Nanocomposites
PCL is a linear polyester and a semicrystalline polymer with a degree of
crystallinity (50%) and a glass transition temperature of about −60°C and
melting temperature of about 65°C. Currently, PCL is regarded as a can-
didate polymer for tissue engineering, as it shows suitable mechanical
properties to serve as a scaffold in applications where a highly resilient
material is required, e.g., bone substitution, where the physical proper-
ties of the scaffold have to be maintained for at least 6 months [86]. The
PCL/HAp composite scaffolds fabricated using PCL as matrix and HAp
nanoparticles as a fi ller material, prepared by phase inversion and solu-
tion casting techniques, have been found to give [86] better mechanical
strength and osteoblast growth (in comparison to pure PCL). The topic
has been the subject for a spate of research activities by many research
groups around the world [87, 88]. Some authors have reported [87] that
the mechanical properties of the composites, particularly the values of
elastic modulus, is within the same range of that for human cortical bone,
following addition of 20% HAp into the polymer matrix. Furthermore,
PCL/HAp scaffolds have been used for in vitro cell culture studies using
primary human osteoblasts. Observation of a high proliferation rate and
a moderate increase of alkaline phosphatase activity indicated osteogenic