Biomedical Engineering Reference
In-Depth Information
which can form at lower sintering temperatures of 700°C (Langstaff et al.
1999; Sayer et al. 2003; Reid et al. 2005).
5.2.5 Inorganic-Organic Composite Biomimetic Bioceramics
CaP bioceramics have already been used in clinics for filling of bone defects
due to their bone-bonding ability with living tissue. However, the brittleness
and low fatigue strength in a physiological environment limit their use for
load-bearing repair or substitute. In recent years, composite materials com-
prised of bioactive inorganic CaP particles and organic (bio)polymers have
been studied, such as HAp/Col, HAp/PLA, and HAp/gelatin. Narbat et al.
(2006) studied the fabrication of porous hydroxyapatite-gelatin composite
scaffolds for bone tissue engineering. It was observed that the prepared scaf-
fold has an open, interconnected porous structure with a pore size of 80 to
400 µm, which is suitable for osteoblast cell proliferation. It was found that
the GEL/HAp with ratio of 50 wt% HAp has the compressive modulus of
~10 GPa, the ultimate compressive stress of ~32 MPa, and the elongation of
~3 MPa similar to that of trabecular bone. Wang et al. (2002) reported that the
nanoscale HAp (n-HAp)/PAA 66 composites were similar to bone apatite in
size, phase composition, and crystal structure. The biomimetic n-HAp crys-
tals were uniformly distributed in the polymer matrix and its content can
reach 65%, close to that in natural bone. Bending strength, tensile strength,
and impact strength of n-HAp/PA66 composite with a n-HAp content of 55
wt% were higher than those of µ-HAp/PA66 with the same HAp content,
increased by 31.3%, 38.9%, and 68.0%, respectively. The bending modulus of
n-HAp/PA66 composite is 6.2 GPa, similar to the range of natural bone (from
6.9 to 27.4 GPa).
In addition, the method to coat the porous CaP scaffold with a polymer
lining is appropriate to improve the mechanical properties of the intercon-
nected porous CaP scaffold, while the high porosity and interconnectivity is
maintained. Usually, synthetic polymers are preferable lining candidates to
a natural-based polymer for their predictable and reproducible degradation
characteristics as well as reasonable mechanical properties. For example,
polycaprolactone (PCL) is a synthetic biocompatible polymer with higher
fracture energy than other biopolymers. Thus, the porous HAp scaffold
coated with a PCL lining and biomimetic CaP to form a composite scaffold
can possess an improved toughening properties (Zhao et al. 2008).
5.3 Biomineralization of Bioceramics
Biomineralization, or biomimetic mineralization, refers to the process by
which living forms precipitate mineral materials. The common idea is that
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