Biomedical Engineering Reference
In-Depth Information
some extent. Another limitation of synthetic materials is that they can not repair
themselves (wound healing) as living bone does.
Nevertheless, extensive efforts are still underway to develop and explore
various material combinations in the attempt to develop biocompatible materials.
The following sections present the structure and properties of Ca-P based
materials.
3.4 PROCESSING AND PROPERTIES OF BIOCERAMICS AND
BIOCERAMIC COMPOSITES
3.4.1 Calcium Phosphate Based Biomaterials
Calcium phosphate (CaP)-based ceramics offer great potential in many applica-
tions requiring bonding with the bone. The most popular bioactive calcium phos-
phate material is hydroxyapatite [with chemical composition of Ca 10 (PO 4 ) 6 (OH) 2 ],
having similar mineral composition of bone and teeth. In Figure 3.2, the stability
region of HAp in CaO-P 2 O 5 - H 2 O ternary system has been shown. A number of
compounds with varying Ca/P ratio, belonging to CaP family, are of relevance to
biomedical applications. These include octacalcium phosphate (OCP, Ca/P = 1.33),
tricalcium phosphate (TCP, Ca/P = 1.5), HAp (Ca/P = 1.67) and tetracalcium
phosphate (TTCP, Ca/P = 2). TCP can also exist in two polymorphs:
α
- TCP and
β
-TCP. While TCP and HAp are the commonly reported phases in CaP-based
materials, in vitro or in vivo formation of OCP or other phases are also reported
to a limited extent 10,11 . Between these two,
α
-TCP formation is favored at high
(P 2 O 5 )/2
A
H 2 O
D
Ca(OH) 2
CaO
Figure 3.2. Ternary Phase diagram of CaO-P 2 O 5 -H 2 O ternary system showing the stability
region of different CaP phases along with hydroxyapatite.
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