Biomedical Engineering Reference
In-Depth Information
2010b
; Barth
2010
; Kester
2008
; Morgan
2008
; Muddana
2009
; Russin
2010
). The
reverse micelle synthetic route also permits the formation of well-dispersed nano-
colloids that can be bio-conjugated to target molecules for specific cancers (Barth
2010
). Adair and co-workers have reported in a series of manuscripts the efficacy
of drugs and bioimaging agents encapsulated within the CPSNP.
2.2
pH Dependent Solubility of Calcium Phosphates
In addition to the biocompatibility and bioresorbability of calcium phosphate, the
unique chemistry of the material system enables tunability of properties and hence
versatility in applications. CP exists in a variety of crystalline and amorphous
phases primarily dependent on the conditions under which the particles are formed
and subsequent processing. ACP can be stabilized by the addition of species includ-
ing Mg
2+
and Zn
2+
(Bertoni
1998
; Bigi
1993, 1995
; Rokita
1993
). Additionally, the
pH dependent solubility of calcium phosphates as shown in Fig.
1
underscores the
Fig. 1
pH dependent solubility behavior of calcium phosphates.
As pH increases to more
basic values calcium phosphate becomes increasingly insoluble. In contrast, as the pH approaches
the acidic regime, calcium phosphate becomes increasingly soluble. The different phases of cal-
cium phosphate represented above are:
DCPD
- dicalcium phosphate dihydrate,
OCP
- octacal-
cium phosphate,
TCP
- tricalcium phosphate and
HAP
- hydroxyapatite. The highly metastable
amorphous phase and the less soluble amorphous calcium phosphosilicate phases are not shown.
All phases of calcium phosphate become increasingly soluble below pH 6. This pH dependent
behavior makes calcium phosphate an ideal encapsulating agent for drug and imaging agents -
dissolution with release of the active agent occurs as pH decreases within the cell (Modified from
Chow (
1991
). With permission)
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