Biomedical Engineering Reference
In-Depth Information
converted into those of ACP and CDHA by supplementary treatment
of the oxide network in alkaline solutions [461]. Hollow nano-sized
shells of undisclosed calcium orthophosphates (presumably, of ACP)
with a size distribution of (120-185) ± 50 nm and predictable mean
shell thickness from 10 to 40 nm were prepared by crystallization
onto the surface of nanodimensional liposomes [462, 463]. Both
the suspension stability and shell thickness control were achieved
through the introduction of carboxyethylphosphoric acid. Variation
of shell thickness and stoichiometry may be a way of manipulating
the dissolution kinetics of ACP coating to control the release of
encapsulated materials, necessary for drug delivery purposes [462,
463]. Roughly spherical DCPA particles of approx. 50-100 nm in
sizes were synthesized via a spray-drying technique [106, 464-466],
while ribbon-like fibers of nano-sized DCPA might be prepared upon
hydrolysis in urea [357]. Furthermore, nanodimensional calcium
orthophosphate powders with DCPD as the major phase have been
synthesized by an inverse microemulsion system using kerosene as
the oil phase, a cationic surfactant and a non-ionic surfactant [467].
Microskeletal constructions might be synthesized as well [468].
When it comes to ACP, it is nanodimensional in the vast majority
cases (Chapter 2). Approximately spherical nano-sized particles
of ACP with a diameter of about 50 nm can be prepared by rapid
precipitation from water and subsequent colloidal stabilization
by coating with polymers [469]. Nano-sized clusters of ACP [470]
or those comprising a spherical core of 355 ± 20 DCPD units with
density of 2.31 g/cm
3
and radius of 2.30 ± 0.05 nm surrounded by
49 ± 4 peptide chains with a partial specific volume of 0.7 cm
3
/g,
forming a tightly packed shell with an outer radius of 4.04 ± 0.15 nm
were prepared by precipitation using 10 mg/ml of the 25-amino-
acid N-terminal tryptic phosphopeptide of bovine β-casein as a
stabilizing agent [471]. Nano-sized particles of ACP were prepared
by mixing of solutions of Ca(NO
)
·4H
O (450 mmol/L) in acetone
3
2
2
and (NH
(30 mmol/L) in deionized water at pH within 10.0-
11.0 [472]. Furthermore, nanodimensional powders of ACP might
be prepared by both an electrostatic spray pyrolysis [473, 474] and
spray drying [106] techniques.
Self-assembled shell cross-linked poly(acrylic acid-b-isoprene)
micelles and/or cross-linked poly(acrylic) acid nano-sized cages in
aqueous solutions might be used as templates for preparation of
polymer/calcium orthophosphate nanodimensional capsules of 50-
)
HPO
4
2
4
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