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Hydroxyapatite Mineralization on the Surface of the
Crosslinked PStBP Particles
situ, the tri-sodium salt back to the free acid. The characteri-
zation of these crosslinked PStBP particles was accomplished
by routine methods such as FTIR, TGA, and DSC. The adsorp-
tion effect of the StBP monomer on HAP was examined by
solid-state MAS 31P NMR spectroscopy and was found to be
similar to commercial BPs (Alendronate). The mineralization
process of the crosslinked PStBP particles versus PS particles
was studied. Only the new hydroxyBPs particles formed
crosslinked PStBP-HAP hybrid particles as was demonstrated
by TEM images. These results indicate that the StBP mono-
mer and crosslinked PStBP particles have a unique high af-
finity to HAP. Consequently, these nonbiodegradable StBP
monomer and crosslinked PStBP particles may be good can-
didates for dental and bone applications. For future studies,
we plan to extend this work and investigate the efficiency of
the StBP monomer and crosslinked PStBP particles for vari-
ous biomedical applications.
The study of the adsorbed effect of HAP crystals on the
crosslinked PStBP particles was based on Francis35 and
Golomb’s36 previous works. The principle of this method
relies on the ability of the crosslinked PStBP particles to
create chelate with the free calcium ions in the supersatu-
rated solution followed by phosphate ions adhesion to the
formed HAP-conjugated crosslinked PStBP particles. PS par-
ticles, without the hydroxyl-bisphosphonic function, served
as a control study for HAP precipitation. Each ꢂtype of parti-
cle, crosslinked PStBP or PS, was shaken at 37 C in a super-
saturated calcium phosphate solution for 24 h. The resulted
precipitation was separated and sonicated in fresh water.
Samples from this mixture were analyzed by TEM.
Figure 9 illustrates TEM pictures of crosslinked PStBP par-
ticles (A), crosslinked PStBP particles after HAP mineraliza-
tion (B, D, and E) (image E represents a higher magnification
of image B) and PS particles after incubation in supersatu-
rated calcium phosphate solution (C). Incubation of the sus-
pended crosslinked PStBP particles resulted in precipitation
of crosslinked PStBP-HAP hybrid particles. The first step in
the mineralization process is the chelation of the calcium
ions by the hydroxy-bisphosphonate’s surface groups of the
particles. The newly formed calcium-conjugated crosslinked
PStBP particles precipitate and grow to be the nuclei of a
composed material consisting of the crosslinked PStBP-HAP
hybrid particles. In Figure 9(B,D,E), the organic crosslinked
PStBP particles are presented as dark, round spots while the
inorganic HAP crystals are in white. Figure 9(A) shows that
the crosslinked PStBP particles touch each other, probably
due to strong hydrogen bonds between the oxygen and the
hydrogen atoms of the hydroxyl-bisphosphonic function. Fig-
ure 9(B,D,E) illustrates that the crosslinked PStBP particles
are surrounded by HAP crystals. As mentioned, this is due to
the strong interaction of the crosslinked PStBP particles with
the calcium ions. It is interesting to note that in this case the
distance between the crosslinked PStBP particles increased
relative to the distance shown in Figure 9(A). The increased
distance probably results from the ionic bonds formed
between the HAP and the hydroxyBPs surface groups of the
crosslinked PStBP particles that replace the hydrogen bonds
existing between the crosslinked PStBP particles in the ab-
sence of HAP. In contrast, most of the PS particles remained
suspended in the experimental solution and did not precipi-
tate like the crosslinked PStBP particles. Figure 9(C) exhibits
PS particles that did precipitate and which are not sur-
rounded by HAP crystals.
ACKNOWLEDGMENTS
The authors thank Prof. Eli Breuer for fruitful discussions, Dr.
Rachel Persky for MS analysis, and Dr. Hugo Gottlieb and
Dr. Keren Keinan-Adamsky for NMR analysis.
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