Biomedical Engineering Reference
In-Depth Information
as a template for mineral formation. Different hydrogels have been used,
including agarose, acrylamide and gelatin (for a review, see Silverman
et al. [76]). One of the most promising biomacromolecules identifi ed by
these analytical test systems is bone sialoprotein (BSP), which was shown
to promote mineralization of agarose [77] and gelatin [78] hydrogels.
Potentiation of the mineralization-promoting effect of biomacromolecules
by the hydrogel has been observed: BSP has promoted mineral formation
more effectively in collagen hydrogels than in agarose [79] and gelatin [80].
From a fundamental research point of view, this suggests that hydrogel-
biomacromolecule interactions should be taken into account when design-
ing test systems. From the point of view of practical applications, this
shows that the mineralization-promoting effect of biomacromolecules
may be enhanced if they are combined with a suitable hydrogel. In another
test system, Chirila et al. covalently immobilized artifi cially synthesized
proteins containing nacrein motifs onto the surface of PHEMA hydrogels,
which resulted in enhanced calcium uptake and CaP formation after incu-
bation in a mineralization medium containing CaCl 2 and Na 3 PO 4 [81].
3.5.2
Biomacromolecule-Enhanced Mineralization for Bone
Regeneration Applications
While biomacromolecules examined in studies in the fi rst category have
generally originated from mammalian bone or hard tissue extracellular
matrix, those in the second, application-orientated category are mainly
of non-ECM origin. In general, these biomacromolecules have already
shown affi nity for calcium ions in non-biomaterial-related systems.
Dragusin et al. incorporated casein, a phosphoprotein found in milk
and known to be a delivery vehicle for calcium, into PHEMA hydrogels to
induce mineralization under physiological conditions [82]. After incuba-
tion in SBF, CaP formation occurred on regions rich in casein.
Fibroin, a protein created by silkworms in the production of silk, has
regulated the formation of hydroxyapatite [83]. Zaharia et al. created
hybrid hydrogels consisting of interpenetrating networks of silk fi broin
and polyacrylamide [84]. Increasing the silk fi broin:polyacrylamide ratio
led to increased formation of mineral deposits when hydrogels were
incubated in SBF. Marelli et al. non-covalently incorporated different silk
fi broin-derived polypeptide fragments into dense collagen hydrogels to
compare their ability to promote mineralization during incubation in SBF
[85]. Hydrophobic crystalline polypeptides proved effective in inducing
apatite formation, in contrast to hydrophilic electronegative polypeptides,
which did not promote mineralization.
The polysaccharide alginate, which possesses a high affi nity for cal-
cium ions due to its high negative charge density, has been added to
hydrogels to promote mineralization. Stancu et al. added sodium alginate
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