Biomedical Engineering Reference
In-Depth Information
said to be perfectly biocompatible, resorbable and easily fitted bone
defects (due to an initial plasticity) [108, 894, 898-905]. The best
ratio BCP/HPMC aqueous solution was found to be at ~ 65/35 w/w.
To extend this subject further, IBS might be loaded by cells [906,
907], radiopaque elements [908] or microparticles [909], as well as
functionalized by nucleic acids [890]. Self-hardening formulations,
based on Si-HPMC hydrogel, are known as well [906]. The list of
the commercially available calcium orthophosphate-based IBS
formulations is presented in Table 6.4 [910].
The advanced characteristics of IBS come from their good
rheological properties and biocompatibility and the ease of tissue
regeneration. Although the fabrication of IBS biocomposites in
most cases improved the mechanical properties of the system
and provided the material with resistance to fluids penetration,
these achievements were limited by the amount of polymer that
can be added to the paste. For instance, Mickiewicz et al
reported
that after a critical concentration (that depended on the type and
molecular weight of the polymer, but was always around 10%),
the polymer started forming a thick coating on the crystal clusters,
preventing them from interlocking, originating plastic flow and, as a
consequence, decreasing mechanical properties [561]. More to the
point, Fujishiro et al
.
reported a decrease in mechanical properties
with higher amounts of gel, which was attributed to formation of
pores due to leaching of gelatin in solution [554]. Therefore, it seems
that mechanical properties, although improved by the addition
of polymers, are still a limitation for the application of calcium
orthophosphate-based IBS formulations in load-bearing sites [178].
Further details on IBS might be found in a recent review [892].
.
6.4.7
Biocomposites with Glasses, Inorganic Materials,
Carbon and Metals
To overcome the problem of poor mechanical properties of calcium
orthophosphate bioceramics, suitable biocomposites of calcium
orthophosphates reinforced by various inorganic materials, glasses,
and metals have been developed. Such biocomposites are mainly
prepared by the common ceramic processing techniques such as
thermal treatment after kneading [911-913], powder slurry coating
[914] and metal-sol mixing [915]. For example, HA was combined
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