Biomedical Engineering Reference
In-Depth Information
room temperature. An injectable paste is obtained which sets in
less than 20 min at 37°C. After hardening, the cement is constituted
of nanocrystalline CDHA with crystal dimensions close to those in
human bones [31]. A similar formulation but additionally containing
mechano-activated β-cyclodextrins has been studied as well [155].
Furthermore, a self-setting ACP + DCPA formulation is known
[283]. Besides, ACP might be added as an admixture phase to the
standard calcium orthophosphate cement formulations [44, 284]. In
such cases, addition of ACP resulted in cements exhibited shorter
setting times, a compressive strength suitable for non-load-bearing
applications and the full conversion to nanocrystalline CDHA.
Moreover, ACP-containing formulations demonstrated good cell
viability, making them suitable candidates for biomedical applications
[284]. More to the point, nano-sized particles of 13, 19, and 40 nm
diameter of amorphous TCP were found to be highly reactive and
set to CDHA within minutes, which is much faster if compared with
microcrystalline powders of both α-TCP and β-TCP [187, 188]. A
similar approach was reported in other studies [156-158].
Since ACPs do not sustain heating above ~ 600°C (see section
2.3.6), a possibility of preparing dense ACP bioceramics was studied
using spark plasma sintering technique at temperatures ranging
from 150 to 200°C with the processing time < 15 min. Unfortunately,
the observed mechanical strength of the prepared consolidated disks
(sintered for 6 min at 150°C) was poor [285]. However, an increase
in the sintering processing time to 13 min indicated to a possibility
of improving the mechanical properties. The low temperature
conditions appeared to be more adaptive to the processing of ACP
when compared with the experimental conditions of conventional
sintering. However, the physicochemical characterization of the
prepared consolidated bioceramics indicated a crystallization of the
initial ACP to an apatitic phase with no other detectable crystalline
phase [31].
However, the majority of cases of the biomedical applications
of ACPs comprise various biocomposites and hybrid biomaterials
containing ACP as one of the phases [48-75, 155, 286-300]. Several
ACP-containing formulations (e.g., Recaldent™ and Enamelon™)
are now commercially available [299]. As can be seen from the
references, most of the applications are in dentistry field. In all
cases, addition of calcium orthophosphates, including ACPs, imparts
both biocompatibility and bioactivity of the biocomposites [290].
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