Biomedical Engineering Reference
In-Depth Information
of the biomedical applications of ACP-containing biocomposites and
hybrid formulations are available in section
2.5
.
6.4.2
Calcium Orthophosphate Cement-Based
Biocomposites and Concretes
Inorganic self-setting calcium orthophosphate cements, which
harden in the body, were introduced by LeGeros et al. [516] and
Brown and Chow [517, 518] in the early 1980s [519]. Since then,
these cements have been broadly studied and many formulations
have been proposed (see Chapter 5 for the details). The cements
set and harden due to various chemical interactions among calcium
orthophosphates that finally lead to formation of a monolithic
body consisting of either CHDA or DCPD with possible admixtures
of other phases. Unfortunately, having the ceramic nature, calcium
orthophosphate cements are brittle after hardening and the
setting time is sometimes unsuitable for clinical procedures [519].
Therefore, various attempts have been performed to transform
the cements into biocomposites e.g., by adding hydroxylcarboxylic
acids, to control the setting time [520], gelatin to improve both
the mechanical properties and the setting time [473, 521-523]
or osteocalcin/collagen to increase the bioactivity [524]. More to
the point, various reinforcement additives of different shapes and
nature are widely used to improve the mechanical properties of
calcium orthophosphate cements (see section
for details). Even
carbon nanotubes were used for this purpose [525]! Although
the biomaterials community does not use this term, a substantial
amount of the reinforced cement formulations might be defined as
calcium orthophosphate-based concretes [526]. The idea behind the
concretes is simple: if a strong filler is present in the matrix, it might
stop crack propagation.
Various apatite-containing biocomposite formulations based
on PMMA [527-540] and PEMA [102, 541, 542] have been already
developed. Such biocomposites might be prepared by dispersion of
apatite powder into a PMMA viscous fluid [543] and used for drug
delivery purposes [544]. When the mechanical properties of the
concretes composed of PMMA matrix and HA particles of various
sizes were tested, the tensile results showed that strength was
independent on particle sizes. In addition, up to 40% by weight HA
could be added without impairing the mechanical properties [530,
5.7
Search WWH ::
Custom Search