Calcium Orthophosphates as Bioceramics - Calcium Orthophosphates: Applications in Nature, Biology and Medicine - page 347

bioceramics are available elsewhere [233, 325], where the interested
readers are referred to.

4.4.2 Electrical Properties

Occasionally, an interest to the electrical properties of calcium
orthophosphate bioceramics is expressed. For example, a surface
ionic conductivity of both porous and dense HA bioceramics
was examined for humidity sensor applications, since the room
temperature conductivity was influenced by relative humidity [326].
Namely, the ionic conductivity of HA has been a subject of research
for its possible use as an alcohol [327], carbon dioxide [327] or
carbon monoxide [328] gas sensors. Electrical measurements have
also been used as a characterization tool to study the evolution of
microstructure in HA bioceramics [329]. More to the point, Valdes
et al. examined the dielectric properties of HA to understand its
decomposition to β-TCP [330]. In the case of CDHA, the electrical
properties, in terms of ionic conductivity, were found to increase
after compression of the samples at 15 t/cm

2

, which was attributed
to establishment of some order within the apatitic network [331].
The conductivity mechanism of CDHA appeared to be multiple
[332]. Furthermore, there was an attempt to develop CDHA whisker
electrets for biomedical utilization [333].
Interestingly, but the electrical properties of calcium
orthophosphate bioceramics appear to influence their biomedical
applications. For example, there is an interest in polarization of
HA bioceramics to generate a surface charge by the application of
electric fields at elevated temperatures [334, 335]. The presence of
surface charges on HA bioceramics was shown to have a significant
effect on both crystallization of biological apatite

[336-340]. Furthermore, a growth of both biomimetic calcium
orthophosphates and bones was found to be accelerated on negatively
charged surfaces and decelerated at positively charged surfaces
[340-349]. In addition, the electrical polarization of HA bioceramics
was found to accelerate a cytoskeleton reorganization of osteoblast-
like cells [350-352], extend bioactivity [353] and enhance bone
ingrowth through the pores of porous HA implants [354]. There is
an interesting study on the interaction of a blood coagulation factor
on electrically polarized HA surfaces [355]. Further details on the
electrical properties of calcium orthophosphate-based bioceramics
are available in literature [279, 356-360].

in vitro and in vivo