Biomedical Engineering Reference
In-Depth Information
biodegradation of calcium orthophosphate
bioceramics is estimated by suspending the material in a slightly acidic
(pH ~5) buffer and monitoring the release of Ca
Usually, an
in vitro
2+
ions with time. The
acidic buffer, to some extent, mimics the acidic environment during
osteoclastic activity. In one study, an
behavior of porous β-TCP
bioceramics prepared from rod-shaped particles and that prepared
from non-rod-shaped particles in the rabbit femur was compared.
Although the porosities of both types of β-TCP bioceramics were
almost the same, a more active osteogenesis was preserved in the
region where rod-shaped bioceramics was implanted [634]. This
result implied that the microstructure affected the activity of bone
cells and subsequent bone replacement.
The experimental results demonstrated that both the dissolution
kinetics and
in vivo
biodegradation of biologically relevant calcium
orthophosphates proceed in the following decreasing order: β-TCP >
bovine bone apatite (unsintered) > bovine bone apatite (sintered) >
coralline HA > HA. In the case of BCP bioceramics, the biodegradation
kinetics depends on the HA/TCP ratio: the higher the ratio, the lower
the degradation rate. Similarly,
in vivo
degradation rate of biphasic
TCP (α-TCP + β-TCP) bioceramics appeared to be lower than that of
α-TCP and higher than that of β-TCP bioceramics, respectively [138].
Furthermore, incorporation of doping ions can either increase (e.g
in vivo
.
,
3 2−
2+
2+
CO
) the solubility (therefore,
biodegradability) of CDHA and HA. Contrarily to apatites, solubility
of β-TCP is decreased by incorporation of either Mg
, Mg
or Sr
) or decrease (e.g
.
, F
2+
2+
or Zn
ions [459]. Here, one should remind that ion-substituted calcium
orthophosphates are not considered in this review; the interested
readers are advised to read the original publications [8-38].
4.6.4
Bioactivity
Generally, bioactive materials interact with surrounding bone
resulting in formation of a chemical bond to this tissue (bone
bonding). The bioactivity phenomenon is determined by both
chemical factors, such as crystal phases and molecular structures
of a biomaterial, and physical factors, such as surface roughness
and porosity. Currently, it is agreed that the newly formed bone
bonds directly to biomaterials through a carbonated CDHA layer
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