Biomedical Engineering Reference
In-Depth Information
pattern consistent with a pure hexagonal crystal structure, although
the related
α
-TCP is monoclinic.
β
-TCP turns into
α
-TCP around
1200°C; the latter phase is considered to be stable in the range
700 to 1200°C.
β
-TCP is highly soluble in body luid.
To achieve an optimum resorbability of the material, studies
have mainly focused on the biphasic calcium phosphate ceramics
composed of HAP and TCP. Several results suggest that the
resorbability of biphasic ceramics is largely determined by the HAP/
TCP ratio.
Takatoshoi
et al
. examined the biocompatibility of calcium
phosphate bone cement for clinical use by an
in vitro
assay system
[126]. The experimental material was the bone replaceability
calcium phosphate cement (BRCPC, Norian PDC, Shofu). The obtained
results indicate that BRCPC has bioactivity such as osteogenesis.
On the other hand, BRCPC does not have cytotoxicity. Recently,
Bogdanski
et al
. investigated nickel-titanium shape memory
alloys (NiTi-SMA) [9]. These alloys have mechanical properties
(superelasticity, shape memory effect) that make them very
interesting for clinical applications. Due to the high nickel content
of the material, there are concerns about possible immunological
reactions of the surrounding tissue. The proliferation of osteoblast-
like cells (MG-63)
and
the cytokine release (interleukin (IL)-6, IL-8,
tumor necrosis factor (TNF)-a) from polymorphonuclear neutrophil
(PMN) leukocytes as well as peripheral blood mononuclear cells
(PBMC) in response to different NiTi specimen was studied: (a)
NiTi coated with calcium phosphate (octacalcium phosphate
+ hydroxyapatite; OCP/HAP) from an supersaturated aqueous
solution, consisting of a dense layer of sharp-edged platelets; (b) NiTi
coated with calcium phosphate (hydroxyapatite) by high-temperature
plasma-spraying, consisting of a rough dense layer of globular
particles; (c) NiTi after geometrical structuring (microdrilling). In
the irst two cases, the aim was to improve the biocompatibility
while retaining the mechanical properties. In the third case, the effect
of mechanical treatment (damage of the passivating TiO
2
surface
layer) was investigated. In comparison to non-coated samples, the
OCP/HAP-coated SMA led to an increase in the release of cytokines,
in contrast, the HAP-coated samples led to a decrease in cytokine
release from PBMC. The attachment, viability,
and
the proliferation
of MG-63-cells in the near vicinity of microdrilled structures were
not different from non-strained surface areas. These results show
