Page 5 - PR 2014 2016 10 Materials and Nanotechnology

Materials and Nanotechnology | Progress Report 281
non-diluted extract was 97.5%, by reason of
this, the samples were considered non cyto-
toxic. No toxic effect of the prepared material
was found in the cytotoxicity test with CHO
(Chinese hamster ovary) cells.
A new modified sol gel method to preparing
CaO-MgO-SiO ceramic powder was presented.
2
Use of low-cost Na SiO is attractive to sub- used as sintering aids as well as to obtain a
2 3
stitute the usual high-cost TEOS as Si source.
According to ISO 10993-5, the obtained ma-
terial can be considered non cytotoxic.
Silicon Nitride Ceramics for Bone
Compatibility
In view of the growing demand to perform
different procedures for bone regeneration,
silicon nitride based ceramics are increas-
ingly being considered for applications in
biomedicine. This interest is justified by the
propitious mechanical properties, osseointe-
gration, bactericidal capacity and adequate
image characteristics - which allow implant
visualization through techniques such as
X-rays, computed tomography and magnetic
resonance imaging.
On the other hand, the bioinert character-
istics of the silicon nitride ceramics, whose
biological response does not lead to chemical
bonds with the host tissue, have motivated
us to develop dense and bioactive composites
with great mechanical properties.
As it is known, the production of dense silicon
nitride ceramics by the conventional sintering
method requires using additives, in order to
promote the liquid phase sintering, which
remains in the silicon nitride grain boundar- secondary phase, as well as non citotoxicity.
ies as an amorphous or partially crystalline
secondary phase. Thus, the production of
dense and bioactive silicon nitride ceramics is
based on the proper selection of the sintering
aids. The selected additives must promote
densification and a microstructure formed
by elongated β-Si N grains dispersed in a
3 4
bioactive phase formed by the solidification
of the liquid phase during the cooling step of
the sintering process.
In this study, silicon and calcium oxides were
secondary phase containing P O free bioac-
2 5
tive glasses, so that the contact with the physi-
ological fluids favors the apatite deposition on
the final material surface due to formation of
Si-OH groups. Samples with 80 or 90 wt.% sili-
con nitride and different contents of additives
were obtained by pressureless sintering and
characterized in regard to apparent density
by the Archimedes method. The crystalline
phases formed in the grain boundaries and
the α➔β-Si N transformation were evaluated
3 4
by the X-ray powder diffraction. The morphol-
ogy, grain size and phases distribution were
analyzed by scanning electron microscopy.
Also, The Young modulus was determined
by a non-destructive dynamic method, while
the hardness and fracture toughness were
determined using the Vickers indentation
method.
In vitro, cytotoxicity tests were performed
by the indirect method as suggested in ISO
10993-5, using fibroblast cell line (Balb/c). Bio-
activity studies in SBF (Simulated Body Fluid)
and osteoblast adhesion tests with MG63 line
cells were carried out on the samples.
The results showed that samples reached
high densification, microstructure formed by
β-Si3N4 grains dispersed in an intergranular
The materials also presented relatively high
values of fracture toughness and lower values
of Young modulus than those found for these
ceramics with conventional compositions.