Page 289 - 00. Complete Version - Progress Report IPEN 2014-2016

Materials and Nanotechnology | Progress Report 289

ered non cytotoxic. The cell viability of the on the proper selection of the sintering aids.
non-diluted extract was 97.5%, by reason of The selected additives must promote densifi-
this, the samples were considered non cyto- cation and a microstructure formed by elon-
toxic. No toxic effect of the prepared material gated ο-Si3N4 grains dispersed in a bioactive
was found in the cytotoxicity test with CHO phase formed by the solidification of the liq-
(Chinese hamster ovary) cells. uid phase during the cooling step of the sin-
tering process.
A new modified sol gel method to prepar-
ing CaO-MgO-SiO2 ceramic powder was pre- In this study, silicon and calcium oxides were
sented. Use of low-cost Na2SiO3 is attractive used as sintering aids as well as to obtain a
to substitute the usual high-cost TEOS as Si secondary phase containing P2O5 free bioac-
source. According to ISO 10993-5, the obtained tive glasses, so that the contact with the phys-
material can be considered non cytotoxic. iological fluids favors the apatite deposition
on the final material surface due to formation
Silicon Nitride Ceramics of Si-OH groups. Samples with 80 or 90 wt.%
for Bone Compatibility silicon nitride and different contents of ad-
ditives were obtained by pressureless sinter-
In view of the growing demand to perform dif- ing and characterized in regard to apparent
ferent procedures for bone regeneration, sil- density by the Archimedes method. The crys-
icon nitride based ceramics are increasingly talline phases formed in the grain boundar-
being considered for applications in biomed- ies and the οοο-Si3N4 transformation were
icine. This interest is justified by the propi- evaluated by the X-ray powder diffraction.
tious mechanical properties, osseointegration, The morphology, grain size and phases dis-
bactericidal capacity and adequate image tribution were analyzed by scanning elec-
characteristics - which allow implant visu- tron microscopy. Also, The Young modulus
alization through techniques such as X-rays, was determined by a non-destructive dynam-
computed tomography and magnetic reso- ic method, while the hardness and fracture
nance imaging. toughness were determined using the Vick-
ers indentation method.
On the other hand, the bioinert characteris-
tics of the silicon nitride ceramics, whose bi- In vitro, cytotoxicity tests were performed
ological response does not lead to chemical by the indirect method as suggested in ISO
bonds with the host tissue, have motivated 10993-5, using fibroblast cell line (Balb/c). Bio-
us to develop dense and bioactive composites activity studies in SBF (Simulated Body Fluid)
with great mechanical properties. and osteoblast adhesion tests with MG63 line
cells were carried out on the samples.
As it is known, the production of dense silicon
nitride ceramics by the conventional sintering The results showed that samples reached
method requires using additives, in order to high densification, microstructure formed by
promote the liquid phase sintering, which re- ο-Si3N4 grains dispersed in an intergranular
mains in the silicon nitride grain boundaries secondary phase, as well as non citotoxicity.
as an amorphous or partially crystalline sec- The materials also presented relatively high
ondary phase. Thus, the production of dense values of fracture toughness and lower values
and bioactive silicon nitride ceramics is based of Young modulus than those found for these