Biomedical Engineering Reference
In-Depth Information
bioactive systems.
117-122
in this way, osseous integration is improved and
drug release is favoured, owing to the ionic interchange between the glass
and the medium.
SSg-magnetic glass-ceramic
materials were designed to treat osseous
tissues affected by tumours. thus, it should be possible to obtain bioactive
materials that are able to regenerate bone, with magnetic behaviour that
can be used in hyperthermia treatments. interstitial hyperthermia, based on
the higher sensibility to high temperatures of cancer cells, concentrates the
heat treatment to the desired volume without affecting healthy surrounding
tissues. Magnetic glass-ceramics act as thermoseeds, whereas SSg induce the
bioactivity.
123-130
However, SSg seems to partially inhibit the iron incorporation
into crystalline phases of glass-ceramic, consequently decreasing the magnetic
behaviour.
129, 130
at the present, the
in vitro
biocompatibility of these mixtures
has been established
131
and the
in vivo
behaviour is being studied.
SSg-Ha materials were designed to accelerate the bioactive response
of Ha.
132
Biphasic SSg-Ha mixtures exhibit higher bioactivity than pure
Ha.
133-136
the addition of a 5% bioactive glass noticeably increases the
bioactive response of HA. Thus, a mixture 30%CaO-70%SiO
2
glass/HA
was covered with a HCa layer after 12 hours in SBF, whereas the surface
of pure HA was not modified even after 45 days of immersion. To reach
high reactivity in aqueous solutions, Ha powders with particle sizes in the
range 0.1-50 mm were used. after the sintering process of Ha and dry
gels, biphasic mixtures with an average particle size around 30 mm were
obtained. another interesting feature of these bioceramics is that the HCa
layers formed after the
in vitro
studies are more homogeneous than those
formed on pure sol-gel glasses.
7.3.3 Glass-ceramics
glass-ceramics are crystalline materials nucleated within and from a glass.
the formation of these materials is initiated for the addition of nucleating
agents that help to nucleate and grow small crystals uniformly distributed
within the glass matrix. these nucleating agents can be metals such as Cu,
Ag, Au or Pt and oxides like TiO
2
, ZrO
2
or P
2
O
5
. the nucleation process
takes place at temperatures lower than the melting temperature and further
annealing is conducted at appropriate temperatures to cause uniform crystal
growth. the nucleating agents and the heat treatment temperatures help to
control grain size to 0.1-1 mm. the resultant glass-ceramic acts as a composite
with crystalline phases actuating as a reinforced component, thus, it exhibits
superior mechanical properties to the parent glass and to sintered crystalline
ceramics. actually monophase bioactive ceramics, such as glasses or sintered
Ha, do not show as high a mechanical strength as human cortical bone as
is observed in table 7.5.
