Biomedical Engineering Reference
In-Depth Information
formation is slower, but the HCa nanocrystals are detected quicker than in
CaO-SiO
2
glasses. these differences were explained in the nanostructural
characterization.
108
P
2
O
5
-free glasses contain numerous calcium ions in the
network that can interchange with protons in the SBF to form additional silanol
groups, facilitating amorphous calcium phosphate formation. However, the
HCA crystallization required more time. In P
2
O
5
-containing glasses, calcium
is strongly bonded in the Si-doped b-TCP nanocrystals and is difficult to be
released to SBF. thus, the formation of the amorphous calcium phosphate is
slower. However, once this phase is formed, Si-doped b-TCP nanocrystals
accelerate HCa crystallization. Furthermore, sol-gel glasses exhibited excellent
biocompatibility in both cell culture studies
109
and in animal models.
110-112
the high bioactivity of sol-gel glasses makes them excellent candidates to be
used in coatings, mixed materials or as porous scaffolds in third generation
biomaterials.
Bioactive glass coatings
as it was indicated in the section discussing calcium phosphate coatings
above, many techniques can be used to obtain ceramic coatings on metallic
substrates including PLD, PVD, CVD, plasma spray and so on. Taking
advantage of sol-gel technology, bioactive glass coatings have been obtained
by dip coating
.
this method allows the porosity, roughness and composition
of the bioactive film formed to be controlled. Simultaneously, the metallic
surface is protected from the biological environment. Coatings of a bioactive
glass with a composition of 20%CaO-80%SiO
2
(mol-%) on Ti6Al4V were
obtained.
113, 114
after 14 days, the acellular SBF coatings were completely
dissolved. First, the calcium ions and then the silica in the coatings leached
into the solution. it seems that the extreme reactivity of sol-gel glasses can be
a drawback in coatings when compared with Ha. However, when analogous
studies were performed in the presence of osteoblasts, the coatings remained
stable and, simultaneously, an increase of the cellular parameters (adhesion,
proliferation, differentiation, spreading) was observed.
115
in addition, the
influence of the substrate in the synthesis of sol-gel glasses coatings was
also evaluated. When coatings on 316L stainless steel were obtained, the
silicon in the glass bonded to chromium in the substrate during the dip coating
synthesis, with a subsequent increase in corrosion of the metallic alloy.
116
Mixed materials containing bioactive sol-gel glasses
Mixed materials systems containing a bioactive SSg to induce or increase
bioactivity were investigated including SSg-polymer-drug, SSg-magnetic
component and SSg-Ha.
SSg-polymer-drug
materials were designed to obtain controlled release
