Biomedical Engineering Reference
In-Depth Information
13.13
The metal back of the cup from the same implant in Fig. 13.12;
the rationale for a degradable bioactive glass coating is to lead the
bone gradually to appose the metal without the production, at the
end, of bulky non-degradable particles.
Since the development of the first bioactive glass by Hench, several
kinds of glasses and glass-ceramics have been found to interface with living
bone. The model in this class of materials is Bioglass 45S5 of which the
composition in weight% is: 45% SiO
2
, 24.5% CaO, 6% P
2
o
5
and 24.5%
na
2
of The bonding mechanism of silicate bioactive glasses to bone has been
attributed to a series of surface reactions ultimately leading to the formation
of a hydroxycarbonate apatite layer at the glass surface. The critical element
necessary for the formation of this is the production of a layer of porous silica
gel with a high surface area. The apatite phase is formed when the bioactive
material comes into contact with the aqueous component of physiological
fluids.
Standardization of hydroxyapatite coating techniques for orthopaedic
implants has, probably, limited the exploitation of bioactive glass coatings
in orthopaedic surgery, while it is more applied in dental and maxilofacial
surgery.
13.3.6 Composites
Composite materials made from carbon fibres and epoxidic resins were
proposed for applications in orthopaedic surgery to promote the replacement
of metals (Fig. 13.14). This replacement process has happened in other fields,
like the aerospace industry, but in orthopaedic surgery the possible unmasking
of carbon fibres and their dispersion inside the body was an unacceptable
risk (Fig. 13.15). The high costs were also another big concern.
