Biomedical Engineering Reference
In-Depth Information
of apposition and removal that occurs in living bone (Tranquilli leali
et al
.,
1994). This behaviour well deserves the name 'biomimicry' (Williams, 1995).
Then, coating an implant with hydroxyapatite became an effective system
for masking the structural material which it is made of, promoting an early
favourable response from recipient bone towards the implant (Fig. 13.10).
Hydroxyapatite is also used as bone filler when large cavities are
encountered. it must be underlined that, in this role, the complete resorption
of the implanted material is not always obtained, even in the long term (Fig.
13.11); furthermore, hydroxyapatite can be used as a filler only when no real
mechanical task is required.
other bioactive ceramic materials, like the calcium phosphates, have been
proposed and are now in clinical use, using basically the same principles
outlined for hydroxyapatite.
13.3.5 Glasses
In the 1970s, Prof. Larry Hench discovered that a particular range of glass
composition could elicit a favourable bone cells growth (Hench
et al
., 1971).
A particular application in orthopaedic surgery came from the deposition
of a bioactive glass coating in a similar fashion to hydroxyapatite coating
(Merolli
et al
., 1999). The rationale for a degradable bioactive glass coating
13.10
A low magnification (X15) back scattered electron micrograph
which shows trabecular bone growing in apposition to a
hydroxyapatite coated metallic rod, in an experimental model in the
rabbit.
