Bioactive Glass as Synthetic Bone Grafts and Scaffolds for Tissue Engineering - Bio-Glasses: An Introduction - page 173

100 μ m

(a) (b)

Figure 12.1 Scanning electron microscope images of commercial synthetic bone
grafts: (a) NovaBone and (b) Actifuse.

Bioactive glass began commercial life as a particulate bone filler in
dental applications in 1995 and then became an orthopaedic product a
few years later. Surgeons mix the sachet of bioactive glass powder with
blood from the bone defect of the patient and push the mixture into
the defect as a putty. One of the main problems for lack of widespread
use of bioactive glass in orthopaedic applications has been the lack
of products available. Several compositions, such as Bioglass ® -the
original Hench formulation - available as PerioGlas ® and NovaBone ®
(NovaBone Products, USA), Biogran ®

(Orthovita, USA), BonAlive ®

(BonAlive, Finland) and StronBone (RepRegen, UK) exist, but they

are all particulates (Figure 12.1a). So let us take a look at the current
market-leading synthetic bone graft: Actifuse ® (Apatech, UK). Actifuse
is a synthetic hydroxyapatite. What sets it apart from other synthetic
hydroxapatites (of which there are many commercial products) is that
it contains a small amount (0.8wt%) of silicon. It is silicon-substituted
hydroxyapatite. Traditional synthetic apatites are highly crystalline
ceramics that degrade slowly and bond to bone slowly. The small
amount of silicon in the Actifuse formulation creates defects, increasing
the number of grain boundaries and reducing crystallinity just enough to
increase degradation. Silicon was chosen because of studies that showed
that a diet containing silicon is necessary for healthy bone growth and
because bioactive glass was known to be more bioactive than the bioac-
tive ceramics. One reason for the latter was that the glasses release

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