Biomedical Engineering Reference
In-Depth Information
in comparison to bone may allow too much bone motion for sat-
isfactory healing, and reinforcement therefore is essential. Polymeric
self-reinforced screws showed higher tensile and bending strength in
comparison with homogeneous polymeric screws; however, the elastic
moduli were still too low, resulting in bending of the screws, which
limited their use.
As an alternative, degradable polymers can be reinforced with phos-
phate glass fibres. Reinforcement by glass fibres is of interest as
the fibres maintain stability and mechanical properties during later
states of polymer degradation. Indeed, glass-fibre-reinforced composites
offer excellent strength and stiffness, and continuous phosphate glass-
fibre-reinforced degradable polymer composites can have mechanical
properties suitable for fixing cortical bone fractures [16, 17], with elastic
moduli between 15 and 40 GPa.
4.8 APPLICATIONS
Although the importance of phosphate glasses compared to bioactive
silicate glasses has been small so far, their solubility, which ranges
over several orders of magnitude and can be tailored by changing the
glass composition, makes them a promising class of materials in the
field of biomedical materials. By making glass fibres or sintered porous
scaffolds, substrates for a variety of applications can be produced. There
is great interest in the development of phosphate glasses, and particularly
degradable phosphate glass-polymer composites, for application in bone
fracture fixation and hard tissue regeneration. The aim is to develop an
implant material that slowly degrades in the body, to be replaced by
newly formed natural bone. Controlling the glass solubility is a key issue
here in order to match the resorption rate of the implant to the rate of
bone growth.
Also, for soft tissue applications such as engineering of ligament, mus-
cle or cartilage regeneration, the use of phosphate glasses, for example
as fibres, meshes or in composites, would be of interest. It has further
been suggested that degradable phosphate glasses could potentially be
used for nerve regeneration and neural repair [1]. Despite a significant
increase in research output on phosphate glasses for biomedical appli-
cations, however, further research is necessary to optimise the materials
for in vivo applications.
Fluoride-releasing phosphate glass-based devices for prevention of
dental cavities are giving promising results for controlling caries in
children [18]. Low levels of fluoride are known to prevent enamel
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