Phosphate Glasses - Bio-Glasses: An Introduction - page 62

demineralisation, enhance remineralisation and inhibit the metabolism
of acidogenic bacteria such as mutans streptococci and lactobacilli [19].
Fluoride-releasing phosphate glass pellets are attached to molars, and
while the glasses continuously degrade inside the oral cavity, they release
fluoride, thereby allowing for low levels of fluoride to be maintained in
the mouth.
The ability of phosphate glasses to release ions upon degradation
can also be used in the development of materials for controlled release
of therapeutically active ions, such as strontium-releasing glasses for
treatment of osteoporosis, or for release of antibacterial ions such as
copper, zinc or silver [9].
In addition to medical uses, there are other applications where the
solubility of phosphate glasses is of interest; and phosphate glasses are
used as fertilisers in agriculture and for treating trace-element deficiency
in cattle [20]. In the latter case, glass boluses are placed in the animals'
stomachs, where they give a sustained release of ions (e.g. cobalt, copper,
selenium or zinc) over time.
4.9 SUMMARY
Phosphate glasses are soluble in aqueous solution, and can have a
composition similar to mineralised tissue, which makes them of interest
for use as degradable materials for bone regeneration, but also for use
as materials for controlled release of ions in therapeutic concentrations.
Glass solubility is closely related to its composition and structure,
and controlling degradation and ion release are critical for successful
applications of these materials. Composite materials based on degradable
polymers such as PLA and phosphate glasses are a promising way of
modulating the mechanical properties to match them to the surrounding
tissue in the body.
REFERENCES
[1] Knowles, J.C. (2003) Phosphate based glasses for biomedical applications. Journal
of Materials Chemistry , 13 , 2395-2401.
[2] Carta, D., Knowles, J.C., Guerry, P. et al . (2009) Sol-gel synthesis and structural
characterisation of P 2 O 5 -B 2 O 3 -Na 2 O glasses for biomedical applications. Journal
of Materials Chemistry , 19 , 150-158.
[3] van Wazer, J.R. (1958) Phosphorus and its Compounds . New York: Interscience.
[4] Brow, R.K. (2000) Review: the structure of simple phosphate glasses. Journal of
Non-Crystalline Solids , 263 , 1-28.
[5] Vogel, W. (1994) Glass Chemistry . 2nd edn. Heidelberg: Springer.