Ceramics and composites - Orthopaedic Biomaterials in Research and Practice - page 207

The best known of these materials is Bioglass 45S5 (University of
Florida, Gainesville, Florida), developed by L.L. Hench and coworkers.
It contains SiO 2 , P 2 O 5 , CaO, and Na 2 O in a 45:6:24.5:24.5 weight per-
cent (w/o) ratio. This is a glass, with no crystalline phase, but it may be
combined with other less reactive materials to produce a glass phase-
containing ceramic. Bioglass has not yet been used as a load-bearing
material owing to its poor mechanical properties.
There are several known polycrystalline surface-active materials, the
best known being Ceravital (E. Leitz, Wetzlar, FRG). This material has
a similar composition to 45S5, but with more P 2 O 5 , less Na 2 O, and the
addition of K 2 O and MgO. Recent innovations have seen the develop-
ment of sol-gel processed glasses in the SiO 2 -CaO-P 2 O 5 system. These
bioactive gel-glasses are hydrolyzed at ambient temperatures and have
improved reactivity and degradability through an initial high specific
surface area. They are currently being investigated as coatings on alu-
mina implants. Osteoconductive properties of sol-gel processed glasses
are similar to melt-derived glasses. Within this group of materials, apa-
tite wollastenite glass ceramic (CaOSiO 2 ) is an alternative to Bioglass
with increased mechanical strength.

resorbable
ceramics

There has been a continual fascination with the concept of providing a
ceramic material for filling bony defects or augmenting bone healing
that would be gradually resorbed and replaced by tissue and that would
release only normal physiologic ions. Sterile plaster of Paris, sometimes
called surgical plaster ((CaSO 4 ) 2 *H 2 O), has been used in this application
since the 19th century, continuing up to today. It is usually preformed
into fully hydrated (“set”) pellets. However, it resorbs slowly and is rela-
tively weak. Thus, there has been a continual search for an alternative
material.
Most materials in development today are in the calcium-phosphorus
system, with Ca/P ratios varying from 1 (brushite) to 1.5 (tricalcium
phosphate), although others incorporate alumina and other nonresorb-
able or partially resorbable phases. The most exciting aspect of calcium
phosphate-based materials is their excellent biocompatibility and com-
positional similarities to natural bone. Doping these ceramics with vari-
ous metal ions has significantly influenced their properties. Resorbable
bioactive silica-calcium phosphate nanocomposite (SCPC75) has been
investigated as a novel controlled release carrier of antibiotics for the
treatment of osteomyelitis. It is believed to be viable for eradicating infec-
tion and stimulating bone cell differentiation and new bone formation.

Composite materials

A composite (material) is a material in which two or more different
phases are deliberately combined to obtain a material whose properties
are a mixture or composite of those of the individual materials. Thus,
carbon fibers may be placed in an epoxy matrix in an effort to obtain
a material with strength and stiffness (from the fibers) combined with