Biomedical Engineering Reference
In-Depth Information
FIGURE 5.7
If there is an insufficient amount of the patient's own bone or donor bone available to fill a
bone defect, synthetic bone graft substitutes made of calcium phosphate or calcium sulfate may be used. (a) These
are biphasic calcium phosphate granules made of hydroxyapatite and tri-calcium phosphate with an optimized
porosity and particle shape used for repair of mandibular bone defects (Straumann
W
BoneCeramic, Institut Strau-
mann AG). (b) The high porosity visible in this scanning electron micrograph allows maximum space for new
blood vessel ingrowth and bone cell influx.
or brushite, beta-tricalcium phosphate or tetracalcium phosphate, and amorphous calcium
phosphate. The stability of a given calcium phosphate medical device depends on the crystal
phase, the crystal size and perfection, the temperature used during processing, the density,
and the in-use environment. At physiological temperature and pH, hydroxyapatite is the
stable phase, and it generally takes a long time to resorb via physiochemical dissolution.
However, bone cells and other cells called macrophages can initiate cell-mediated resorption
of calcium phosphates by changing the local pH to acidic. Nonhydroxyapatite phases of
calcium phosphate or other calcium-based biomaterials such as calcium carbonate or calcium
sulfate can simply dissolve in the body and do not require cell-mediated resorption.
