Si complexes in calcium phosphate biomaterials

Silicon complexes in silicon doped calcium phosphate bioceramics have been studied using Si-29 magic angle spinning nuclear magnetic resonance spectroscopy with the objective of identifying the charge compensation mechanisms of silicon dopants. Three different materials have been studied: a multiphase material composed predominantly of a silicon stabilized alpha-tricalcium phosphate (alpha-TCP) phase plus a hydroxyapatite (HA) phase, a single phase Si-HA material and a single phase silicon stabilized alpha-TCP material. NMR results showed that in all three materials the silicon dopants formed Q(1) structures in which two silicate tetrahedra share an oxygen, creating an oxygen vacancy which compensated the substitution of two silicon for phosphorus. This finding may explain the phase evolution previously found where silicon stabilized alpha-TCP is found at low temperature after sintering.