Crystallization and microstructure analysis of calcium phosphate-based glass ceramics for biomedical applications

Calcium phosphate glasses and glass ceramics (CaO/P2O5=1.25 in molar ratio) modified by small amounts of additives such as Na2O, MgO, TiO2 and ZrO2 were prepared after appropriate heat treatment for nucleation and crystallization. Based upon differential thermal analysis (DTA) results, a two-step heat treatment was used for crystal nucleation and growth. X-ray diffraction (XRD) analysis demonstrated that bioresorbable β-Ca2P2O7 (β-DCP), β-Na2CaP2O7, Na2Mg(PO3)4 phases were formed in the glass matrix depending upon the relative contents of the additives. By adding higher contents of Na2O and TiO2 and using CaO/P2O5=1.5–2.0, crystallization of β-DCP and Ca3(PO4)2 (β-TCP), and the formation of a dense structure in the glass ceramics were obtained. The precipitation of these crystals could be well distinguished at a magnification of 4000× and phases were dispersed in areas of micron size. A porous structure may be easily formed after the soluble phases are dissolved in physiological media. These glass ceramics with high CaO/P2O5 ratio, modified by the above mentioned additives are expected to find use as implants for bone replacement/regeneration and drug delivery carriers synergistically, because the soluble phases may act as drug delivery carriers and the porous structure will allow for bone ingrowth.