Synthesis of amorphous calcium phosphates for hard tissue repair using conventional melting technique

Abstract

The technical use of phosphate glasses has been restricted because of their strong hygroscopic nature. Traditionally phosphate glasses have been used as an opaline in silicate glasses since the solubility of phosphate in silicate glasses at lower temperature is very poor. Their poor chemical durability can be improved by the introduction of higher valency elements such as Ba, Al, or Be. The most important property of the phosphate glass is its ability to dissolve some elements and oxides that are insoluble or poorly soluble in glasses of other materials and crystalline compounds. Another important use of phosphate glasses is their application as biomaterials based on the calcium phosphate system. Their similarities in composition to bone and teeth make them ideal candidates. The first proposed application of the calcium phosphate glass to the biomaterials was proposed as dental restorative materials such as the crown because of their excellent castability as well as sufficient mechanical strength [1, 2]. The purpose of this study was to explore calcium phosphate glasses having an amorphous structure as potential biomaterials in hard tissue repair. We synthesized amorphous calcium phosphate glasses by melting and subsequent quenching process. Batches in the system CaO–CaF2–P2O5–MgO–ZnO were prepared with six kinds of Ca/P ratios from 0.2 to 1.2 using CaCO3, CaF2, H3PO4, MgO, and ZnO as raw materials. The molar ratio of CaO/CaF2 was fixed to 9. MgO and ZnO were added at 1 wt%, respectively. Mixed batches were dried at 80 ◦C and melted at temperatures ranging from 800 to 1550 ◦C depending on the Ca/P ratios. They were subsequently quenched onto the graphite plate at room temperature after melting. In order to determine the crystallinity and crystalline phases of the as-quenched samples, X-ray diffraction analysis was performed using Philips APD 3720 X-ray diffraction apparatus with a fine focus copper target X-ray tube. As shown in Fig. 1, there was no crystalline peak up to Ca/P of 0.6. When Ca/P ratio was 0.8, the sample exhibited the Zn3(PO4)2 as well as Ca2P2O7; the former had disappeared but the latter still remained. Ca2P2O7 phase partially transformed to Ca4P2O7 with increasing Ca/P to 1.2. Crystallinity Figure 1 XRD patterns of the as-quenched samples. • and denote Ca2P2O7 and Zn3(PO4)2, respectively.