Abstract
Variations of surface structure and charge of sintered hydroxyapatite (HA) in SBF were investigated during forming bone like apatite using TEM-EDX and laser electrophoresis spectroscopy. TEM-EDX indicated that the HA increased its Ca/P rattio up to 1.84 during early soaking period in SBF to form a Ca-rich calcium phosphate, and then decreased the Ca/P ratio to 1.46 to form an amorphous calcium phosphate (ACP). Thereafter the ACP gradually increased its Ca/P ratio up to 1.65 to convert into crystalline apatite. Electrophoresis showed that surface charge of HA was highly negative immediately after soaking in SBF, increased up to positive value during subsequent period, and then again decreased to converge a constant negative value. Therefore formation of Ca-rich calcium phpsphate at an initial stage is attributed to combination of positively calcium ion in SBF on the negatively charged HA, and the subsequent formation of ACP with low Ca/P ratio is attributed to combination of negatively charged phosphate ion on the positively charged Ca-rich calcium phosphate. Since this phase is metastable, it eventually transformed into crystalline apatite.
