Resorption rate tunable bioceramic: Si,Zn-modified tricalcium phosphate
An ideal bone implant material would support the activity of osteoblasts in the development of new bone, while simultaneously being resorbed by osteoblasts as part of the lifelong orderly process of bone remodeling. Silicon and Zinc modified tricalcium phosphate (Si,Zn-TCP), a biphasic material, was synthesized as a candidate for resorbable temporal bone implant having a controlled solubility and pharmaceutical effect to promote bone formation. From XRD and ICP analyses, it was shown that up to 10% Si and Zn were incorporated in tricalcium phosphate (TCP) without formation of a secondary phase. Changes in lattice parameters and unit volume of TCP as calculated by Rietveld analysis indicate that Si and Zn substitute for P and Ca respectively. Analysis of neutron powder diffraction data confirmed that 10% Si and Zn doped TCP has a rhombohedral structure (space group R3c, Z = 21), with the unit cell parameters a = b = 10.3958(1) A, c = 37.3122(7) A, alpha = beta = 90°, and gamma = 120° in the hexagonal setting. Of the five cation sites, Ca(5) and Ca(4) sites was substituted by Zn. According to the occupancy, multiplicity and total cation sites, the Zn substitution content is calculated to be 10.01% of total Ca sites. A fraction of Si substitutes for P(1) sites and the substitution content is calculated to be 3.86% of total phosphor sites. Si and Zn effect on dissolution behavior of TCP has been investigated. The dissolution study was carried out in the simulated body fluid (SBF) at 37°C. The experimental results show that the dissolution rate decreased with increasing Si and Zn content in TCP. Zinc inhibits HAp precipitation from SBF, while Si induces HAp formation. The additives may modify the dissolution mechanism by adjusting the phase composition, decreasing the solubility and changing the surface properties. The cytotoxicity test shows that Si and Zn addition has no cytotoxic behavior on the cell within the additive level employed in this study.