Physicochemical properties of TTCP/DCPA system cement formed in physiological saline solution and its cytotoxicity

In this paper, the physicochemical properties and cytotoxicity of calcium phosphate cement (CPC), prepared by mixing cement powders of tetracalcium phosphate (TTCP) and dicalcium phosphate (DCPA) with a cement liquid of physiological saline solution, were investigated. The microstructure evolution of various hardened cement bodies and their hydration crystals as a function of immersion time in similar physiological fluids, physiological saline solution (0.9% NaCl), or simulated body fluids (SBF), were also studied. Results show that the setting time of CPC is in the range of 12-15 min, which meets the clinical application demands. We also found that the mean compressive strength of the CPC samples immersed in SBF for 3 days is 104+/-10 MPa which reaches the transverse compressive strength, 106-133 MPa, of human long bone. The results obtained from both the X-ray powder diffraction analyses (XRD) and scanning electron microscopy (SEM) observations indicated that a reinforcing effect of some remaining TTCP particles in the early stages of immersion is mainly responsible for the increase in the initial strength. Although the CPC failed to keep this high level when immersed for a longer time, the initial reinforcing effect of the remaining TTCP particles provides advantages for clinical applications. This would be effective when the material is loaded at the very beginning of the implantation, especially for the material used as a fixation, which requires a certain initial strength in the early stages of the implantation. The cytotoxicity results showed that the relative growth rate (RGR%) of L929 cells on the CPC samples using physiological saline solution as a cement liquid was slightly superior to that of the samples using the 0.5 mol/L phosphate acid solution as the cement liquid. This was most likely caused by the pH difference between the two CPC samples immersed in a DMEM-BFS medium.