ZnO, SiO2, and SrO doping in resorbable tricalcium phosphates: Influence on strength degradation, mechanical properties, and in vitro bone-cell material interactions.

To understand the combined effects of ZnO, SiO(2), and SrO doping on mechanical and biological properties of tricalcium phosphate (TCP) ceramics, dense β-TCP compacts of different compositions (pure β-TCP; 1.0 wt % SrO; 0.25 wt % ZnO; 1.0 wt % SrO + 0.5 wt % SiO(2); and 1.0 wt % SrO + 0.25 wt % ZnO) were prepared via dry pressing followed by sintering at 1250°C. X-ray diffraction of sintered compacts revealed that dopants retarded β- to α-TCP phase transformation during sintering. Doping with SrO, SrO/SiO(2), and SrO/ZnO reduced compressive strength of the samples to 56% (173 ± 25 MPa), 57% (170 ± 15 MPa), and 47% (208 ± 72 MPa) of pure β-TCP (396 ± 58 MPa), respectively. However, addition of ZnO resulted in only 7% (365 ± 69 MPa) strength degradation. The impact of dopants on long-term in vitro strength degradation was evaluated by soaking in simulated body fluid (SBF) for a period of 8 weeks. In all cases, excellent apatite growth was observed on doped β-TCP samples. However, strength degradation rates were different depending on dopant chemistry and composition. Maximum degradation was observed in undoped and ZnO-doped β-TCP samples, which degraded to 41% and 68% of the original strength before soaking in SBF. Finally, in vitro cell-materials interaction study using human fetal osteoblast cells demonstrated that addition of dopants improved cell attachment and proliferation. These results indicate that tailorable strength and strength degradation behavior can be achieved in β-TCP via compositional modifications using small amount of dopants.